Tunnel Technical Report

Circumferential Transportation Improvements

in the Urban Ring Corridor

Urban Ring Phase 2

TECHNICAL TUNNEL ALTERNATIVES SUMMARY REPORT

November 2008

U.S. Department of Transportation Federal Transit Administration

Chelsea

Everett

Somerville

Cambridge

Brookline

Boston

Medford

Urban Ring Phase 2 Hatch Mott MacDonald Tunnel Alternatives Earth Tech, Inc. Summary Report for RDEIR/DEIS

Executive Summary

This document provides a summary of the tunnel alternatives developed as part of the combined Revised Draft Environmental Impact Report (RDEIR) and Draft Environmental Impact Statement (DEIS) process for the Urban Ring Phase 2.

The physical context and key constraints that influence the planning of a tunnel alignment within the project corridor are presented, including: geology; water courses; utilities; historic structures; and land use. A range of alignment alternatives have been developed including short tunnel and long tunnel options. The tunnel alignments have been further refined and developed on the basis of preliminary ridership and cost-benefit analyses, and in coordination with public consultation. The full range of alignment alternatives presented in this document are considered to be feasible from an engineering perspective, although costs, benefits, and impacts vary widely among the alternatives.

The principal tunnel elements comprise the portals, the running tunnels, and the stations. Typical cross sections have been developed based on the criteria presented in this document. The cross sections take into account potential Urban Ring Phase 3 rail transit requirements. It was shown that the current Phase 2 BRT requirements were the controlling factor in determining the cross section, and therefore there is no cost premium associated with the basic Phase 2 tunnel cross section. Further refinement to the BRT vehicle envelope in subsequent engineering studies may afford a reduction in the tunnel cross sectional area, and therefore cost.

There are a number of different tunneling techniques that can be used to construct the running tunnels. The primary ones to be considered are: cut and cover tunnel; sequential excavation method (SEM) mined tunnel; and tunnel boring machine (TBM) bored tunnel. Each of these techniques offers the possibility to construct a single tunnel carrying two lanes or two tunnels each carrying one lane. While each of these techniques has been considered, either exclusively or in combinations, in the development of the tunneled alignment alternatives, the initial assumption is that the running tunnels would be constructed using a TBM in a single bore configuration. It is considered that, at this stage in the planning process, this has not precluded the development of a viable alignment option, and that alternative construction methods and configurations (e.g. twin bored tunnels, cut and cover tunnels, or SEM mined tunnels) would be re-assessed during subsequent engineering studies and as more information on geology, hydrogeology, settlement and building response, electromagnetic field impacts, and noise and vibration becomes available. Similar to the running tunnels, there are a variety of construction techniques that can be used to build the underground stations. The use of an over-size TBM is not considered practicable at this stage, principally due to physical constraints of major segments of the corridor. SEM mined platform tunnels have been considered where required by site constraints, but for overall planning purposes, the conceptual design of a typical underground station is a cut and cover construction.

Compatibility of the alternative alignment options with Phase 3 rail alignments has been presented and all alignments will allow at least some portion of the Phase 2 BRT tunnel to be converted to Phase 3 rail use.

The alignment alternative development stages are presented and discussed, culminating in the recommendation of a Locally Preferred Alternative (LPA) for the busway tunnel. Recommendations for further work relating to the busway tunnel are also presented.

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List of Contents Page

Abbreviations iv

Glossary v

Chapters and Appendices

1 Introduction 1-1 1.1 Project Background 1-1 1.2 Need for Urban Ring Phase 2 Tunnel Analysis 1-2

2 Physical Context and Constraints 2-1 2.1 Location 2-1 2.2 Geology 2-3 2.3 Charles River 2-4 2.4 Muddy River 2-4 2.5 Stony Brook Culvert 2-4 2.6 Utilities 2-5 2.7 Historic Structures 2-7 2.8 Land Use 2-8

2.8.1 Parcel 18 West Property 2-8 2.8.2 Air Rights Parcel 7 Development 2-9 2.8.3 Longwood Medical and Academic Area 2-10 2.8.4 Boston University 2-10 2.8.5 Children’s Hospital Boston 2-11 2.8.6 Green Line “D” Branch and CSX Right-of-way Proposals 2-12

3 Tunnel Specifications and Characteristics 3-1 3.1 Tunnel Design Criteria 3-1

3.1.1 Spatial Requirements 3-1 3.1.2 Alignment 3-5 3.1.3 Underground Stations 3-6 3.1.4 Tunnel Systems and Operation 3-7 3.1.5 Fire Life Safety 3-11 3.1.6 Security 3-12

3.2 Construction Methodology 3-14 3.2.1 Cut and Cover Tunnel 3-14 3.2.2 SEM Mined Tunnel 3-16 3.2.3 TBM Bored Tunnel 3-18 3.2.4 Initial Recommendations 3-20

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3.3 Typical Tunnel Cross Sections 3-23 3.3.1 Tunnel Portals 3-23 3.3.2 Running Tunnels 3-25 3.3.3 Underground Stations 3-31

4 Alternatives Considered 4-1 4.1 Tunneled Alignment Alternatives – Development Stage 1 4-2

4.1.1 Alternative 3 4-3 4.1.2 Alternative 3A 4-8 4.1.3 Alternative 3B 4-8 4.1.4 Alternative 3C 4-10 4.1.5 Alternative 4 4-11 4.1.6 Alternative 4A 4-13

4.2 Tunneled Alignment Alternatives – Development Stage 2 4-15 4.2.1 Alternative 3A-1 4-15 4.2.2 Alternative 3A-2 4-16 4.2.3 Alternative 3A-3 4-16

4.3 Tunneled Alignment Alternatives – Development Stage 3 4-17 4.3.1 Alternative H2(T) – “Tight Turn” 4-17 4.3.2 Alternative H2(T) – “Wide Turn” 4-18 4.3.3 Alternative H2(T) – Sub-options 4-19

4.4 Tunneled Alignment Alternatives – Summary 4-23 4.4.1 Noise and Vibration 4-23 4.4.2 Electromagnetic Fields 4-24 4.4.3 Phase 3 Compatibility 4-25 4.4.4 Preliminary Capital Cost Estimate of Options 4-27

5 Current Locally Preferred Alternative for Busway Tunnel 5-1

6 Conclusions and Recommendations for Further Work 6-1

Attachment A Typical Station Layout A-1

Attachment B Tunneled Alignment Alternatives B-1 B.1 Alternatives Development Stage 1 B-2 B.2 Alternatives Development Stage 2 B-3 B.3 Alternatives Development Stage 3 B-4

Attachment C Alternative H2(T) Sub-options Memorandum C-1

Attachment D Current LPA Busway Tunnel D-1 D.1 Preliminary Plan and Profile Drawings D-2 D.2 Estimate of Truck and Rail Car Numbers During Construction D-3

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Figures and Tables

Figure 2.1: Study Corridor ......................................................................................................................... 2-2 Figure 2.2: Stony Brook Culvert ................................................................................................................ 2-5 Figure 2.3: MWRA Pumping Station Shaft ............................................................................................... 2-6 Figure 2.4: 440 Park Drive ......................................................................................................................... 2-7 Figure 2.5: Northeastern University Parcel 18 West Development ........................................................... 2-8 Figure 2.6: Air Rights Parcel 7 Development ............................................................................................ 2-9 Figure 2.7: Children’s Hospital Boston 819 Beacon Street Development ............................................... 2-11 Figure 2.8: Green Line Storage Track Adjacent to Fenway Station (looking northeast) ......................... 2-12 Figure 2.9: Mixed Use Path Proposals ..................................................................................................... 2-13 Figure 3.1: BRT Clearance Envelope (Two-way busway tunnel).............................................................. 3-2 Figure 3.2: BRT Clearance Envelope (One-way busway tunnel) .............................................................. 3-3 Figure 3.3: Phase 3 Clearance Envelope (rail) ........................................................................................... 3-4 Figure 3.4: Typical Slurry Wall Equipment for Cut and Cover Construction.......................................... 3-15 Figure 3.5: SEM Mined Tunnels Using Multiple Drifts .......................................................................... 3-16 Figure 3.6: SMART Project Tunnel Boring Machine (43’-4” diameter) ................................................. 3-19 Figure 3.7: Typical Cross Section – Tunnel Portal Approach Ramp ....................................................... 3-24 Figure 3.8: Typical Cross Section – Cut and Cover Section .................................................................... 3-24 Figure 3.9: Typical Cross Section – Twin Bored Tunnels ....................................................................... 3-25 Figure 3.10: Typical Cross Section – Single Bored Tunnel ..................................................................... 3-28 Figure 3.11: Examples of Constrained Tunneling Worksites................................................................... 3-30 Figure 4.12: Leon Street Portal Worksites ................................................................................................. 4-4 Figure 4.13: Longwood Avenue (Avenue Louis Pasteur) Station Worksites ............................................ 4-5 Figure 4.14: Abandoned Rail Freight Spur / Landmark Center Portal..................................................... 4-10 Figure 4.15: Underground Stations on the Green Line ............................................................................ 4-21 Figure 4.16: Longwood Avenue Alignment............................................................................................. 4-22 Figure 5.1: LPA Busway Tunnel................................................................................................................ 5-2 Table 3.1: Summary of Alignment Criteria................................................................................................ 3-5 Table 3.2: Platform Lengths ....................................................................................................................... 3-6 Table 4.3: Phase 3 Compatibility Matrix ................................................................................................. 4-26 Table 4.4: Preliminary Estimate of Capital Cost for Tunnel Alternatives ............................................... 4-27 Table 5.1: Summary of LPA Tunnel Lengths ............................................................................................ 5-1

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Abbreviations BRT Bus Rapid Transit

BU Boston University

CAC Citizens Advisory Committee

CNG Compressed Natural Gas

DEIS Draft Environmental Impact Statement

ECD Emission Controlled Diesel

EMF Electromagnetic Field

EMI Electromagnetic Interference

GJRR Grand Junction Railroad

LMA Longwood Medical and Academic Area

MBTA Massachusetts Bay Transportation Authority

MIS Major Investment Study

MTA Massachusetts Turnpike Authority

MWRA Massachusetts Water Resources Authority

NAVD North American Vertical Datum

NFPA National Fire Protection Association

NGVD National Geodetic Vertical Datum

RDEIR Revised Draft Environmental Impact Statement

ROW right-of-way

SEM Sequential Excavation Method

TBM Tunnel Boring Machine

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Glossary

Busway – dedicated right-of-way provided for exclusive use of the Bus Rapid Transit service.

Cut and cover tunnel – a method of tunnel construction involving the installation of earth support systems (e.g. slurry walls) followed by the main excavation, placing of the base slab, roof slab and subsequent backfilling to the final ground level.

Sequential Excavation Method – a method of tunnel construction that involves the use of standard construction equipment for excavation. The tunnel is usually lined in two steps: An initial lining of sprayed concrete provides immediate support and a subsequent secondary or permanent lining is then placed using either sprayed concrete or cast insitu concrete. A waterproof membrane is usually installed between the primary and secondary linings.

Slurry wall – a form of earth support system whereby a continuous trench is excavated in the ground to the required depth, using slurry to provide temporary support during excavation of the trench. Reinforcement (which may be reinforcing cages or steel H sections) is lowered into the trench and concrete is subsequently placed by tremie pipe, displacing the slurry from the trench.

Tunnel Boring Machine – a method of tunnel construction that involves the procurement of a custom-made piece of construction equipment. The TBM is equipped with a cutterhead that is used to mine the ground. The excavation is continuously supported by installing precast concrete segments within the TBM and grouting them in place as the machine advances.

Tunnel eye – the interface point of cut and cover tunnel and the bored or mined tunnel.

Tunnel portal – the interface point of the open cut and the cut and cover tunnel.

Tunnel portal approach ramp – open retained cut that takes the alignment from ground level down to the tunnel portal.

Tunnel portal structure – all structural elements associated with the transition from a grade level alignment to a bored or mined tunnel alignment.


1 Introduction

This document provides a summary of the tunnel alternatives developed as part of the combined Revised Draft Environmental Impact Report (RDEIR) and Draft Environmental Impact Statement (DEIS) process for the Urban Ring Phase 2. The document presents the key design criteria used in developing the tunnel alternatives, provide a brief narrative of the alternatives developed, and outlines some of the main issues in relation to constructability, operation, and potential conversion to Phase 3 (rail). It is intended that the text from this report will be used in preparing the RDEIR/DEIS, and therefore the project introduction will be kept very brief in this report, as it is anticipated to be covered by others in the environmental document.

1.1 Project Background

The idea of transportation improvements in the Urban Ring Corridor has been the subject of considerable public debate and analysis dating back to the era when a system of circumferential highways were proposed and later abandoned. The 1970’s marked a period of fundamental change in state policy away from highways and in favor of transit based solutions to mobility problems. Starting with the Circumferential Transit Feasibility Study in 1989, potential ridership in the Corridor began to be quantified and the cost and feasibility of various alternatives was examined in greater detail. The Urban Ring Major Investment Study (MIS) completed in 2001 presented the approach of three additive phases to transit improvements in the Corridor:

Phase 1 New and improved cross-town bus routes on existing streets;

Phase 2 Addition of Bus Rapid Transit (BRT) routes with new and improved inter-modal connections; and

Phase 3 Addition of rail rapid transit.

The MIS evaluated various tunneled alternatives for Phase 3 rail transit. As part of the Phase 2 RDEIR/DEIS process the possibility of providing a portion of the Phase 3 tunnel alignment earlier in the project, during Phase 2, is to be investigated. Under this scenario, the tunnel alignment would be used by the BRT service during Phase 2, and subsequently converted to rail usage in Phase 3. This report presents the tunnel alignment alternatives developed for operation with BRT in Phase 2, and also addresses issues related to the potential conversion of the tunnel from Phase 2 BRT to Phase 3 rail transit.

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1.2 Need for Urban Ring Phase 2 Tunnel Analysis

The Urban Ring Phase 2 is the subject of the current planning and environmental review process. The proposed Urban Ring Phase 2 project would be bus rapid transit (BRT), a form of transit that uses rubber-tired bus vehicles with a comprehensive system of improvements that are designed to enable service quality that is more like that of rapid transit. These improvements include provision of dedicated right-of-way (i.e. special bus roadways referred to as “busways,” or bus lanes on general traffic roadways); widely-spaced stops with substantial transit stations that have a distinct transit identity; high-capacity vehicles with low floors and low emissions; high-frequency service; and advanced communications and traffic control technologies.

The provision of dedicated right-of-way (ROW), in the form of busways and bus lanes, is central to effective and efficient operation of the Urban Ring Phase 2. Wherever possible, surface busways or bus lanes have been proposed for the Urban Ring Phase 2 BRT service. In areas where busways or bus lanes are not feasible, the Urban Ring Phase 2 BRT service may need to operate in mixed traffic.

There are, however, some areas in the Urban Ring Phase 2 corridor where significant segments of dedicated ROW are not available and heavy traffic congestion limits the speeds that are possible for BRT vehicles operating in mixed traffic. In order to address these challenges, the Urban Ring Phase 2 project team investigated the potential travel time improvements, ridership benefits, construction impacts, and cost implications of tunnels in certain segments of the Urban Ring Phase 2 corridor.

This technical memorandum summarizes the analysis of potential tunnel alternatives and options for the Urban Ring Phase 2, including the issues and constraints, design criteria and specifications, potential tunnel alignments, and key findings of the analysis. The tunnel analysis encompasses a range of different tunnel lengths and connections, but all of the tunnel alternatives include a segment beneath the Longwood Medical and Academic Area (LMA). The LMA has a very high density of travel demand, making it an important hub for Urban Ring Phase 2 service, but also very high levels of traffic congestion and limited opportunities for dedicated ROW at the surface.


2 Physical Context and Constraints

2.1 Location

The Urban Ring Phase 2 RDEIR/DEIS Study Corridor is shown in Figure 2.1. The MIS identified two Phase 3 tunnel alignments that connect the Orange Line at Assembly Square with the former Orange Line terminus at Dudley Square. At a general level, points north and south of the Charles River and west into Allston formed the broad limits of the tunnel alternatives considered, all of which included a tunnel and one or more underground stations in the Fenway/Longwood Medical and Academic Area (LMA). The general extent of the corridor for which tunnel alternatives have been assessed as part of the Urban Ring Phase 2 RDEIR/DEIS process, is shown in Figure 2.1.

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Urban Ring Phase 2 Corridor

Section of Corridor Assessed for Tunneled

Alignments

Figure 2.1: Study Corridor

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2.2 Geology

At present there is a lack of site-specific geological or geotechnical information along the potential Urban Ring tunnel alignments. Presented below is a general summary of the regional geology interpreted from secondary sources. Geotechnical investigations should be performed during subsequent planning phases of the project to better determine the geotechnical characteristics along the proposed tunnel alignments.

In general, the area through which the Urban Ring tunnels would be constructed is the site of an ancient estuary. As a result, the area is typically characterized by marine and glacial deposits and extensive layers of organic silts and clays. Upland areas are generally overlain by glacial till (a typically hard and compact mixture of clay, silt, sand, pebbles, cobbles and boulders); and lowland areas typically have stratified deposits near the surface, which may include both sands and gravels, and fine-grained silts and clays. In the lowest lying areas, near the Charles River and the Muddy River, an extensive, fine-grained deposit known as the Boston blue clay was deposited under shallow marine conditions. This is overlain by recent estuarine deposits, which in turn are overlain by artificial fill in some areas.

At the northern end of the tunnel alignments in the vicinity of Boston University (BU) Bridge and Commonwealth Avenue, the soil conditions are variable, but typically include fills, organic silts, sand/gravels and clay. Along the shores of the Charles River and along Commonwealth Avenue, depths of up to 15 feet of miscellaneous fill was found to overlie pockets of organic silts. The organic silts are typically thicker towards the river. Beneath the organics is a deep deposit of granular soil, a stratum that ranges from fine to coarse sands with occasional pockets of clay within the stratum. The top of the Boston Blue Clay formation in this area was found to be greater than 100 feet below ground surface.

At the west end of Ruggles Street, the upper soils include about 10 feet of fill underlain by up to 20 feet of organic silts underlain by a thin layer of sand and then Boston Blue Clay. However, as the profile moves easterly, the organics taper out and the fill is underlain by sand and sand with gravels which in turn is underlain by clay. The clay deposit is quite thick in the Ruggles Street area, extending to depths in excess of 150 feet.

The bedrock of the lower Charles River watershed comprises a sequence of sedimentary and volcanic rocks that were deposited about 600 million years ago. The rock layers vary from relatively soft siltstones and slates (known as Cambridge Argillite), to harder conglomerates consisting of pebbles and cobbles in a sand matrix (for example the Roxbury Conglomerate). Uplands in Newton, Brookline, and the southern portion of Boston are underlain by the hard conglomerate and volcanic rocks; lowlands in Cambridge and the northern portion of Boston are underlain by the argillite.

The bedrock elevations in the project area vary and are expected to have a high point in the vicinity of Harvard Medical School on Longwood Avenue at around 70 to 95-ft below ground level.

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2.3 Charles River

Water depths in the Lower Charles River range from 6-ft to 12-ft in the basin upstream of the Boston University Bridge and 9-ft to 36-ft in the lower basin1.

2.4 Muddy River

Preliminary information received from the United States Army Corps of Engineers for the Muddy River Flood Damage Reduction and Environmental Restoration Project (Phase I) indicates that the Muddy River will be day-lighted through the Sears Rotary area to an invert elevation of approximately -4.0-ft to -5.0-ft based on North American Vertical Datum 1988 (NAVD 88). NAVD 88 is 0.65-ft below National Geodetic Vertical Datum 1929 (NGVD 29).

As part of the Muddy River project two new pile-supported bridge structures will be built, one under the Riverway (at the western end of the Sears Rotary) and one under Brookline Avenue (at the eastern end of the Sears Rotary). The current design for the Muddy River restoration project will eliminate the jughandle turn east of Brookline Avenue, so this road will not require a bridge structure. The toe elevations of the drilled shaft foundations for the new bridge structures range from -38.5 to -57.5-ft, NAVD 88. Any Urban Ring Phase 2 tunnel alternatives passing beneath these planned bridge structures would need to either provide sufficient ground cover beneath the drilled shaft foundations, or underpin and support the bridge structures during construction of the Urban Ring tunnels.

2.5 Stony Brook Culvert

The Stony Brook tributary of the Lower Charles River was culverted in the late 19th and early 20th centuries. The culvert runs north-south along Parker Street and crosses perpendicular to Ruggles Street, as shown in Figure 2.2. The combined width of the twin culvert structure is approximately 32-ft and the crown of the culvert is located immediately below street level. Where the culvert crosses Ruggles Street it does not appear to be supported on piled foundations and the bottom of the construction is approximately 17-ft below ground level.

As a result of these conditions, an Urban Ring Phase 2 tunnel that follows the alignment of Ruggles Street would need to pass beneath the Stony Brook Culvert. This would require either an increase in the tunnel depth at this point to provide sufficient ground cover below the culvert, or underpinning and support of the Stony Brook Culvert during construction.

1 According to the draft publication for the USEPA “A Hydrodynamic and Water Quality Model for the Lower Charles River Basin, Massachusetts”, dated November 2005.


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Source: MASCO

Figure 2.2: Stony Brook Culvert

2.6 Utilities

Utility diversions are costly and disruptive in their own right and therefore any alternative should seek to

minimize the impact on existing utilities where possible. At this stage in the project there is little

information on existing utilities along the Urban Ring corridor. As more utility information has become

available during the development of the alignment alternatives it has been included in the consideration of

alignment alternatives.

The Stony Brook Culvert, as discussed above, is located beneath Parker Street. Located to the east of

Huntington Avenue and in the grounds of the Wentworth Institute of Technology, the Massachusetts

Water Resources Authority (MWRA) operates a pumping station (see Figure 2.3) that connects four major

sewer lines:

• South Charles Relief Sewer (108” internal diameter) that crosses under Huntington Avenue;

• Boston Main Drainage Relief Sewer (78” internal diameter) that runs under Ruggles and

Huntington Avenue;


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• Charles River Valley Sewer (78” × 84”) that crosses under Huntington Avenue from Vancouver Street; and

• Mission Hill Relief Sewer (78” × 84”) under Vancouver Street.

Urban Ring Phase 2 tunnel construction would seek to avoid or minimize impacts to utilities wherever practicable, particularly to strategic infrastructure such as the MWRA pump station and these four sewer lines.

The type and extent of mitigation required for utilities will depend on the utility and the owner or agency requirements, the age of the structure, the sensitivity to ground movements, the risks associated with potential damage, the method of construction proposed for the Urban Ring, the proximity of the proposed Urban Ring infrastructure to the utility, and safety and security considerations with respect to existing and proposed infrastructure.

Source: MASCO

Figure 2.3: MWRA Pumping Station Shaft

MWRA Shaft Huntington Avenue Ruggles Street


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2.7 Historic Structures

Listed structures have been investigated during later stages of option development. One particular structure of note is the building at 440 Park Drive, currently used by the Boston Youth Fund, owing to the possible location of a tunnel portal in this area. The building at 440 Park Drive is identified as the Riverway Administration Building (BOS.7536) in the MACRIS database. The building was designed by Shepley, Rutan and Coolidge and construct circa 1898. The building is within the Back Bay Fens section of Olmstead Park System (BOSIO) and Emerald Necklace Parks (BOSJE) National Register Historic Districts (listed December 8, 1971) and furthermore is listed as a local landmark (December 18, 1989). On June 5, 1998 a preservation restriction was enacted for the Emerald Necklace Parks. The building facilities also include a yard and a refueling station, as shown in Figure 2.4.

Figure 2.4: 440 Park Drive

Park Drive

Refueling Station

Emerald Necklace


2.8 Land Use

There are a number of ongoing and incipient development projects on or near the proposed Urban Ring Phase 2 project alignment. The Urban Ring Phase 2 project team have coordinated with appropriate institutions and developers to ensure consistency between the land use proposals and the Urban Ring Phase 2 recommendations.

Some key land parcels along the Urban Ring corridor that are either under development, have development proposals, or have some other significant are highlighted below.

2.8.1 Parcel 18 West Property

Northeastern University is currently developing the Parcel 18 West property into the Parcel 18 West Development, an approximately 1,200-bed, 22-story student residence building and a six-story mixed-use building. Parcel 18 West was previously occupied with a 162-space surface parking lot, and is located at the intersection of Tremont Street and Ruggles Street (see Figure 2.5).

Source: Institutional Master Plan Notification Form, Northeastern University, July 10, 2006

Figure 2.5: Northeastern University Parcel 18 West Development

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2.8.2 Air Rights Parcel 7 Development

Meredith Management’s proposed development is sited on the Massachusetts Turnpike Authority’s Parcel 7 land and air rights, bounded by Beacon and Maitland Streets to the west, and Brookline Avenue to the east. The Parcel is within a block of Fenway Park, the Lansdowne Entertainment District and Kenmore Square. The Beacon Street level plan for the development of Air Rights Parcel 7 is shown in Figure 2.6.

Source: Project Notification Form, Massachusetts Turnpike Parcel 7 Air Rights, Kenmore/Fenway Area, January 16, 2008

Figure 2.6: Air Rights Parcel 7 Development

Beacon Street Brookline Ave


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2.8.3 Longwood Medical and Academic Area

The Longwood Medical and Academic Area (LMA) is an important regional employment center along the Urban Ring corridor with various medical, academic and research institutions, comprising many distinct facilities. Most of these institutions have active, pending, or proposed construction projects that will affect both travel demand and physical constraints for Urban Ring Phase 2 surface and tunnel options. Each of these institutions has a master plan describing its future development proposals. The Urban Ring Phase 2 project team has reviewed these master plans and met with LMA institutions to better understand future demands and constraints. The tunnel alternatives reflect the project team’s best understanding of development proposals in the LMA.

2.8.4 Boston University

Boston University has developed a long-term vision for the land around the south end of Boston University Bridge. This vision includes MTA air rights parcels, reconfiguration of Mountfort Street, and a potential new transportation hub. BU’s 2007 Strategic Plan1 discusses some of these proposals:

“Our current master planning, which looks out over the next quarter-century, calls for the creation of a major regional transportation hub roughly at our end of the BU Bridge, including the rationalization of the various roads, light rails, and railroads that traverse this very busy intersection. It also calls for a reinforcement of the “short axis” of our campus, with the thoughtful use of air rights over the Mass Pike giving us more room for concentrated growth and—just as important—physical cohesion.”

1 “Choosing to be Great, A Vision of Boston University – Past, Present, and Future – The University’s 2007 Strategic Plan”, Draft, dated October 19th 2007. Source: http://www.bu.edu/strategicreport/


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2.8.5 Children’s Hospital Boston

Children’s Hospital Boston are planning to develop the parcel at 819 Beacon Street to include a residential

building fronting onto Beacon Street with a multi-story parking garage to the rear. The project is located

on the south side of Beacon Street between Munson Street and Maitland Street and will be located

adjacent to the proposed Parcel 7 Air Rights development. The lobby level plan for the development is

shown in Figure 2.7.

Source: Children’s Hospital Boston, 819 Beacon Street Project (Lobby Level), Elkus Manfredi Architects, August 3, 2006

Figure 2.7: Children’s Hospital Boston 819 Beacon Street Development


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2.8.6 Green Line “D” Branch and CSX Right-of-way Proposals

During the development of the RDEIR/DEIS alignment alternatives the MBTA constructed a storage track for the Green Line “D” Branch to the east of Fenway station and beneath Park Drive within the CSX right-of-way, as shown in Figure 2.8.

Figure 2.8: Green Line Storage Track Adjacent to Fenway Station (looking northeast)

There are proposals for a pedestrian and bicycle path utilizing the abandoned rail freight spur adjacent to the Green Line “D” Branch between Park Drive and Miner Street, sharing the strip of land that now contains the Green Line storage track. Draft proposals to accommodate both the storage track and the multi-use path are shown in Figure 2.9.

Fenway Station Storage track Park Drive

440 Park Drive CSX Right-of-way


Figure 2.9: Mixed Use Path Proposals

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3 Tunnel Specifications and Characteristics

To provide a framework for development of alignments and conceptual designs for the Urban Ring Phase 2 busway tunnel, it was necessary for the project team to set certain technical parameters and assumptions. These include a wide range of design criteria, including appropriate tunnel dimensions and other specifications. The project team also reviewed the available tunnel construction methods and evaluated them relative to the project’s needs and constraints.

In the course of developing technical parameters and tunnel alignment options for Urban Ring Phase 2, the project team has also given significant consideration to the potential for converting the tunnel for use in Urban Ring Phase 3, which would use either light rail or heavy rail as the mode of transport. In analyzing the various Urban Ring Phase 2 tunnel options, the project team has taken care to ensure that the Urban Ring Phase 2 proposals accomplish the following, where possible:

• Do not preclude the development of Urban Ring Phase 3 in any form that may reasonably be expected (e.g. light rail or heavy rail, in a range of potential alignments); and

• Where possible, include some minor alterations to Urban Ring Phase 2 that would facilitate the transition to Urban Ring Phase 3.

3.1 Tunnel Design Criteria

This section provides a summary of the design criteria used in the development of tunnel alternatives for Urban Ring Phase 2. These design criteria will help to inform choices and assumptions about tunnel geometry, design, alignment, and construction assumptions for the tunnel alternatives. The tunnel design criteria include the following:

• Spatial Requirements;

• Alignment;

• Underground Stations;

• Fire Life Safety; and

• Tunnel Systems and Operation.

3.1.1 Spatial Requirements

The vehicular clearance envelope required for a two lane bi-directional busway tunnel is shown in Figure 3.1. Within covered tunnel sections there is likely to be a central dividing wall required for ventilation purposes. A central median may also be required to ensure that a head-on collision between two buses traveling in opposite directions is avoided. If a central dividing wall is provided then each lane is treated as a separate single lane busway tunnel and the clearances shown in Figure 3.2 are adopted. The section shown in Figure 3.1 is used primarily in open cut approach ramps.

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The preferred lane width is 12.0-ft and the minimum vertical clearance is 14.5-ft minimum to any structure. The clear vertical distance to any tunnel services or signage suspended above the roadway is taken to be 15.0-ft, allowing an additional 0.5-ft vertical clearance. In addition to these dimensions walkways would be provided on each side of the roadway.

12'-0"

CL

6'-0"

1'-0"

14'-0"

15'-0"

STRUCTUREGAGE

ROADWAYSURFACE

14'-6

"

7'-6

"

NICHE(1'-0" DEEP)

MINIMUM WITH NICHE

MINIMUM WITHOUT NICHE

LANE CL LANE

Figure 3.1: BRT Clearance Envelope (Two-way busway tunnel)

The requirements for a single lane uni-directional busway tunnel are shown in Figure 3.2. A walkway would be provided on one side of the roadway.

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12'-0"

CL

6'-0"

1'-0"1'-0"

15'-0"

16'-0"

STRUCTUREGAGE

ROADWAY SURFACE

14'-6

"

7'-6

" NICHE(1'-0" DEEP)

MINIMUM WITH NICHE


LANE

Figure 3.2: BRT Clearance Envelope (One-way busway tunnel)

In all of the alternatives examined below, walkways are provided throughout the tunnel to allow for safe access during routine maintenance operations, without the need to close the tunnel. It is recommended that a minimum walkway width of 3.0-ft be provided for maintenance purposes. If it is not practicable to provide a 3.0-ft walkway, then it is recommended that a 2.0-ft walkway is provided with refuge niches, sized at 7.5-ft high by 2.0-ft wide and 1.0-ft deep, spaced at 20.0-ft centers. The refuge niches should be protected from errant vehicles.

Additional elements that need to be incorporated in the tunnel cross section but are not defined at this stage may include: signaling and signage; lighting; fire-life safety systems; and drainage. Some of these items can be incorporated within the required tunnel cross section. Other elements would require special design and construction accommodation.

Phase 3 would involve conversion of the BRT tunnels for use by either light rail or heavy rail. The clearance envelopes for Phase 3 have been based on those for the MBTA Green Line and Orange Line for light rail and heavy rail, respectively. The rail clearances are shown in Figure 3.3.

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3'-9"

CL

6'-6"

8'-0"

8'-6"

STRUCTUREGAGE

TOP OF RAIL

10'-3

"

7'-6

"

14'-6

" (G

RE

EN

LIN

E)

15'-0

" (O

RA

NG

E L

INE

)

NICHE(1'-0" DEEP)

PREFERRED


MINIMUM WITH NICHE

TRACK

Figure 3.3: Phase 3 Clearance Envelope (rail)

The development of tunnel cross sections that meet the busway spatial requirements provide sufficient space to accommodate either light rail or heavy rail transit clearance requirements, as shown in Figure 3.3. Therefore, designs that allow for the BRT clearance requirements above would also be consistent with any Urban Ring Phase 3 options. Further discussion on the typical tunnel cross sections that accommodate these spatial requirements is given in Section 3.3.

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3.1.2 Alignment

The design speed for BRT in tunnels is 30-mph, while the posted speed limit and assumed maximum operating speed would be 25-mph (to provide for a more conservative design for vehicle envelope). The 25-mph speed limit may be reduced at specific locations where warranted by special conditions, for example on approach to stations and at sharp turns.

The horizontal and vertical alignment criteria used to set out the alternative tunnel alignments are summarized in Table 3.1. The criteria are presented with respect to Phase 2 BRT and Phase 3 light rail/heavy rail. The tunnel alignments have been developed, as far as practicable, to be in conformance with the requirements of Phase 3. However there are certain locations where compliance with Phase 3 criteria has not been achieved for reasons relating to constructability, Phase 2 operability, or for other technical reasons. Where Phase 3 compatibility has not been achieved for a specific tunnel alignment, this fact has been noted, along with remedial actions that would need to be taken to enable Phase 3 implementation.

BRT Light Rail Heavy RailHorizontal Alignment

Minimum tangent lengthGeneral - 75 ft 75 ftBeyond station platform - - 65 ft

Minimum radiusGeneral 250 ft 250 ft 1800 ftApproaching station - - 700 ftAbsolute minimum 100 ft 150 ft 700 ftMinimum length of curve - - 75 ft

Reverse curvesMinimum tangent length between curves - 75 ft -

Vertical AlignmentGradients - general

Minimum grade - - -Preferred maximum grade 5.0% 5.0% 3.0%Absolute maximum grade 8.0% 7.0% 4.0%Preferred minimum length - 200 ft 200 ftAbsolute minimum length - 75 ft 75 ft

Gradients - stationsPreferred grade - - 0.0%Maximum grade - 1.0% 0.5%

Vertical curveMinimum length - crest L = 32.8 D * L = 0.034 DV2 L = 0.0344 DV2

Minimum length - sag L = 39.4 D * L = 0.034 DV2 2 × LAbsolute minimum length - 70 ft 100 ft

L = length of curve in feetD = algebraic difference in grade (%)V = train speed in miles per hour* Based on 30 mph design speed

Table 3.1: Summary of Alignment Criteria

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It is acknowledged that allowing for future conversion to heavy rail imposes certain restrictions on horizontal radii and on gradients. For current planning purposes, a minimum horizontal radius of 700-ft has been assumed to allow for Phase 3 rail conversion. Sharper radii (less than 700-ft) can be achieved, and some options that have been developed with tighter radii are only compatible with light rail vehicles as a result. However, in general, options are being developed to be heavy rail compatible to keep open all potential Phase 3 recommendations from the Major Investment Study (MIS).

3.1.3 Underground Stations

The controlling factors for the overall length of the station construction will be the platform length required, the vertical circulation elements (passenger access and egress), and the ventilation equipment to be located at each end of the station. An underground platform length of 220-ft has been assumed for Phase 2, which is comparable to the MBTA Silver Line platform length. The platform lengths for Phase 2 and Phase 3 underground stations are shown in Table 3.2. Additional factors affecting the final station dimensions will include the requirements for plant and equipment rooms, substations, communications equipment, machine rooms, fare collection facilities, vertical circulation elements, and site constraints.

Platform Length

Phase 2 – BRT 220-ft

Phase 3 – Light Rail 300-ft

Phase 3 – Heavy Rail 410-ft

Table 3.2: Platform Lengths

The project team has reviewed different options for accessing the underground station platforms, either from a central location along the platform (center-loaded) or from the end of the platform (end-loaded). In general, spatial constraints in relation to buildings, foundations, and other existing infrastructure would be a governing factor in the arrangement of access to the platforms.

Alternatives for station construction using cut and cover tunnel methods and sequential excavation methods (mined tunnels) have been investigated. The selected method would depend on a number of factors, including: the location of the station; the site constraints; and the geology and groundwater conditions. Construction methodology is discussed in more detail later in this report.

Depending on the alignment alternative developed, potential underground stations were investigated at the following locations:

• Ruggles Station;

• Huntington Ave (Green Line “E” Branch);

• Longwood Ave – at Avenue Louis Pasteur/Tugo Circle or at Brookline Avenue;

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• Yawkey Commuter Rail;

• Kenmore Square;

• Boston University Bridge (west, central, and east);

• Longwood (Green Line “D” Branch);

• Hawes Street (Green Line “C” Branch);

• Park Drive (Green Line “C” and “D” Branches); and

• West Station (Allston).

The following assumptions have been made in relation to platform layouts:

1. 12.0-ft nominal platform width;

2. 8.0-ft minimum platform width at objects/stairs/escalators etc.;

3. 10.0-ft vertical clearance above platform to any overhead signage, lighting etc.;

4. 0.75-ft platform height;

5. 4,000-ft minimum horizontal radius for convex platforms; and

6. 5,000-ft minimum horizontal radius for concave platforms.

The major items to be considered for conversion of the stations from Phase 2 to Phase 3 will be:

• Extension of the station and platforms;

• Installation of track;

• Installation of rail systems and signaling;

• Modifications to the tunnel ventilation and fire life safety systems;

• The elevation of the station platform; and

• The potential requirement for crossovers.

3.1.4 Tunnel Systems and Operation

There will be a number of systems required within the tunnel and associated structures to enable the safe operation of BRT services. The systems are discussed below.

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(i) Tunnel Ventilation

The general objective of a tunnel ventilation system is to ensure a safe and tenable environment under reasonably anticipated operating conditions for passengers and employees, covering normal, congested, and emergency scenarios.

The tunnel ventilation system will need to address the implications of vehicle engine choice for the BRT vehicles. The four main options considered are:

(a) Emission Controlled Diesel (ECD);

(b) Compressed Natural Gas (CNG);

(c) Dual Mode (electrified trolley bus in the tunnels); and

(d) Hybrid Electric (battery powered in the tunnels).

Ventilation of the tunnels may be broadly classified as natural, vehicle-induced, and mechanical. Natural ventilation relies on the pressure difference between the tunnel portals and shafts created by changes in elevation, air temperature, and wind. Vehicle-induced ventilation is due to the piston effect of vehicles moving through the tunnels.

For the case of BRT tunnels and stations the specific objectives of tunnel ventilation systems are to:

• Dilute vehicle exhaust emissions such as CO, NOx and particulate matter to acceptable levels during all operating conditions (ECD and CNG only).

• Remove heat generated by the vehicles (mainly radiators, engines and air conditioning units) and other heat sources within the tunnels and stations.

• Provide air exchange with the atmosphere.

• Control and purge smoke and hot gases generated during a tunnel or station fire.

It is assumed that both dual-mode and hybrid vehicles will be 100% electrically operated within the tunnel (the diesel engines will be completely shut-off), and as such underground emissions are not applicable to these choices of vehicle.

The emissions associated with CNG and ECD vehicles are not considered to be significantly different. This statement will require substantiation during design, but it is estimated that the particulate matter and CO2 released into the system will be similar for both vehicles, the NOx emissions will be less for CNG, but that the CO and toxic emissions will be significantly higher. For both these vehicle choices some ventilation is considered likely while the buses are idle in the stations. This may represent a separate discrete system, or could consist of the emergency tunnel ventilation fans operating at a lower capacity to induce draft through the facilities. Without further analysis it is not possible to determine whether the movement of the vehicles through the tunnels will be enough to generate sufficient air exchange to adequately dilute the vehicle exhaust and to provide air exchange for the passengers while the vehicles are passing through the tunnels. It is possible that ventilation will also be required during normal operation in the tunnels as well as the stations.

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Fire heat release rates are an important criterion used to design tunnel emergency ventilation systems and to test the appropriateness of the system response (ensuring safe evacuation of patrons from the facilities). It is considered a valid assumption that fire will be the governing criterion for the size of the primary ventilation infrastructure for a BRT tunnel. In this regard, and on the basis of a preliminary assessment of the vehicle engine types, all of the vehicle choices are similar and significant change in the size of the emergency ventilation plant is not anticipated based on vehicle engine choice alone. Note:

• The CNG vehicle has a slightly higher estimated fire size due to the larger quantity of combustible material. The difference is +15% in the fire heat release rate. It is recognized though that compressed gas represents a complexity requiring further study, due to the potential explosive nature of the gas tanks, and the unknown rate of the vehicle fire growth.

• Hybrid vehicles will be more efficient, and for the same range there exists the potential to reduce the onboard fuel. Considering however that the diesel itself represents only 25% of the assumed design fire size, this will not result in a large reduction in the ventilation plant requirement.

A summary of the ventilation implications (both operational and emergency) associated with BRT vehicle engine choice are given below:

• The size of the emergency ventilation plant will likely be similar for all four vehicle engine options. Further investigation will be necessary to more accurately estimate the peak fire heat release rate and fire growth associated with the selected vehicle.

• The presence of combustion engines, for ECD and CNG, introduces pollutants in the tunnels and stations. It is considered likely that mechanical ventilation will be required during normal and/or congested bus operations to provide sufficient control and removal of contaminants. This may consist of operating the emergency/primary ventilation systems at a reduced mode, or may require that discrete ventilation be available in the stations. Normal mode operation will result in higher costs due to power and maintenance.

• Mechanical ventilation may be required for normal/congested operation to ensure adequate removal of heat from all vehicle choices (such as engines and air conditioning) and to provide sufficient air exchange for passengers and employees. For ECD and CNG this would be combined with the pollutant control requirement. For electrically driven vehicles this may mean some operation of system fans, however the requirement will certainly be less than that for buses equipped with ICEs.

• The ventilation system will need to be designed for the ultimate peak fire size considering both the BRT and the Phase 3 rail vehicle technology.

Preliminary assessments of the tunnel ventilation system requirements have been performed by Earth Tech. Assuming a single bored tunnel with a central dividing wall, jet fans would not be required in the running tunnels (such a single bored tunnel is the assumed tunnel configuration, as discussed below). If twin bored tunnels were implemented, ventilation requirements may be different.

The conceptual tunnel ventilation system would require fan plants to be located at each end of underground stations and at tunnel portals. For longer sections of tunnel, ventilation shafts may be required at intermediate locations. Based on the design criteria and assumptions, none of the alignment alternatives identified below would require ventilation ducting within the running tunnels.

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Initial assessment of vehicle technologies for the Urban Ring Phase 2 Project, based on the tunnel ventilation requirements and capital and operational and maintenance costs, indicate that the currently preferred technology is hybrid electric. If MBTA buses other than hybrid electric vehicles are to use the tunnel then this could impact the tunnel ventilation design.

(ii) Tunnel Lighting

Road tunnel lighting designs should be prepared as required to meet the latest edition of “Recommended Practice for Tunnel Lighting” (RP-22). This standard identifies the minimum levels of lighting to be achieved at the tunnel entrance through zones referred to as threshold, transition and interior zones, located from the portal to the inside of the tunnel. The object of the road tunnel lighting is to enable traffic to travel safely through the tunnel. This is best achieved by providing the tunnel user with sufficient lighting to be aware of the road and to see any vehicles and obstructions ahead. Tunnel lighting is not expected to be a controlling factor in the layout of the tunnel cross section or tunnel alignments.

(iii) Electrical and Safety Equipment

The various tunnel systems will require a supply of power. Depending on the power requirements and the length of the tunnel sections, there may be a need for high voltage distribution within the tunnel with sub stations to step-down to low voltage supply over each section of the tunnel.

Safety equipment within the tunnel may include:

• Monitoring and supervision – Supervisory Control And Data Acquisition (SCADA);

• Communications;

• Closed Circuit Television;

• Traffic control; and

• Fire detection, fire suppression and fire fighting systems and equipment.

(iv) Drainage

The drainage system would consist of longitudinal drains feeding sumps which are discharged by pumps to the stormwater drainage system via an interceptor to separate pollutants from spillages. The drainage system would be located under the roadway surface. Cross-drains and sumps would likely be located at the tunnel portals to intercept water running down the tunnel portal approach ramps. Sumps would be required at low points in the tunnel alignment. The roadway surface would be designed to accommodate the drainage system requirements and the drainage system would be specified to deal with inflow of rainfall at the portals, groundwater seepage, accidental spillage and cleaning up, routine wall washing and fire fighting.

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(v) Operation

A tunnel control center will likely be required to ensure the safe operation of the bus tunnels. This facility could be incorporated within the station architecture or within some other part of the Urban Ring Phase 2 operational facilities.

An additional consideration during the operation of the tunnels is the scenario of a disabled vehicle within the tunnel. The method of recovery of the vehicle would ideally be timely and would minimize potential disruption to BRT services within the tunnels.

The current assumption is that the Urban Ring Phase 2 BRT service will adopt the use of 60-ft articulated buses. The nature of these vehicles is such that they must be towed from the front in the normal direction of travel; they cannot be pushed from behind. The method of recovering a disabled vehicle would normally require the recovery vehicle to reverse into position to tow the disable vehicle out of the tunnel. The distance over which the vehicle must reverse greatly increases the time taken to remove the disabled vehicle from the tunnel. Therefore, reducing the distance over which a recovery vehicle must reverse is one way to improve the efficiency of vehicle recovery. The ability to cross from one lane (or tunnel bore) to another either continuously or at regular intervals along the alignment can reduce the reversing distance.

3.1.5 Fire Life Safety

The fire life safety and fire protection of the tunnel require assessment of and planning for the following features:

• Emergency egress;

• Emergency ventilation;

• Fire protection of structures;

• Fire detection, fire suppression, and fire fighting equipment and systems;

• Communication systems;

• Traffic control;

• Drainage; and

• Emergency response plans.

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The key criteria at this stage are the emergency egress requirements for road tunnels1, which state that the

spacing between emergency exits should not be more than 1000-ft. Where tunnels are divided by a

minimum of 2-hour fire-rated construction or where the tunnels are in twin bores, cross passageways can

be used instead of emergency exits. Cross passageways should have a maximum spacing of 656-ft. The

impacts of these requirements on different tunnel configurations is discussed in Section 3.3.2. The

emergency ventilation requirements are also an important element in the development of options and this

is discussed in Section 3.1.4.

Fire protection of the tunnel structures is important to minimize fire damage, thereby reducing the risk of

structural failures or collapse, and minimizing the duration and cost of tunnel closures while necessary

repairs are carried out after an incident. The tunnel structures and the tunnel systems should be protected

against fire damage. In concrete structures, adequate concrete cover over steel reinforcement members

should be provided, and polypropylene monofilament fibers or fire protection boards should be considered

to minimize damage by concrete spalling. Fire resistant ducting for tunnel systems should also be

evaluated.

Fire detection systems and communication systems can typically be accommodated within the tunnel

structures without impacting upon the required tunnel cross section. The project team has determined that

there is potential for this accommodation at a conceptual design level; more specific details of these

systems would be developed at a later stage in design.

Safety management planning would assess a range of possible incidents in the tunnel (including

breakdowns, collisions, and fires) and determine the most efficient range of recovery and rescue measures

and procedures for emergency evacuation and intervention. It is likely that a control center would be

required to ensure the safe operation of the tunnel and to initiate and coordinate any rescue efforts.

The fire life safety provisions, tunnel systems, and operation of the tunnel asset should be considered for

both BRT and rail operation during future design development once a preferred alternative has been

identified. The analysis will include an evaluation of costs for providing Phase 2 compatible systems

versus Phase 2 and Phase 3 compatible systems for: structural elements; loading; utility accommodation;

ventilation; lighting; electrical and safety equipment; drainage; utilities; stray current protection; and

roadway construction details to accommodate future installation of rail.

3.1.6 Security

The approach to security of an Urban Ring Phase 2 tunnel would start early in the preliminary engineering

phase and would be borne out through detailed vulnerability assessments and risk management methods.

The key steps toward securing such a transportation asset would be to:

• Identify the threats;

• Assess damage potential and consequences of threats;

• Assess a range of countermeasures;

• Cost estimation; and

1 Standard for Road Tunnels, Bridges, and Other Limited Access Highways, NFPA 502, 2004


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• Implementation.

There exist a number of means and methods to deter, detect, and defend against potential threats, such that the security of this asset could be protected. The MBTA Silver Line has already shown that such measures are necessary and effective in preventing unauthorized vehicles from entering transit tunnels: In April 2007 a Jeep Cherokee broke through a gate at the entrance to the Silver Line tunnel portal in South Boston but was subsequently stopped from proceeding through the tunnel when a metal barricade was raised from the roadway1.

Security design criteria for the Urban Ring Phase 2 busway tunnel should be developed during the preliminary engineering phase.

1 Massachusetts Bay Transportation Authority website:

http://www.mbta.com/about_the_mbta/news_events/?id=11463&month=4&year=07


3.2 Construction Methodology

There are a number of potentially feasible construction methodologies that could be used to construct the Urban Ring tunnels. The methodologies can be grouped into three main types: cut and cover tunnels (including the top-down method); sequential excavation method (SEM) mined tunnels with a sprayed concrete lining; and tunnel boring machine (TBM) bored tunnels. Each method has advantages and disadvantages and some are more suited to particular ground types and environments than others.

Any tunneling method will cause ground movements and the ground movements will be affected by tunnel depth, tunnel diameter, geology, and the quality of construction. Some methods produce larger ground movements than others, but in all cases building settlement assessments should be carried out as necessary to determine the potential for unacceptable movements. The outcome of the building settlement assessments should assist in determining the need for underpinning, ground treatment or other protective measures. The cost and disruption of such measures should be balanced with the cost and disruption of alternative construction methods.

3.2.1 Cut and Cover Tunnel

The cut and cover technique has traditionally been used for transportation links in Boston dating back to the 1890’s when the Green Line was constructed. Cut and cover construction will require earth support systems to be installed prior to the commencement of the main excavation. There are different methods that can be used to provide earth support, including: slurry walls; bored pile walls; and sheet pile walls. The selection of a suitable method will be made during final design, and will depend upon local conditions and the performance criteria that will be developed for each location. A typical clamshell grab for excavating slurry walls is shown in Figure 3.4.

Depending on the design of the earth support system either it will require a cast-in-place concrete permanent structure or the earth support system itself will provide the permanent structure. The majority of the structures would be located in areas where the use of groundwater lowering techniques during construction should be minimized or very carefully controlled. Ground treatment is likely to be required at the base of such excavations to reduce the insitu permeability and minimize groundwater flows. The tunnel structure is subsequently backfilled to restore the ground surface.

The traditional cut and cover method requires the ground to be open for the duration of construction and the main excavation takes place with full surface access. Typically, temporary propping is installed as excavation proceeds following by construction of the base slab, intermediate slabs, and finally the roof slab. The structure is subsequently backfilled to restore the ground surface. In urban environments, the use of the top-down method (i.e. installing the perimeter walls and roof prior to main excavation beneath) of cut and cover tunneling is advantageous over other cut and cover techniques in relation to minimizing impacts to the general public during construction. The top-down method requires installation of the perimeter walls and a roof deck prior to commencement of the main excavation. The roof deck allows traffic flows to be restored while construction takes place beneath.

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Cut and cover construction in close proximity to existing buildings is achievable with good control of ground movements. The main disadvantage is that the operation is potentially very disruptive, even when the top-down method is employed, as many of the operations will have to occur on the surface. Lane closures, utility diversions, temporary relocation of building access points, and diversion of traffic will be inevitable in most cases.

Figure 3.4: Typical Slurry Wall Equipment for Cut and Cover Construction

The major advantages and disadvantages of the cut and cover tunnel construction method with respect to planning a tunnel within the Urban Ring Phase 2 corridor are:

(i) Advantages

• Generally less expensive than underground tunneling methods for shorter lengths and relatively shallow depths because of simpler excavation methods;

• Generally shorter overall construction duration for shorter lengths of tunnel;

• Underground obstructions can usually be handled without excessive increases in cost and schedule;

• Flexibility in terms of horizontal alignments if other constraints allow (e.g. building foundations) and in tunnel cross section; and

• Construction in close proximity to existing buildings is achievable with good control of ground movements.

(ii) Disadvantages

• Major construction phase impacts and disruption due to open excavation, including lane closures, temporary relocation of building access points, and diversion of traffic.

• Impacts will be experienced along the full length of the tunnel due to open excavation;

Clamshell Trench Cutter/Hydromill


• Less economical for longer lengths of tunnel;

• Major right-of-way and property requirements for excavation; and

• Major utility diversions likely to be required.

3.2.2 SEM Mined Tunnel

The second construction method is mining the Urban Ring Phase 2 tunnels using SEM mined tunnels. The SEM method involves excavation of the tunnel using standard construction equipment. The tunnel is usually lined in two steps: An initial lining of sprayed concrete provides immediate support and a subsequent secondary or permanent lining is then placed using either sprayed concrete or cast-in-place concrete. A waterproof membrane is usually installed between the primary and secondary linings.

Figure 3.5: SEM Mined Tunnels Using Multiple Drifts

The SEM relies on the insitu ground having suitable properties to remain stable following excavation and until such time as the initial support can be placed – known as stand-up time. Where the stand-up time is insufficient, then additional ground pre-support methods or ground treatment methods are required to stabilize the excavation. In addition, the tunnel heading can be sub-divided into a number of smaller excavation headings to minimize the size of the exposed face, as illustrated in Figure 3.5. Timely closure of the tunnel lining ring is important in controlling ground movements and ensuring stability of the excavation.

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This option has the significant advantage that the cross section for the tunnel is not restricted to a circular shape as it is with a TBM tunnel. Use of non-circular geometry can lead to a more efficient section and therefore lower costs. Use of the SEM also allows more flexibility with the alignment. The main disadvantage of the SEM is that significant ground treatment may be required since the tunnel is not sealed off from the ground water pressure during construction as it is with a TBM driven tunnel.

On the recent Silver Line Phase 2 Russia Wharf project in Boston, the SEM was successfully used in conjunction with ground freezing. However, the length of tunnels was comparatively short (approximately 400-ft) and the approach used for Russia Wharf would not be practical for extended lengths of tunnel for the Urban Ring. Other forms of ground treatment are available that could be feasible, however detailed geotechnical investigation along the alignment would need to be carried out to determine their viability. If it is not possible to perform the ground treatment from the tunnel face, then significant surface disruption may be caused by the ground treatment process. Although use of the SEM may allow optimized tunnel cross section and reduced potential for ground movements, SEM tunnels can result in greater ground movements than for a TBM driven tunnel of similar cross sectional area.

The major advantages and disadvantages of the SEM mined tunnel construction method with respect to planning a tunnel within the Urban Ring Phase 2 corridor are:

(i) Advantages

• Flexibility in terms of horizontal alignments if other constraints allow (e.g. building foundations etc) and in tunnel cross section. The tunnel cross section does not need to be circular as for a TBM bored tunnel and this can lead to optimization of the tunnel cross section and reduced costs;

• Generally shorter overall construction duration for shorter lengths of tunnel;

• Underground obstructions can usually be handled without excessive increases in cost and schedule;

• Minimizes surface disruption as the majority of the construction work takes place below ground (with the exception of portal and station locations);

• Potential to limit the material handling (supply and removal) to discrete locations rather than the entire length of the tunnel if suitable shaft access sites can be found;

• Minimizes the need for utility diversions.

(ii) Disadvantages

• Significant ground treatment may be required to stabilize the excavation during tunneling, as the tunnel is not sealed off from the ground water pressure as it is with a pressurized face TBM driven tunnel;

• Less economical for longer lengths of tunnel; and

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• Shallow vertical tunnel alignments may result in ground movements that pose potential for structural damage to nearby buildings, thereby requiring protective works (e.g. compensation grouting).

3.2.3 TBM Bored Tunnel

The third construction method is TBM bored tunnels. This method entails the procurement of a custom-made TBM – a specialized and expensive piece of construction equipment. The TBM is then assembled within a cut and cover launch chamber at one end of the tunnel alignment from which it is launched to bore through the ground. The front of the TBM is equipped with a cutterhead on which a number of cutting tools are mounted. The cutting tools are designed to suit the geological conditions anticipated to be encountered during the tunnel drive. The cutting tools excavate the ground and the resulting excavated material is then removed from behind the cutterhead. The excavated material is transported back through the tunnel to the launch point where it can be raised to the surface and removed from the site by rail or by truck. As the tunnel is bored, reinforced precast concrete segments are installed behind the TBM to form the tunnel lining. The annular void between the outside of the segmental lining and the ground is filled with grout to ensure full contact between the ground and the lining and to minimize ground surface settlements.

The likely choice of TBM for the Urban Ring Phase 2 tunnels would be a pressurized face machine owing to the anticipated geology and the urban environment. There are two general categories of pressurized face machine: an earth pressure balance machine or a slurry machine. Both types of machine have the ability to maintain a positive face pressure to ensure stability of the ground during tunneling with the primary difference being the method used to achieve this face pressure.

The state of the art in TBM technology has advanced considerably over the last 10 years. Pressurized face TBMs can safely construct tunnels in soft ground conditions, while minimizing impacts on surrounding structures. Developments in cutterhead design mean that TBMs can be equipped to deal with variable ground conditions, from soft ground to hard rock. Machine diameters in the region of 50-ft have been manufactured to build urban tunnels in Spain (Madrid Calle M30) and in China (Shanghai Yangtze River tunnel).

A TBM tunnel also offers good ground movement control owing to the continuous grout injection process that fills the annular void between the back of the tunnel lining and the ground during the subsequent excavation cycle. Grouting operations would occur concurrently with advance of the TBM. Ground movements can be minimized through careful control of the tunnel face pressures and grouting pressures. Some disadvantages of a TBM are the large capital cost of the machine itself, which require a minimum length of tunnel to be constructed to be cost effective, and the restriction on turning radius.

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Figure 3.6: SMART Project Tunnel Boring Machine (43’-4” diameter)

The major advantages and disadvantages of the TBM bored tunnel construction method with respect to planning a tunnel within the Urban Ring Phase 2 corridor are:

(i) Advantages

• Efficient for longer tunnels – in terms of both cost and schedule – as economies of scale are realized for the capital investment in the TBM and precast concrete lining assembly;

• Good control of ground movements through the use of pressurized face TBMs with gasketted precast conrete linings and continuous grouting operations;

• Minimizes surface disruption as the majority of the construction work takes place below ground (with the exception of portal and station locations);

• Limits the material handling (supply and removal) to discrete locations rather than the entire length of the tunnel;

• Minimizes the need for utility diversions.

(ii) Disadvantages

• More expensive for shorter lengths of tunnel owing to the capital investment in the TBM and the precast concrete lining assembly;

• Dealing with underground obstructions can potentially be costly and time-consuming;

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• Shallow vertical tunnel alignments may result in ground movements that pose potential for structural damage to nearby buildings, thereby requiring protective works (e.g. compensation grouting);

• Horizontal tunnel alignments are potentially limited by the capability of the TBM (this can be mitigated through the use of short cut and cover sections to negotiate tighter horizontal radii);

• Tunnel material handling (supply and removal) will be concentrated in discrete locations. Although it is a benefit to avoid disturbance along the entire alignment, as would be the case for cut and cover tunneling, focusing the work in discrete locations will intensify the impacts as these points; and

• Changes in tunnel diameter are not achievable without other construction methods.

3.2.4 Initial Recommendations

The three tunneling methods were evaluated to determine which method or methods would be appropriate for the Urban Ring Phase 2 busway tunnel structures, given the requirements and constraints of the project and the corridor. The intent of this evaluation process was to make an initial recommendation of viable construction methods to be used for alignment alternatives analysis. The primary purpose of making this initial recommendation was to allow a more transparent comparison of the numerous alignment alternatives. This initial selection of construction methodology has not precluded the development of a viable alignment alternative. Indeed, some alternatives have required different construction methods to be employed and this is noted in the description of alternatives considered in Chapter 4.

Recommendation of a tunnel construction method should not be considered to preclude other methods from being considered during subsequent stages of the planning and design process. The decision on which construction methods to be used to build the preferred busway tunnel, including portals, running tunnels, and stations, remains open.

The final choice of running tunnel construction method and configuration will depend on the final busway tunnel alignment chosen; the geology and hydrogeology; the vertical alignment; the anticipated ground movements and building settlement assessments; and noise and vibration impacts on sensitive hospital and research operations. These issues will need to be addressed during subsequent engineering studies as more information becomes available.

(i) Tunnel Portal Structures

The tunnel portal structures will comprise an open cut approach ramp (“boat” section) and a covered tunnel section. The construction will most likely require temporary earth support systems to be installed to enable the construction of a cast in-situ concrete structure that provides permanent support.

The intrinsic nature of tunnel portals providing a transition from surface level into bored/mined tunnel requires the use of open cut and cut and cover tunnel techniques.

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(ii) Running Tunnels

The three construction methods described above were considered for the construction of the running tunnels. The evaluation of each technique and the selection of a viable method for current planning purposes is described below. Single bore or twin bore configurations can be achieved with any construction method and discussion of these configurations is presented later in this document.

The cut and cover method was not recommended for use in planning the Urban Ring Phase 2 running tunnels for the following reasons:

• Physical constraints and heavy traffic demand make it impossible to allow extended roadway closure on the principal Huntington Avenue – Longwood Avenue – Brookline Avenue tunnel alignment. Even if the open excavation period were minimized through phasing and expedited roadway restoration (which would increase costs), traffic on these roadways, and access to buildings, would still be severely affected for extended periods.

• Cut and cover construction would have major impacts on sensitive environmental and open space resources (in particular the Emerald Necklace parkway system) on and near the proposed tunnel alignment. Outside of the more environmentally sensitive zones, environmental impacts would still be significant (e.g. noise, dust etc.).

• Lack of available public right-of-way corridors for key components of the corridor would require significant land takings to allow cut and cover construction, resulting in additional cost and disruption.

• The cut and cover method could be appropriate for discrete lengths of some tunnel options where surface impacts would be more tolerable or where site constraints, alignment geometry, project requirements or other factors favor this method of construction.

The SEM mined tunnel method was not recommended for use in planning the Urban Ring Phase 2 running tunnels for the following reasons:

• The potential need for a significant amount of costly and time-consuming ground treatment could reduce potential benefits of shorter construction duration and minimized surface disruption. The very limited amount of geotechnical information currently available results in the SEM mined tunnel being at greater risk of significant cost increases at this stage in the project than does a TBM bored tunnel. This was a primary reason for choosing the TBM method at this stage in the planning process. Once further geotechnical information is available and the tunnel alignment is finalized, this decision should be reviewed.

• The significant lengths of some tunnel alignment alternatives do not favor construction using SEM for the entire length.

• SEM mined tunnel could be appropriate for discrete lengths of some tunnel options where changing cross sections are required or where site constraints, alignment geometry, project requirements or other factors favor this method of construction.

The TBM bored tunnel method was recommended for use in planning the Urban Ring Phase 2 running tunnels for the following reasons:

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• The TBM bored tunnel option offers the potential to minimize surface disruption and reduce environmental impacts. These are considerable benefits for any alignment alternative, but are of particular importance in the more densely developed sections of the corridor with heavy traffic demand. While this may be true also of the SEM mined tunnel, it will be heavily dependent on the extent and nature of ground treatment required.

• Pressurized face TBMs can safely construct tunnels in soft ground conditions, while minimizing impacts on surrounding structures. Developments in cutterhead design mean that TBMs can be equipped to deal with variable ground conditions, from soft ground to hard rock, and boulders. Machine diameters in the region of 50-ft have been manufactured to build urban tunnels in Spain (Madrid Calle M30) and in China (Shanghai Yangtze River tunnel).

• The majority of the tunnel alternatives are of sufficient length to enable a TBM drive to be an economically viable method.

• Consideration of environmentally sensitive zones (e.g. Emerald Necklace, Muddy River, and Charles River) would favor methods that do not require excavation from the surface or ground treatment methods.

Noise and vibration impacts relative to the SEM and TBM methods will required further assessment once geotechnical information is available and the extent and type of ground treatment has been better established. It is considered that the SEM will have noise and vibration impacts that would be either equal to or less than those created by TBM construction, however the major factors will be the geology and the method of removing excavated material from the tunnel (e.g. truck, rail, or conveyor).

As a result of this review, it was determined that TBM construction was an environmentally acceptable solution offering the potential to minimize disruption and provide the most cost-effective approach for the planning of the Urban Ring Phase 2 running tunnels.

(iii) Underground Stations

Alternatives for station construction using cut and cover, the SEM, and TBM methods were investigated. The selected method would depend on a number of factors, including the location of the station, the site constraints, and the geology and groundwater conditions.

The use of an over-sized TBM which would accommodate station platforms was rejected owing to spatial constraints, right-of-way issues, impacts on portal structures and difficulties converting to Phase 3 rail use, as discussed later in this report. The SEM method is a viable solution, and can reduce surface impacts. However, the SEM method will still require two large shafts at each end of the station to accommodate ventilation equipment and vertical circulation elements. Given the lack of geotechnical information, the desire to keep the stations relatively shallow, and the relatively short length of the stations, it was considered prudent at this stage in the planning process to adopt cut and cover for the full length of the station.

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Traditional cut and cover or the top-down method, where the main excavation occurs below a temporary roof deck, are both viable methods for the station construction. The current thinking is that in the densely developed and heavily trafficked areas such as the LMA, the top-down method would help to minimize disruption to the surrounding communities. The increase in cost and construction duration associated with this method need to be balanced with the perceived minimization of disruption.

3.3 Typical Tunnel Cross Sections

The principal tunnel elements comprise the portals, the running tunnels, and the stations. Typical cross sections for the principal tunnel elements have been developed taking into account the design criteria outlined in Section 3.1.

The tunnel cross sections have been developed for the Phase 2 BRT requirements and subsequently checked to confirm whether or not Phase 3 light rail and heavy rail requirements can be accommodated within the bus tunnel cross section. Excepting the rail, traction power, and other systems, the primary structural differences in cross-sectional requirements between Phase 3 light rail and Phase 3 heavy rail are the vertical clearances required (see Figure 3.3), and the walkway requirements (the light rail walkway is low-level, whereas heavy rail may require an elevated walkway).

It was shown that the BRT clearance envelope requirements were the controlling factor in determining the tunnel cross sections, and that the clearances for rail can be easily accommodated by any tunnel construction method. Therefore there is no cost premium associated with protecting future conversion to rail with respect to tunnel cross section. Further refinement to the BRT vehicle envelope in subsequent engineering studies may afford a reduction in the tunnel cross section.

3.3.1 Tunnel Portals

The tunnel portals will comprise a tunnel portal approach ramp (open cut “boat” section) and a cut and cover tunnel section down to the tunnel eye. Typical cross sections through a tunnel portal approach ramp (with walkway niches) and a cut and cover tunnel section (without walkway niches) are presented in Figure 3.7 and Figure 3.8.

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CL STRUCTURE

CLSYMMETRICAL ABOUT

EXISTINGGROUND LEVEL

4'-0

"

CAST-IN-PLACECONCRETE

PARAPETWALL

WALKWAY

12'-0"

CL

2'-0"

TEMPORARY EXCAVATIONSUPPORT SYSTEM

ROADWAYSURFACE

14'-6

"

7'-6

"

NICHE(1'-0" DEEP)

LANE CL LANE

15'-0" 2'-0"

VAR

IES

Figure 3.7: Typical Cross Section – Tunnel Portal Approach Ramp

CL

14'-6

"

LANE

12'-0"3'-0"

CL LANE

17'-6

"4'

-0"

3'-0

"

CL TUNNEL

CLSYMMETRICAL ABOUT

1'-0"

1'-6"

3'-0"(TYP.)

VAR

IES

ROADWAYSURFACE

EXISTINGGROUND LEVEL

WALKWAY

CAST-IN-PLACECONCRETE

Figure 3.8: Typical Cross Section – Cut and Cover Section

At the tunnel eye, where the running tunnels are to connect into the portal, there may be a need for additional ground treatment as the ground cover is usually relatively shallow at this location.

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3.3.2 Running Tunnels

As discussed in Section 3.2, there are a number of different tunneling techniques that can be used to construct the running tunnels and of these methods, the TBM bored tunnel method was recommended for use in planning the Urban Ring Phase 2 running tunnels. TBM construction can be configured to provide either a single tunnel carrying two lanes separated by an internal dividing wall or two tunnels each carrying one lane. Cross sections for twin bored tunnels (Figure 3.9) and a single bored tunnel (Figure 3.10) were developed.

(i) Twin Bored Tunnels

Some potential benefits of the twin bored tunnel solution compared with the single bored tunnel may include:

• Reduced ground surface settlements;

• Reduced cost for bored tunnels (although the savings may be offset to a degree by the stations being deeper where the twin bored tunnels are vertically separated and provisions of egress shafts or cross passages or both);

• Reduced volume of excavated material;

• Shorter portal structures as the tunnel diameter is less than for single bore and the resulting amount of ground cover above the tunnel at the tunnel eye is therefore less; and

• Higher utilization of the space formed within the tunnel.

CL TUNNEL

CL LANE CL LANE

12'-0" 3'-0"

14'-0"

14'-6

"6'

-1"

Ø25'-1

1"

77'-9"

1'-3"

CL TUNNEL

ROADWAYSURFACE

WALKWAY

PRECAST CONCRETETUNNEL LINING

CROSS PASSAGE

Figure 3.9: Typical Cross Section – Twin Bored Tunnels

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Twin bored tunnels with connecting cross passages, as shown in Figure 3.9, require the two tunnels to be positioned at a similar elevation. The available horizontal corridor width is heavily constrained along key portions of the alignment such that twin bored tunnels would need to be vertically separated and may require vertical shafts to provide emergency escape facilities.

(ii) Single Bored Tunnel

The potential benefits of a twin bore approach are outweighed by the benefits of the single bore tunnel and the challenges facing the twin bore approach in the Urban Ring Phase 2 corridor. The principal reasons for this are presented below.

• The public right-of-way corridors are narrow along key parts of the alignment, particularly Longwood Avenue and Brookline Avenue where the minimum width between buildings is approximately 50-ft and 60-ft, respectively. A single bored tunnel would have a smaller plan footprint width (approximately 42-ft) than twin bored tunnels positioned side by side (approximately 78-ft for twin 26-ft diameter tunnels and one diameter of ground between tunnels). Even if ground cover between the twin bored tunnels could potentially be reduced to 10-ft, the resulting plan footprint width would be approximately 62-ft;

• Although twin bored tunnels could be vertically separated to reduce the plan footprint (to approximately 26-ft), this would potentially limit the flexibility to use cross passages for a means of egress, and may require escape shafts to be constructed to ensure that the distance between egress points is no greater than 1000-ft (as per the requirements of NFPA 502, Standard for Road Tunnels, Bridges, and Other Limited Access Highways, 2004). Where cross passageways are provided, these should have a maximum spacing of 656-ft. Vertical separation of the twin bored tunnels would place additional constraints on the tunnel alignments to enable the transition from a horizontally separated position to a vertically separated position;

• Twin bored tunnels have the potential for greater construction phase impacts both spatially because they would create a wider plan footprint and escape shafts may be required, and temporally because the bores would be made either sequentially using one TBM or concurrently using two TBMs with a lag between the drives;

• The use of a single bored tunnel with a dividing wall potentially allows more flexibility in BRT operations in the case of a disabled bus in the tunnel. The articulated buses cannot be pushed from behind, they have to be towed from the front. In the single bored tunnel, access doors could be located within the central wall that would allow a rescue vehicle to cross from one roadway to the other to rescue a disabled vehicle. These access doors would limit the length of tunnel through which the rescue vehicle must reverse, and may reduce the time taken to clear the tunnel of the disabled vehicle and restore normal service. Provision of such access doors would require careful consideration of NFPA requirements, fire life safety issues, and protection from errant vehicles. One way of effecting the recovery is outlined below:

o The closest central access doors located both in front of and behind the disabled vehicle would be opened.

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o The recovery vehicle would enter the tunnel using the blocked lane, while BRT service can remain in operation in the opposite lane.

o When the recovery vehicle reaches the central access door behind the disabled bus, the BRT service in the opposite lane would be temporarily suspended for a short period of time to allow the recovery vehicle to pull out into the opposite lane, pass the disabled vehicle, and then return to the blocked lane in front of the disabled vehicle through the next central access door.

o Once the recovery vehicle has returned to the blocked lane, the BRT service in the opposite lane would resume and the recovery vehicle can tow the disabled bus out of the tunnel.

o Depending on the spacing of the central access doors, the length of tunnel through which the recovery vehicle would need to reverse will be relatively short, thereby reducing the length of time taken to restore normal service.

• The single bored tunnel could potentially provide increased flexibility in Phase 3 with regard to providing track crossovers. A length of the central dividing wall would be removed to install the necessary switches and crossings to allow trains to cross from one track to the other, although this would need to be verified in relation to the ventilation strategy for the particular section of tunnel. This could reduce the extension of station excavations. It should be noted that vertically stacked twin bored tunnels would preclude the installation of crossovers;

• There is the possibility to include drainage sump structures within the main tunnel rather than creating separate enlargements, as would likely be required for a twin bored tunnel solution with low points in between stations;

• There is an opportunity to include revenue generating utilities within a service corridor below the road deck; and

• Narrower and deeper TBM launch and reception points compared with twin bored tunnels side by side.

Given the large number of tunnel options being investigated, it is most efficient and understandable to evaluate them based on a single tunnel construction method for the purposes of comparison.

For the reasons described above, a single bore TBM tunnel is expected to be the most suitable and cost-effective tunneling method for the Urban Ring Phase 2. At the same time, the project team has taken care that the proposals remain somewhat flexible with respect to alternative alignments, tunnel configuration, and methodologies. As a result, the alignment alternatives were primarily developed on the basis of a single bored tunnel.

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ROADWAYSURFACE

CL LANE CL LANE

WALKWAY

CL TUNNEL

Ø41'-10"

DIVIDING WALL12'-0"

14'-0"

3'-0"

PRECAST CONCRETE TUNNEL LINING

BACKFILL CONCRETE

TUNNEL DRAINAGE & SYSTEMS(POTENTIAL UTILITY CORRIDOR)

14'-6

"11

'-2"

Figure 3.10: Typical Cross Section – Single Bored Tunnel

Over-Sized Single Bored Tunnel. Consideration has been given to the possibility of constructing the running tunnels using an over-sized TBM (approximately 50-ft excavated diameter), such that an upper deck and a lower deck could be built within the bored tunnel. This would allow the construction of station platforms within the single bore and would provide flexibility in the location of station platforms (i.e. anywhere that the tunnel alignment meets the horizontal and vertical curvature requirements for a station). Off-line vertical circulation and ventilation shaft structures can then connect to the bored tunnel through mined tunnels.

It is acknowledged that this solution has potential benefits with relation to reducing surface construction works and providing the flexibility to locate – and extend, for Phase 3 – station platforms. However, such a solution has not been adopted at this stage, for the following reasons:

• Increasing the size of the TBM will require longer and deeper portal structures. The diameter of the single bored tunnel solution has been kept to the minimum required dimension for this reason;

• The public right-of-way corridors are narrow along key parts of the alignment, particularly Longwood Avenue and Brookline Avenue where the minimum width between buildings is approximately 50-ft and 60-ft, respectively. The diameter of the single bored tunnel solution has been kept to the minimum required dimension for this reason but will likely require underpinning and ground treatment works. Enlarging the tunnel diameter will potentially significantly increase building foundation conflicts and underpinning and ground treatment works depending on the final alignment selected;

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• Providing the grade separation required for the two-deck approach would either require further extension of the tunnel portals, or more complex construction within the bored tunnel itself. Where underground stations are located in close proximity to portals, this grade separation may not be achievable over the distance available; and

• Potential future conversion to Phase 3 rail would be more complicated and costly at the locations where the future Phase 3 tunnel would connect into the Phase 2 tunnel than for a smaller diameter single bored tunnel (without the two-deck approach) or for twin bored tunnels.

It is considered that the use of a large diameter running tunnel that can accommodate station platforms would be more suited to the initial construction of a rail transit system rather than for a BRT system that can accommodate potential future conversion to rail. The option to provide a larger diameter single bored tunnel with two decks – an upper deck for BRT, fitted out during Phase 2, and a lower deck provided during Phase 2 and fitted out for rail during Phase 3 – was also assessed, but rejected for similar reasons.

Therefore the tunneled alternatives have, in general, been developed on the basis of a single bored tunnel of approximately 42-ft diameter. The minimum horizontal turning radius for the TBM has been assumed to be 700-ft (the Stormwater Management and Road Tunnel in Malaysia used a 43-ft diameter TBM which was designed to negotiate a 660-ft radius). Although this could potentially be reduced depending upon, among other factors, the diameter of the machine and the design of the backup gantries, it is unlikely to be reduced to the extent that the alignment options developed would change significantly i.e. a smaller diameter TBM that can accommodate single lane traffic is unlikely to be able to negotiate a 150-ft radius curve. At present, the vertical curves in the bored tunnel are compatible with heavy rail criteria and are generally in excess of 6000-ft – this is considered to be well within the limits of the TBM maneuverability.

(iii) Tunnel Boring Machine Launch and Reception Areas

At the launch point for the TBM, there would need to be sufficient space for the following main tunneling operations and facilities:

• TBM assembly;

• Storage of tunnel segments;

• Grout batching plant;

• Storage of TBM consumables and supplies;

• Logistics to enable supply of tunnel segments to the advancing tunnel face;

• Removal, storage and handling of excavated material (may require slurry separation plant if a slurry TBM is selected for tunnel construction); and

• Site offices and support facilities.

The reception point for a TBM will require a suitably sized reception shaft or chamber into which the TBM can be driven, for subsequent disassembly and removal.

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Several of the alignment alternatives that have been developed have limited space for launching and servicing a TBM to drive the running tunnels. Potential construction staging areas have been identified for the various alignment alternatives that are considered to provide the minimum required space for this function. Although the staging areas may not be ideal in terms of their size and layout, it is not uncommon in the tunneling industry to have to work from confined construction sites, as urban areas are increasingly seeking to exploit underground space while minimizing the impacts on the existing environment. Examples of constrained tunneling worksites can be seen in Figure 3.11.

Project: Weintal Collector Country: Austria Use: Wastewater TBM Type: Earth Pressure Balance Geology: Clay, silts and sand Diameter: 28’-3”

Project: Lake Thun Flood Relief

Country:

Switzerland

Use: Flood Relief

TBM Type:

Mixshield

Geology: Gravel, sand and silt

Diameter:

20’-7”

Figure 3.11: Examples of Constrained Tunneling Worksites

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3.3.3 Underground Stations

For current planning purposes, the conceptual design of the typical station is a cut and cover construction and requires a plan footprint of approximately 550-ft by 60-ft, with some local enlargements for vertical circulation elements. This structure includes allowance for the tunnel ventilation fans and damper layouts. However, a detailed assessment of associated mechanical and electrical equipment rooms, substations, communications, machine rooms, etc. has not been performed at this stage.

This typical station has been developed based on the most constrained site locations along Longwood Avenue that would require the station platforms to be end-loaded, thereby limiting the width of the station while increasing the length. Further refinements to station design on a location by location basis would be required in subsequent engineering studies to determine whether a more economical and efficient structure could be accommodated. The typical station layout is shown in Attachment A.


4 Alternatives Considered

A central consideration in planning for the proposed Urban Ring Phase 2 project is the provision of as much dedicated right-of-way (ROW), in the form of busways and bus lanes, as possible. Dedicated ROW is essential to providing high-speed and reliable service, especially in areas of heavy traffic congestion. Federal guidelines for BRT projects call for a minimum 50% of the project route to be in dedicated ROW. Maximizing the amount of dedicated ROW, and optimizing its efficiency and effectiveness, have been among the central focuses of the Urban Ring Phase 2 project team and the Citizens Advisory Committee (CAC).

The project team has tried to identify opportunities for dedicated ROW on surface busways and bus lanes wherever possible. However, there are some locations in the corridor where high levels of traffic congestion and physical constraints on available ROW have limited the opportunities for surface busways and bus lanes. In response to these constraints, the project team has reviewed the anticipated ridership benefits, costs, and impacts of a range of tunnel alternatives.

The primary objectives of the tunnel alignments are to:

• Reduce transit trip times;

• Increase quality and reliability of service; and

• Minimize impacts of surface transit operations in sensitive locations, especially on the pleasure-vehicle-only segments of the Emerald Necklace parkways.

The tunnel alternatives that have been analyzed encompass a significant range of lengths, number of underground stations, connections, and costs. However, all of the options include tunnel segments beneath the Longwood Medical and Academic Area (LMA). This is because the LMA is a critical activity center with a combination of characteristics that create the greatest challenges for surface BRT connections: it has a very high density of travel demand, a limited roadway network, significant traffic congestion, and limited opportunities for roadway expansion or new roadway connections. In addition, it is bounded on the north by the Fenway, a pleasure-vehicle-only parkway that is a component of the Emerald Necklace park system.

The proposed tunnel options all follow the general Urban Ring Corridor alignment, and all include a segment beneath the LMA that would enable the Urban Ring Phase 2 BRT vehicles to avoid the most congested and space-constrained segments of the corridor while still serving the transit demand of the LMA. This results in a minimum tunnel segment extending from the vicinity of Ruggles Station in the southeast to beyond the Sears Rotary in the northwest. Beyond this segment, the tunnel options encompass a range of lengths, alignments, and connections.

The tunnel alignment alternatives have been developed and evaluated in three stages:

• Development Stage 1. This corresponds to the “Build Alternatives” that were developed in winter 2007 and evaluated in spring 2007. This includes a broad range of tunnel alignments, lengths, and connections.

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• Development Stage 2. This corresponds to a closer analysis of several of the Build Alternatives as they pass through the LMA. This analysis included a more detailed engineering analysis of several different tunnel alignments, tunnel portal locations, and cut and cover work areas.

• Development Stage 3. This corresponds to the “Hybrid Alternatives,” the stage of the alternatives analysis process which generated a narrowed-down set of options that include the most promising segments and elements from the Build Alternatives. These include Alternative H2(T), which entails a tunnel connection from the vicinity of Ruggles Station through the LMA to the vicinity of Yawkey Station/Kenmore Station. This stage of tunnel analysis also included a more detailed engineering analysis of several different tunnel alignments, tunnel portal locations, and cut and cover work areas.

The description below summarizes the basic design and engineering features of the various tunnel options that have been analyzed. These include alignment, horizontal and vertical curvature, physical constraints, capital costs of the tunnels and underground stations, and anticipated impacts, both temporary construction phase impacts as well permanent impacts from the proposed alignment. The discussion of these alternatives includes the full range of tunnel options. As the development stages described below illustrate, further efforts have been invested in the more promising alignment alternatives.

4.1 Tunneled Alignment Alternatives – Development Stage 1

The tunnel alignments that were developed in the “Build Alternatives” stage of the alternatives analysis included a very wide range of options. These were developed based on the project goals and technical constraints, in addition to significant consultation and input from the project CAC and other stakeholders. There were many suggestions and desired tunnel alignments articulated by various stakeholders. In order to be as responsive as possible to stakeholder aspirations and concerns, the project team added several new tunnel options to the alternatives analysis in this development stage. In the first stage, a total of six different tunnel alternatives were developed and evaluated.

These options captured a broad range of tunnel approaches, encompassing various tunnel lengths, alignments, and connections. These different options can be broadly classified into two categories – short tunnel options and long tunnel options. The short tunnel alternatives, which are included in the Build Alternative 3 “family,” begin immediately west of Ruggles Station (avoiding the cost of an underground connection with Ruggles Station), pass beneath the LMA, and extend to either Yawkey Station, the vicinity of the BU Bridge, or Allston Landing (depending on the option). However, all of the tunneled sections in the “short tunnel” family stay to the south of the Charles River. The reason for investigating short tunnel options is to try to maximize the benefits of a tunneled alignment by enabling the Urban Ring Phase 2 to avoid the worst of the congestion and physical constraints while minimizing the costs associated with tunnels and underground stations. The short tunnel options include Alternative 3, Alternative 3A, Alternative 3B, and Alternative 3C, described below.

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The longer tunnel alternatives, which are included in the Build Alternative 4 “family,” provide connection from the Melnea Cass Boulevard corridor, with an underground connection to Ruggles Station, beneath the LMA, to Allston and Cambridge, requiring bifurcations in the tunnel alignment and passing beneath the Charles River. The longer tunnel options would entail many more underground stations and greater overall complexity compared with the short tunnel options, resulting in significantly increased cost. The reason for investigating the long tunnel options is to explore whether or not the increase in benefits of longer tunnels (e.g. reduced travel times, increased ridership etc) would offset the additional cost compared with the short tunnel options. The longer tunnel options include Alternative 4 and Alternative 4A, described below and presented in Attachment B.

4.1.1 Alternative 3

Alternative 3 comprises two separate lengths of tunneled alignment: the LMA tunnel which would connect Ruggles to Yawkey, through the LMA; and the Mountfort Street tunnel which would link Mountfort Street with either the Boston University Bridge area or with Allston.

LMA Tunnel

The LMA tunnel would be located to the west of the existing Ruggles Station. The portal approach ramp would commence at Leon Street and descend in a westerly direction, parallel to Ruggles Street and along the existing Massachusetts Bay Transportation Authority (MBTA) right of way, in front of the Northeastern University residence halls. The tunnel portal – the transition between the open cut approach ramp and the cut and cover section – would be located to the east of Field Street to enable reinstatement of Field Street. The cut and cover tunnel would extend form the tunnel portal to a point immediately west of Parker Street, from which the bored tunnel would commence.

Construction of the Leon Street portal will be in a very constrained site, adjacent to Northeastern University residence halls and Ruggles Street. Preliminary worksite locations have been identified, as shown in Figure 4.12. It should be noted that not all of these sites would necessarily be required for construction of a portal in this location. The parking lot adjacent to the Sweeney Field would be required to construct the TBM reception chamber end of the portal. The Sweeney Field itself would not be used during construction.

The Leon Street portal would pass beneath the Stony Brook conduits, and a construction methodology would need to be developed to ensure the continuity of this utility during construction.

A section of tangent, level track would be provided along Huntington Avenue to accommodate a cut and cover station in this location, in the vicinity of the Green Line “E” Branch station. Immediately after the underground station the bored tunnel would make a turn to align with Longwood Avenue, passing underneath the Mass Art building on the northern corner of the intersection of Huntington and Longwood Avenues.

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The preferred location for the Huntington Avenue station is assumed to be as close as possible to the intersection between Huntington and Longwood Avenues. Therefore the station would be located at the southern end of the length of tangent track beneath Huntington Avenue, placing the southern end of the platform approximately 450-ft from the intersection. Headhouse locations would be configured to facilitate convenient connections with the Green Line “E” Branch station located at street level.

A construction access shaft for top-down construction could be located in the Wentworth Institute of Technology parking lot off Vancouver Street, with the parking lot providing space for the construction worksite for Huntington Avenue station. Any construction works in this area will need to consider the MWRA pumping station and shaft, as shown in Section 2.6. [Note: Wentworth Institute has since indicated plans to develop the parking lot site with a new campus building.]

Figure 4.12: Leon Street Portal Worksites

The bored tunnel would generally follow the existing alignment of Longwood Avenue from Huntington Avenue until a point near Binney Street towards the west. A section of tangent, level track would be provided through Longwood Avenue in the vicinity of Avenue Louis Pasteur to accommodate an underground station.

Foundation constraints limit the length of tangent track that can be provided through Longwood Avenue, and building constraints limit the location of a cut and cover station. Therefore the Longwood Station under this alternative would commence in the vicinity of Avenue Louis Pasteur and extend west beneath Longwood Avenue.

Ruggles Street

Ruggles Station Northeastern University

Potential worksite locations

Potential worksite location

Leon Street Parker Street

Field Street Tavern Road

Potential worksites shown are preliminary indications of sites that could serve as construction staging and laydown areas . Further work will be required to define these sites during preliminary engineering studies.


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For the Longwood station a construction access shaft would be located in Tugo Circle. The front lawn of Harvard Medical School would be required for construction worksite space, supported by additional worksite space at another location in the general area. Construction works in this area will need to account for the underground parking garage beneath the Harvard lawn.

Figure 4.13: Longwood Avenue (Avenue Louis Pasteur) Station Worksites

At Binney Street, the alignment would curve in a northerly direction to pass underneath the south-west corner of the Shapiro Center and Brookline Avenue and connect with an alignment that follows the existing path of Pilgrim Road. The turn from Longwood Avenue would likely require some underpinning and foundation modification works to the south-west corner of the Shapiro Center building.

From Pilgrim Road the tunnel would pass underneath the Muddy River and follow Brookline Avenue. The bored tunnel would terminate beneath Brookline Avenue, immediately to the north of Fullerton Street, and cut and cover tunnel would extend north along Brookline Avenue from this point to the intersection with Yawkey Way. From this intersection, the cut and cover tunnel would curve west into the Air Rights Parcel 7 development site, through an approach ramp structure and up to a station that would be at approximately the same elevation as the existing Yawkey Commuter Rail station. The BRT station would be aligned with the Commuter Rail station at Yawkey. A widened section of the Beacon Street overbridge would accommodate the BRT approximately parallel with the Commuter Rail, emerging to the west of Beacon Street.

Longwood Ave




The approach to Yawkey station would be constructed using top-down construction methods to minimize disruption to traffic flows. The TBM would need to be disassembled and removed from the reception chamber at Fullerton Street. The cut and cover tunnel and approach ramp through the Parcel 7 site would require close coordination with the developers of the site to ensure that an envelope is preserved through the foundations and sufficient space is maintained through the Air Rights Parcel 7 structure to enable construction and installation of the necessary structural support and operational equipment at this location.

The portal structure would require the use of an 8% gradient which is not preferred, but is within the maximum allowable limits. The depth of the potential future Phase 3 station beneath the Mass Turnpike is not controlled by the maximum operational gradient of the selected Phase 3 rail service, rather it is the consideration of providing sufficient ground cover to: the Mass Turnpike; the existing station structures at Kenmore Square; and the Muddy River conduit. The maximum operational gradient of the selected Phase 3 rail service will affect the gradient and length of the tunnel portal structure in Phase 2.

The combination of a steep grade with a tight turn through the portal is not preferable, however this alignment geometry is located close to a station where the BRT speeds should be low. The BRT route will be below ground in a cut and cover structure over this length, creating the opportunity to increase the line of sight by widening the cut and cover structure. The roadway will also be protected from the adverse effects of weather, helping to improve operational safety.

It is considered that although this solution is not ideal from an operational perspective it is achievable and would not preclude the development of a Phase 3 alignment underneath the Mass Turnpike with a Yawkey/Kenmore station. The assumed platform elevation for this Phase 3 station is EL -81.5, as per the MIS preliminary drawings.

Although much of the section of alignment between Brookline Avenue and Beacon Street would be at existing grade, the site is likely to be built up as part of the Air Rights Parcel 7 development proposals (by others) and, therefore, would be effectively underground.

The Beacon Street bridge would need to be temporarily propped and re-constructed in stages to lengthen the bridge span while maintaining a reduced traffic flow during construction. Particular attention would need to be paid to the Green Line tunnel, which runs parallel to and underneath Beacon Street in this location. The widening of the cut section immediately to the west of Beacon Street would require the closure of Mountfort Street during construction. Works adjacent to the railway with regard to lengthening the span of the Beacon Street bridge and widening the cut section will need to be carefully planned and executed to ensure the safety of the operational railway.

Assuming that the LMA tunnel terminates in the southeast near Leon Street and in the northwest at Brookline Avenue/Yawkey Station/Parcel 7, there is not adequate space for a TBM assembly chamber at either end of the tunnel. Therefore space for TBM assembly would need to found in an intermediate location, where a cut and cover TBM assembly chamber would be built. The TBM would be assembled and launched from this shaft to drive toward the Leon Street portal, where it would be disassembled, transported along the surface to the access shaft for re-assembly and launch, and subsequently driven to the Yawkey portal. The only feasible intermediate spot that could accommodate a cut and cover TBM assembly chamber in or near the alignment is Winsor School playing fields. This would have major impacts on Winsor School operations.

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Mountfort Street Tunnel – Boston University Bridge option

Build Alternative 3 entails a second tunnel segment intended to avoid the congestion in the vicinity of the

Boston University Bridge. The portal structure for the tunnel would be built in Mountfort Street, and it

would descend from existing grade level in a westerly direction down through an open approach ramp to a

cut and cover tunnel that would extend to a portal located within the surface parking lot of the BU owned

former Cadillac Building located on Commonwealth Avenue. The alignment would meet perpendicular to

Commonwealth Avenue, and such that an at-grade intersection would allow the BRT to cross

Commonwealth Avenue and continue over the Mass Turnpike to cross the Grand Junction Railroad

(GJRR) bridge, thereby allowing surface routing across the Charles River.

The Mountfort Street to Boston University Bridge tunnel would likely be constructed entirely using cut

and cover tunnel owing to its short length. This will require several staged closures of roads in the area to

allow the tunnel to be built. The use of top-down construction could be maximized to reduce disruption to

traffic. Works in close proximity to the railway will need to be carefully planned and executed to ensure

the safety of the operational railway. The car park area at the back of the Cadillac Building would be used

as the main construction worksite.

Mountfort Street Tunnel – Allston option

The portal structure in Mountfort Street would descend from existing grade level in a westerly direction

down through an open approach ramp to a cut and cover tunnel, with the bored tunnel commencing to the

east of St Mary’s Street. The bored tunnel would pass underneath the Mass Turnpike and roughly follow

the alignment of Storrow Drive before crossing underneath the Mass Turnpike viaduct to connect with a

portal structure in the CSX rail yard.

The Mountfort Street to Allston tunnel would require closure of Mountfort Street during construction of

the portal in this area, and this would also serve as the construction worksite for the portal. At the Allston

portal an area of the CSX rail yard would be required for the construction worksite to build the portal and

to provide space for the tunneling facilities and operations. To the east of the Allston portal, the Mass

Turnpike viaduct would need to be temporarily propped and the existing piled foundations would need to

be modified to accommodate passage of the TBM through this area.

The following are some of the major findings of the engineering analysis and evaluation of Alternative 3:

• Neither tunnel terminus (Leon Street or Yawkey Station/Parcel 7) has optimal space or

configuration for a TBM launch chamber. This may require an intermediate location for a TBM

launch chamber, which would potentially require additional cut and cover construction, and the

efficiency of the tunnel boring operations would be reduced by requiring the TBM to be

assembled, launched, received, and disassembled twice instead of once.

• The Mountfort Street tunnel options would be expensive and disruptive, and would not provide

major travel time, ridership, or abutter benefits.


• The Brookline Avenue/Yawkey Station/Parcel 7 tunnel portal would be difficult to build, would cause major construction phase traffic disruption on Brookline Avenue, and would have permanent impacts on the Parcel 7 development and the future development potential of the parking lot site on the west side of Brookline Avenue opposite Yawkey Way.

• The proposed connection beneath Beacon Street between Yawkey Station/Parcel 7 would have impacts on the design and construction of the Yawkey Station improvements and the Parcel 7 development.

4.1.2 Alternative 3A

Alternative 3A would eliminate the Mountfort Street tunnel options in Alternative 3 and replace them with surface routing. The LMA tunnel, extending from Leon Street to Yawkey, would be the complete extent of tunneling under Alternative 3A, and would follow the same alignment as the LMA tunnel described in Alternative 3.

Alternative 3A has been developed to eliminate the cost and disruption caused by constructing either of the Mountfort Street tunnel options in Alternative 3, and minimize the length of tunnel while still achieving the bulk of the tunnel benefits.

The construction issues for Alternative 3A are the same as for the LMA tunnel of Alternative 3.

4.1.3 Alternative 3B

Alternative 3B is intended to address many of the challenges and issues of Alternative 3. Like Alternative 3A, Alternative 3B eliminates the Mountfort Street tunnel options and their associated cost and disruption. Additionally, Alternative 3B is intended to:

• Minimize the impacts upon the air rights Parcel 7 development and Brookline Avenue by relocating the position of the northern portal; and

• Minimize the impact to Beacon Street traffic flow by avoiding reconstruction of the Beacon Street bridge.

The Mountfort Street tunnel options of Alternative 3 are instead replaced with surface routing for these sections. The tunnel alignment from Leon Street through Longwood Avenue to Binney Street would be common with the LMA tunnel described in Alternative 3. At Binney Street the alignment would depart from the Alternative 3 route and curve to the north underneath the playing fields of the Winsor School, the Riverway and the Muddy River before rising up to a portal structure located parallel with the Green Line “D” Branch at Fenway Station (no station would be provided here), in the vicinity of Park Drive. The alignment would surface at Miner Street and allow surface BRT routing through the proposed Air Rights Parcel 7 development and to connect with Yawkey Commuter Rail.

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The construction issues for Alternative 3B are similar to those for the LMA tunnel of Alternative 3, with the following exceptions:

• The bored tunnel would pass beneath the Winsor School and the Emerald Necklace. However, the TBM would be able to remain underground for the length of its alignment, and would have no surface impacts to the Winsor School or the Emerald Necklace. The alignment would extend to a portal located in the abandoned rail freight spur adjacent to the Green Line “D” Branch and the Landmark Center;

• The abandoned rail freight spur/Landmark Center portal location affords adequate space for a TBM assembly chamber. This would eliminate the need for an intermediate cut and cover TBM assembly chamber at a location such as the Winsor School;

• The portal structure will require working in close proximity to the Green Line “D” Branch, a retaining wall for the Green Line portal and the side of the Landmark Center. Construction will need to take place beneath the Park Drive bridge, utilizing low-headroom construction equipment, and ensure that the foundations of the bridge structure are not compromised (see Figure 4.14); and

• Future Phase 3 construction would require establishment of a cut and cover structure to create an underground chamber to receive and disassemble the future Phase 3 TBM. This construction could be done during Phase 2, or at a later time, including during Phase 3 construction. However, it is important to ensure that there is adequate space in a suitable location. The most suitable location would be beneath the Winsor School playing fields. However, this surface impact would only be required if and when Urban Ring Phase 3 were built.

The construction of the abandoned rail freight spur/Landmark Center portal will have temporary impacts on the Landmark Center car park (and possibly access to the units on the western side of the shopping center), the Parks and Recreation buildings located adjacent to the Green Line “D” Branch Fenway Station, and the Children’s Hospital parcel between Munson Street and Maitland Street (currently used as a parking lot).

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Landmark Center


Park Drive

Green Line “D” Branch tracks

Green Line “D” Branch portal

Emerald Necklace

Beacon Street

Sears Rotary


Figure 4.14: Abandoned Rail Freight Spur / Landmark Center Portal

4.1.4 Alternative 3C

Alternative 3C takes the two-tunnel concept of Alternative 3 and effectively connects the tunnels into one slightly longer overall tunnel. The objectives of this alternative are to:

• Eliminate the need for additional tunnel portals by extending the length of bored tunnel; and

• Minimize the impacts upon the air rights Parcel 7 development by reconfiguring the proposed location of the station at Yawkey.

The tunnel alignment from Leon Street through Longwood and up Brookline Avenue to Yawkey Way would be common with the LMA tunnel described in Alternative 3. From Brookline Avenue and partially beneath the Mass Turnpike, there would be provision for a deep underground station. Towards Commonwealth Avenue the alignment would make a sharp turn to the west to align with Commonwealth Avenue and would head toward to the Boston University Bridge. There would be a split portal arrangement: one leg of the tunnel would create a portal starting beneath the BU Academy, passing beneath the BU Bridge to the roughly triangular plot of land in order to accommodate a surface route across the Grand Junction Railroad bridge; the second leg of the tunnel would continue underground out to Allston. It should be noted that such a split portal arrangement is challenging in terms of both construction and operations, given the rapidly changing grades, lane separation, and horizontal curves.

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The construction issues for Alternative 3C are similar to those for the LMA and Mountfort-Allston tunnels of Alternative 3, with the following exceptions:

• The interface with Parcel 7 is almost completely removed as the tunnel now passes beside the development, rather than through it.

• No reconstruction of Beacon Street bridge is required.

• A mined station tunnel underneath the Mass Turnpike would be built. This would be an expensive and more risky undertaking than the station in the Parcel 7 site.

• Construction of the split portal at the Boston University Bridge site would be challenging given the very small worksite, although access to the CSX rail yard beneath the Mass Turnpike would provide a laydown and support area during construction. Disruption to the BU Academy would be inevitable.

• The TBM would be launched and serviced from the Allston portal. An additional section of cut and cover tunnel would be built at the sharp curve in the alignment on Commonwealth Avenue to allow the TBM to negotiate the tight radius at this location.

4.1.5 Alternative 4

Alternative 4, the first of the long tunnel options, comprises a bored tunnel that commences from Melnea Cass Boulevard and bifurcates to the south of Commonwealth Avenue to provide two routes, one to Allston and one to Cambridge.

The tunnel portal to the east of Ruggles Station would be located to pick up the proposed center median surface BRT route along Melnea Cass Boulevard. The tunnel would then pass beneath the existing boat section of Ruggles Station in an alignment approximately parallel to and to the north of Ruggles Street. A mined station would be constructed beneath the existing Ruggles Station. The proposed station would require shafts at each end for tunnel ventilation, mechanical and electrical equipment, and passenger access and egress.

The alignment then continues in bored tunnel to Huntington Avenue, where a section of tangent, level track would be provided to accommodate a cut and cover station in this location, in the vicinity of the Green Line “E” Branch station. Immediately to the south of the underground station the bored tunnel would make a turn to align with Longwood Avenue, passing underneath the Mass Art building on the northern corner of the intersection of Huntington and Longwood Avenues.

The preferred location for the Huntington Avenue station is the same as in Alternative 3.

The bored tunnel would generally follow the existing alignment of Longwood Avenue with a section of tangent, level track located at the intersection of Longwood and Brookline Avenues to accommodate an underground station. The alignment would continue in a westerly direction, passing beneath the Emerald Necklace and the Muddy River. A section of tangent, level track would be provided beneath the Muddy River to allow construction of a mined station beneath the river in the vicinity of the Green Line “D” Branch Longwood Station. The proposed mined station would require shafts at each end for tunnel ventilation, mechanical and electrical equipment, and passenger access and egress.

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The tunnel would follow approximately the alignment of Borland Street and cross beneath Beacon Street.

A section of tangent, level track across Beacon Street would accommodate an underground station in the

vicinity of the existing Green Line “C” Branch Hawes Street station. At the northern end of the proposed

station, a bifurcation would be constructed to allow routing west to Allston and north to Cambridge.

Allston Route

From the bifurcation point, the tunnel would follow the alignment of Cottage Farm Road to

Commonwealth Avenue. An underground station would be constructed within Commonwealth Avenue,

between St Paul Street station and Boston University West station on the Green Line “B” Branch. The

alignment would continue west beneath Commonwealth Avenue before turning north to pass beneath

Alcom Street and the Commuter Rail and CSX rail yard. An underground station could be provided

beneath a possible future commuter rail station in the existing storage area to the north of the rail tracks

and south of the I-90 toll plaza. The tunnel would pass beneath the toll plaza to emerge from a portal that

runs parallel and to the east of the houses along Windom Street to meet bus lanes along a future Stadium

Way.

Cambridge Route

From the bifurcation point, the tunnel would follow the alignment of Essex Street. An underground station

would be provided beneath Essex Street to the south of Commonwealth Avenue, before the tunnel

alignment heads beneath the Charles River to Cambridge. The portal in Cambridge would be located

relatively close to the river, immediately to the north of the Grand Junction Railroad west of Fort

Washington Park.

Key issues associated with the construction of Alternative 4 include:

• Construction of the Melnea Cass Boulevard portal would require temporary land take on either side of the boulevard to provide a construction worksite.

• Northeastern University are currently constructing a new hall of residence on the corner of Ruggles St and Tremont St. The tunnel would need to avoid the foundations of this building.

• Construction of the mined station beneath the existing Ruggles station boat section, with relatively shallow cover to the underside of the boat section, will require extensive ground treatment and support. The invert levels of the boat section will also require confirmation.

• Construction of Huntington Ave and Longwood Ave stations would be similar to Alternative 3.

• The construction of the Longwood Green Line “D” Branch station would be mined to attempt to minimize impacts on the Emerald Necklace and Muddy River. The shafts at either end and the mined tunnel would still have an impact on the Emerald Necklace and Muddy River. There is also very limited space for a construction worksite and adverse topography. Extension of the station to accommodate Phase 3 is likely to require land acquisition and possible building demolition.

• Construction of the station at Hawes Street will include the construction of a turnout. There will be a large temporary impact to the Amory Playground during open cut construction works as the area would be used for a worksite.


• Construction of the Boston University west station would be similar to Huntington Avenue station.

• Construction of West Station would require some of the storage tracks in the CSX rail yard to be temporarily closed or diverted to enable construction. Part of the rail yard would be used during construction as a worksite.

• The Allston portal would likely be a TBM launch point and so a relatively large area would be required to provide space for the tunneling facilities and operations.

• The new Boston University central station would be constructed in a very constrained residential area. The worksite would likely be located in the Cadillac Building car park and in the disused gas station at Essex Street. Impacts to the residences around this station would be inevitable.

• Construction of the Cambridge portal would be relatively simple given the availability of land on this side of the Charles River in the area of the portal. This would be a TBM launch site for the tunnel drive to the turnout location at Hawes Street station.

4.1.6 Alternative 4A

The second long tunnel option has been developed to explore the possibility of maintaining connectivity with the Green Line branches, as in Alternative 4, but with a reduced number of stations. Additionally, a longer length of tunnel in Cambridge would pass beneath the Red Line and portal onto or near Binney Street.

The alignment follows the same route as for Alternative 4 from Melnea Cass Boulevard through to Longwood Avenue. However at the western end of Longwood Avenue the tunnel follows Brookline Avenue. The location of the station on Longwood Avenue would therefore need to be near Avenue Louis Pasteur, as in the Alternative 3 alignment. From Brookline Avenue the tunnel would turn beneath Park Drive and an underground station would be provided beneath Park Drive to the south of Beacon Street. This station would allow connection with the Green Line “C” Branch St Mary’s Street station and “D” Branch Fenway station.

The tunnel would continue along Park Drive with a bifurcation at Mountfort Street to allow routing to both Allston and Cambridge.

Allston Route

From the bifurcation point, the tunnel would pass beneath the Mass Turnpike and follow the alignment of Commonwealth Avenue. An underground station would be provided in the vicinity of the Green Line “B” Branch Boston University West station. The tunnel would then follow the same alignment as the Alternative 4 alignment, with a potential station in the CSX rail yard and a portal in Allston.

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Cambridge Route

From the bifurcation point, the tunnel would pass beneath the Mass Turnpike and follow the alignment of

St Mary’s Street. An underground station would be provided in the vicinity of the Green Line “B” Branch

Boston University Central station. The tunnel would then pass beneath the Charles River to Cambridge

where it would generally follow the GJRR, with underground stations in the vicinity of Fort Washington

Park in Cambridgeport and Massachusetts Avenue/MIT. The tunnel would then pass underneath the Red

Line at Kendall Square and surface through a portal onto or near Binney Street.

Construction of Alternative 4A would be similar to Alternative 4 with the following main differences:

• Construction of Park Drive station would require use of the Landmark Center parking lot as a construction worksite. The station would be located between the bridge abutment of the Park Drive bridge over the Green Line “D” Branch and the cut and cover box section of the Green Line “C” Branch – this will be a challenging construction. For Phase 3 compatibility, the station would likely need to be deep enough that the extension to accommodate longer platforms would occur to the north as a mined tunnel beneath the Green Line cut and cover section.

• Construction of the turnout at Mountfort Street will require extensive ground treatment and will require close coordination with the Commuter Rail, with some work undertaken from within the railway property. The construction site would need to be located within the street, requiring closure of Mountfort Street or the end of Park Drive for a considerable period of time.

• Details of the foundations of the buildings to the north of the Mass Turnpike are not known, and the alignment has been developed to avoid the buildings on plan, where possible. This has required the use of tighter than desirable gradients from a tunneling perspective and from the perspective of conversion to heavy rail in Phase 3.

• The construction of the tunnel and portal by Kendall Square/Binney Street will need to be below the Red Line and avoid the building foundations in this area.



Preliminary ridership analysis and evaluation of cost and benefit indicated that the increase in ridership for the long tunnel options (Alternative 4-series) compared with the short tunnel options (Alternative 3-series) was marginal, but came at a greatly increased cost as a result of the considerable additional length of tunnel and increased number of underground stations. This, in combination with feedback from various public meetings, suggested that further development of the Alternative 3-series alignments was warranted, particularly in the LMA. The Alternative 4-series alignments remain viable options.

Sub-variants of Alternative 3A were developed and referred to as: Alternative 3A-1; Alternative 3A-2; and Alternative 3A-3, as discussed below and presented in Attachment B.

4.2.1 Alternative 3A-1

Alternative 3A-1 shares the same alignment as Alternative 3A from Leon Street/Ruggles Street, along Huntington Avenue, with an underground station on Huntington Avenue, and along Longwood Avenue until the intersection of Longwood Avenue and Binney Street. At this location, the 3A-1 alignment continues along Longwood Avenue before making a relatively tight turn (250-ft radius) at the intersection of Brookline Avenue and Longwood Avenue. A length of tangent track beneath the Winsor School playing fields allows a station to be accommodated in this location, before the alignment makes a second tight turn (250-ft radius) to connect with a Pilgrim Road alignment, and from this point follows the Alternative 3A routing along Brookline Avenue to a portal at Yawkey/Air Rights Parcel 7. The tight turns could not be constructed using a TBM and would require use of other construction methods. The tight turns in this option would limit Phase 3 flexibility.

The construction issues for Alternative 3A-1 are similar to those for Alternative 3A, with the following exceptions:

• As in Build Alternative 3, the portal locations at Leon Street and Yawkey Station/Air Rights Parcel 7 would not have adequate space for a TBM launch chamber. This would require an intermediate TBM launch chamber, assumed to be at the Winsor School playing fields, with the associated impacts and disruption as in Alternative 3. The TBM launch point beneath the Winsor School would be incorporated within the cut and cover station at this location;

• Locating the Longwood Avenue station beneath the Winsor School rather than by Tugo Circle would reduce disruption to Longwood Ave and minimize building access conflicts. However, this would cause serious disruption to the Winsor School; and

• The two tight turns required for this alignment would need to be constructed using either SEM mined tunnels or by extending the cut and cover tunnel for the adjacent station.

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Alternative 3A-2 shares the same alignment as Alternative 3A from Leon Street/Ruggles Street, along Huntington Avenue, with an underground station on Huntington Avenue, and along Longwood Avenue until the intersection of Longwood Avenue and Avenue Louis Pasteur (Tugo Circle). An underground station would be provided at this location, before the 3A-2 alignment follows the alignment corridor identified in the MIS by making an 800-ft radius curve beneath the Children’s Hospital Garage, Children’s Research Center, 333 Longwood Ave, and the Shapiro Center. A length of tangent track and a second 800-ft radius curve connects with a Brookline Avenue alignment. The alignment continues along Brookline Avenue and surfaces at the Yawkey Station/Air Rights Parcel 7 portal, as for Alternative 3A.


• The major issue with Alternative 3A-2 is in relation to building foundations and right-of-way. Passing beneath several buildings in the LMA is going to increase the chance of a conflict with foundations (details unknown at present) and increase potential for settlement-related problems.


Alternative 3A-3 shares same alignment as Alternative 3A from Leon Street/Ruggles Street, along Huntington Avenue, with an underground station on Huntington Avenue, and along Longwood Avenue until the intersection of Longwood Avenue and Binney Street. At this location, the 3A-3 alignment continues along Longwood Avenue before making a turn beneath the Emerald Necklace. A reverse curve brings the alignment into line with Brookline Avenue and surfaces at the Brookline Avenue/Air Rights Parcel 7 portal, as for Alternative 3A.

Extending the alignment along Longwood Avenue allows the Longwood Avenue station to be located at the intersection of Brookline Avenue. This provides increased spacing between this station and the station at Huntington Avenue.


• The Longwood Avenue station is located at the intersection of Brookline Ave rather than by Tugo Circle. This will likely increase disruption by constructing the station across the intersection but will eliminate potential complications of interfacing with the underground parking garage beneath the Harvard lawn.

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During further discussion of the Alternative 3-series alignments, it became clear that there were several significant advantages to locating the north-westerly tunnel portal between the Green Line “D” branch and the Landmark Center in the abandoned rail freight spur rather than in Yawkey Station/Air Rights Parcel 7:

• The abandoned rail freight spur/Landmark Center portal location affords adequate space for a TBM assembly chamber. Therefore, the TBM could be assembled at the northwest end of the tunnel and driven the full length of the tunnel alignment (horizontal radius permitting). This avoids the need for an intermediate cut and cover TBM assembly chamber at a location such as the Winsor School playing fields;

• The extensive length of cut and cover tunnel along Brookline Avenue and the associated traffic disruption would be avoided by eliminating the Brookline Avenue portal;

• The impacts and uncertainties regarding the interface with the Air Rights Parcel 7 development would be avoided; and

• Phase 3 routing option flexibility would be maximized (since the Brookline Avenue tunnel portal section would have major negative impacts on Phase 3 tunnel interface).

The need for two underground stations at either end of Longwood Avenue, in close proximity, was also questioned. Therefore the idea of providing a single underground station more centrally located along Longwood Avenue was explored as this could potentially provide a similar level of service but with reduced cost and reduced disruption during construction. The underground station at Huntington Avenue was therefore eliminated.

Finally, it was decided to further investigate the possibility of increasing the use of public right-of-way to minimize potential land takings and impacts on key institutions along the alignment.

Following further analysis and consultation with stakeholders, two further alignment variants emerged, referred to as Alternative H2(T) – “Tight Turn” and Alternative H2(T) – “Wide Turn”, presented in Attachment B. Additional sub-options were investigated including further variants in the alignment between Longwood Avenue and the Landmark Center portal.

4.3.1 Alternative H2(T) – “Tight Turn”

The objectives of Alternative H2(T) – “Tight Turn” are to:

• Maximize the use of public right-of-way;

• Reduce cost and disruption by providing only one underground station, centrally located along Longwood Avenue at Tugo Circle; and

• Minimize the length of abandoned tunnel structures for a potential Phase 3 conversion.

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Alternative H2(T) – “Tight Turn” is based on Alternative 3B and shares the same alignment from Leon Street/Ruggles Street, along Huntington Avenue and Longwood Avenue until the intersection of Longwood Avenue and Binney Street. At this location, the H2(T) alignment continues further along Longwood Avenue before making a tight turn (150-ft radius) from Longwood Avenue onto Brookline Avenue. The alignment continues along Brookline Avenue until a point just south of the Emerald Necklace, where a second tight turn (150-ft radius) would bring the alignment beneath the Emerald Necklace and the Muddy River to the abandoned rail freight spur/Landmark Center portal. The tight turns are approaching the absolute minimum horizontal radius for the BRT vehicles (100-ft) and may require a reduction in operating speed.

A single underground station would be provided in this alternative, centrally located along Longwood Avenue at Tugo Circle.

The tight turns could not be constructed using a TBM and would require use of other construction methods. The tight turns in this option would provide a connection point for a potential future Phase 3 alignment, however the choice of rail technology may be restricted depending on the final Phase 3 alignment.

The benefit of minimizing the length of abandoned tunnel in Phase 3 could only be realized if Phase 3 were to be light rail. This would require abandonment of the length of tunnel from the tight turn immediately south of the Emerald Necklace to the abandoned rail freight spur/Landmark Center portal. If heavy rail services were implemented in Phase 3, then the length of abandoned tunnel would extend to the tight turn at the intersection of Brookline Avenue and Longwood Avenue.

Construction of Alternative H2(T) – “Tight Turn” would be similar to Alternative 3B with the following main differences:

• Two underground structures will need to be built to enable the tight turns in the alignment to be made. These would most likely need to be built using cut and cover methods to allow sufficient space for the TBM to be turned and re-launched;

• The underground station at Huntington Avenue would be eliminated.

• Construction of the running tunnels using the SEM would eliminate the need for special structures at the tight turn locations.

4.3.2 Alternative H2(T) – “Wide Turn”

The objectives of Alternative H2(T) – “Wide Turn” are to:

• Minimize disruption to Brookline Avenue;

• Minimize surface disruption along the length of the tunnel alignment;

• Maximize the uninterrupted use of the TBM during the tunnel drive; and

• Reduce cost and disruption by providing only one underground station, centrally located along Longwood Avenue at Tugo Circle.

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Alternative H2(T) – “Wide Turn” is based on Alternative 3B and shares the same alignment from Leon Street/Ruggles Street, along Huntington Avenue and Longwood Avenue until the intersection of Longwood Avenue and Binney Street. At this location, the H2(T) – “Wide Turn” alignment would commence a wider horizontal curve to head beneath the Winsor School playing fields and the Emerald Necklace, before surfacing at the abandoned rail freight spur/Landmark Center portal. In this option, the TBM would pass beneath the Winsor School playing fields and the Emerald Necklace, but would create no surface disruption at these locations.

A single underground station would be provided in this alternative, centrally located along Longwood Avenue at Tugo Circle.

The structures required to perform the tight turns in H2(T) – “Tight Turn” are eliminated in this alternative and therefore the potential disruption to Brookline Avenue is also eliminated. In addition, the TBM drive would be in two discrete sections rather than four sections, simplifying the TBM drive and maximizing use of the TBM.

During development of this option the layout of the Leon Street portal was modified to include the protective works that would be required to the Stony Brook conduits. The portal structure was extended across Parker Street to the car park of the Sweeney Field. This results in the portal being tangent for the complete length and minimizes encroachment on Ruggles Street. The number of utility diversions required within Ruggles Street is potentially reduced by this configuration. It is proposed that this portal layout be adopted for any of the alternatives that include a portal in the vicinity of Leon Street.

Construction of Alternative H2(T) – “Wide Turn” would be similar to Alternative 3B with the following main differences:

• The turnout structure for Phase 3 would not be built during Phase 2, but an agreement would need to be reached between the Urban Ring Project and the Winsor School that any future development on the site would either incorporate the construction of the turnout, or would not prevent its construction at some date in the future;

• The underground station at Huntington Avenue would be eliminated.

4.3.3 Alternative H2(T) – Sub-options

Sub-options have also been evaluated for the busway tunnel section in the LMA to improve connectivity with the Green Line and to mitigate potential impacts to the Winsor School.

(i) Underground Stations on the Green Line

The possibility of constructing new underground stations on the Green Line “C” and “D” Branches to the west of Kenmore Station and in the vicinity of the Air Rights Parcel 7 development was considered to provide a more direct connection between the Urban Ring and the Green Line in this location. A summary of the key issues is presented below.

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• A single underground station capturing both Green Line “C” and “D” Branches, to the south of the Mass Turnpike, is not possible owing to the track configuration in this location. To the west of Kenmore Square the switch to branch the “C” and “D” lines starts approximately beneath the commuter rail line and the bifurcation is complete in the region of Maitland Street. A station could not be constructed along this length of track owing to the location of the switch. To have a station immediately south of the switch would require two separate stations on each branch of the Green Line.

• If a single station were to be constructed immediately to the north of the switch, then it would need to be located beneath the Mass Turnpike. The station platform length for a Green Line Station is 300-ft and this would place the northern end of the station platforms approximately 1000-ft from Kenmore Square station. The station would need to be mined beneath the Mass Turnpike. The station may interfere with the Beacon Street bridge piers and the Air Rights Parcel 7 development foundations.

• On the “D” Branch, there is a section of approximately 170-ft of straight track that would allow a two-car platform (74-ft long cars) to be constructed beneath 819 Beacon Street, as shown in Figure 4.15. A three-car platform would encroach on the 400-ft radius curves which may be acceptable to MBTA with a special waiver. The gradient through this area is approximately 0.3% which is within the limits specified for a station.

• On the “C” Branch, there is ample straight track to the south of the Mass Turnpike to locate a station, as shown in Figure 4.15. It would appear that the gradient in this area is less than 1.0% which is the maximum permissible for a Green Line station, although this requires confirmation. A three-car platform could easily be accommodated in this location.

• For a station in either location, construction would need to be carried out while keeping trains operational.

• Traffic would need to be maintained on Beacon Street during construction of the “C” Branch station.

• The Green Line stations would not provide an integrated interchange with the Urban Ring as there would be two additional underground stations for the Green Line and a separate surface station for the Urban Ring.

• There are operational considerations of adding a station to the Green Line and this may have an impact upon Green Line capacity and add to journey times.

Consideration of the above issues and the additional cost and complexity of construction in building two new underground stations on both branches of the Green Line without providing an integrated interchange with the Urban Ring resulted in these options not being pursued any further.

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Figure 4.15: Underground Stations on the Green Line

(ii) Alternative Locations and Configurations for the Landmark Center Portal

Three alternatives relating to the Landmark Center portal have been identified:

• Extend the Landmark Center portal further to the north and include an underground BRT station within the portal infrastructure;

• Revise the tunnel alignment to follow Park Drive with a split portal arrangement on Mountfort Street and an underground station beneath Park Drive to connect with the Green Line “C” and “D” Branches; and

• Revise the tunnel alignment to follow Park Drive with a portal located near the BU Bridge and underground stations beneath Park Drive and to the north of the Mass Turnpike.

These sub-options are described and discussed in a memorandum dated October 7, 2008 and included in Attachment C. The additional cost and the limitations imposed on Phase 3 rail conversion associated with the split portal option or the BU Bridge option have resulted in these alternatives not being considered any further. The improved connection with the Green Line and the increased ridership associated with the underground station at the Landmark Center portal is considered to be worth the additional cost and is therefore recommended for inclusion in the LPA.

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(iii) Longwood Avenue Alignment

In an effort to mitigate potential impacts to the Winsor School and increase the use of public ROW, further variants to the tunnel alignment for Alternative H2(T) were investigated. A preliminary evaluation indicates that extending the busway tunnel alignment to continue along Longwood Avenue prior to making the turn to the north to connect with the Landmark Center portal may afford an opportunity to alleviate the impact to the Winsor School and increase usage of public ROW. The location of the Phase 3 turnout structure and possible building foundation conflicts (375 Longwood Avenue) remain to be investigated. This alternative alignment is shown in Figure 4.16. The Alternative H2(T) – “Tight Turn” alignment also offers similar benefits in terms of alleviating impacts to the Winsor School and increasing usage of public ROW but places more restrictions on construction methodologies and on Phase 3 compatibility as discussed earlier in this report.

Figure 4.16: Longwood Avenue Alignment

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4.4 Tunneled Alignment Alternatives – Summary

A range of alignment alternatives have been developed for both the short tunnel and long tunnel options. These alignments have been further refined and developed on the basis of preliminary ridership and cost-benefit analyses, and in coordination with public consultation. The full range of alignment alternatives presented in this document are considered to be viable.

A summary table comparing the stations provided by each alternative, the approximate tunnel lengths and costs is given in Table 4.4.

The following sections present a general discussion on noise and vibration, electromagnetic fields, Phase 3 compatibility, and capital costs.

4.4.1 Noise and Vibration

Noise and vibration analyses have been undertaken by Harris Miller Miller & Hanson Inc. and address both construction phase and operations phase impacts for Urban Ring Phase 2. Some general issues related to Phase 3 impacts are also discussed. The noise and vibration analyses are detailed in a separate report and will be summarized in the RDEIR/DEIS document. A brief summary of the findings is presented below.

(i) Construction

The primary locations for assessing construction noise impact will be at the tunnel portals and the underground stations. Potential construction noise impacts and mitigations will be evaluated during engineering and design of the project, as more details of the construction scenarios are known.

Construction vibration levels were predicted for tunnel construction operations in the LMA. The LMA has a range of sensitive locations including residential locations and research facilities with vibration-sensitive equipment. Since many of the details regarding the specific equipment that is present and their locations at the research facilities is not known, potential vibration impact was assessed by determining the distance to impact for each criterion and each vibration source.

The vibration impact analysis indicates that vibration impact may occur for nighttime residential human use at distances up to 36 feet from the tunnel when tunneling in rock with efficient propagation conditions. For common vibration-sensitive equipment such as electron microscopes (classified as VC-A or VC-B equipment), ground-borne vibration impact may occur up to 57 feet from the tunnel depending on soil conditions. In consideration of the most highly-sensitive equipment (classified as VC-E equipment), ground-borne vibration impact may occur at distances up to 359 feet from the centerline of the tunnel.

As more detailed information regarding construction methodology, tunnel alignment, geotechnical conditions, specific equipment locations and building coupling losses becomes available during final design, more accurate assessments for each piece of equipment can be made and mitigations can be developed if required.

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(ii) Operations

The noise impact assessment indicates that there are no locations along the tunnel alignments, including stations, projected to have noise impacts during operation of the BRT service.

The vibration impact analysis indicates that the bus operations are not projected to generate vibration levels higher than existing vibration generated by current bus operations, trucks, and deliveries to buildings. In addition, because the primary source of vibration from rubber-tired vehicles is from roadway irregularities such as potholes, it is expected that buses operating on purpose-built, dedicated use busways or in the proposed tunnel would generate lower vibration levels than are currently experienced from buses and trucks on existing streets.

In Phase 3 of the project there is the potential for the tunnel to be converted to rail transit. While the noise and vibration impact assessment for that future phase of the project will be conducted separately from this Phase 2 analysis and does not have an effect on the analysis of Phase 2 impacts, the potential for rail transit vibration impacts through the LMA tunnel alternatives is addressed here. Unlike bus operations, there is significant potential for vibration impacts from rail transit through a tunnel in the LMA.

The extent of any potential impacts would need to be evaluated based on specific project factors, including vehicle type, speeds, and ground conditions in the LMA. However, a conservative estimate is that there is the potential for vibration impact on sensitive equipment at 400 feet or more without mitigation, depending on project-specific factors. There are a number of mitigation methods for rail transit available, including specially-designed fasteners and floating slab trackwork, which would have the potential to significantly reduce vibration levels through the LMA. Any Urban Ring Phase 2 tunnel recommendations would include a general assessment of vibration impacts (in accordance with Federal Transit Administration guidance) from Phase 3 rail operations. The general assessment would result in an upper bound for the potential for vibration impact from Phase 3 operations. This assessment would be based on available data in the literature, and assumptions regarding soil conditions and buildings foundations and Phase 3 rail operations. The assessment will include a discussion of the potential for reducing those impacts through a range of mitigation measures, at both the track and the receiver.

4.4.2 Electromagnetic Fields

An analysis of Electromagnetic Field (EMF)/Electromagnetic Interference (EMI) impacts has been undertaken by Gradient Corporation for Urban Ring Phase 2. Some general issues related to Phase 3 impacts have also been addressed. The EMF/EMI analysis is detailed in a separate report and will be summarized in the RDEIR/DEIS document. A brief summary of the findings is presented below.

Wherever electric propulsion is used, the key determinants of EMF/EMI potential are: magnitude of electric currents and voltages utilized by the vehicles, mass and size of the ferromagnetic material in the vehicle (for “moving metal” fields), proximity of sensitive receptors to the transit corridor, pattern of current and voltage time variations, spatial configuration of the conductors supplying electric power, the quantity of traffic, and the degree of EMF/EMI isolation required by sensitive receptors.

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The magnetic-field excursions from electric-propulsion currents are expected to have a frequency spectrum of 0 to 10 Hertz, and to occur at intervals (e.g., every two minutes) determined by the intermittency of bi-directional transit traffic. It is expected that the magnetic component of EMF/EMI produced by the transit system is likely to be the most problematic in terms of interference with sensitive research measurements. The highest magnetic fields are expected at grade, at the edge of the right of way (~15 feet from the route centerline). For the various technologies, this maximum is ~65 milli Gauss (mG) for hybrid electric/emission-controlled diesel/compressed natural gas BRT, ~210 mG for dual-mode BRT, ~1,010 mG for light rail technology, and ~1,610 mG for heavy rail technology. These values should be compared to the earth’s (steady) magnetic field, which is ~550 mG in Boston. However, these EMF/EMI fields drop rapidly with distance.

The analysis illustrates peak fields in the vicinity of the various alignment alternatives and also lists some potential mitigation measures that can be employed.

4.4.3 Phase 3 Compatibility

In assessing the conversion of Phase 2 tunnel alternatives to Phase 3, the rail alignment from Assembly Square to Dudley Square previously identified in the MIS and presented in the DEIR as Figure 2-1.3 is used as the base case for comparison. In addition, the analysis of Phase 3 compatibility also recognizes the potential for Phase 3 rail service connections to Allston, which was not included in the Urban Ring corridor in the MIS.

A summary matrix presenting Phase 3 compatibility is presented in Table 4.3. This shows three categories: basic compatibility (i.e. tunnel cross section and alignment criteria); basic features (i.e. portal elements, station elements, turnouts etc.); and advanced features (i.e. detailed elements of rail functionality). Also included is a section on non-compatible tunnel that would not be converted in Phase 3.

Major structural works required for Phase 3 that could be built during Phase 2 may include:

• Dedicated underground turnout structures to suit Phase 3 rail alignments;

• Longitudinal extension of underground stations to allow for Phase 3 platform lengths;

• Vertical extension of underground stations to allow Phase 3 station platforms to be built beneath the Phase 2 station (such that both BRT and rail could operate simultaneously); and

• Construction of a larger diameter tunnel to incorporate two decks - an upper deck for BRT, fitted out during Phase 2, and a lower deck provided during Phase 2 and fitted out for rail during Phase 3.

In general, where cut and cover structures are required for tight turns in Phase 2, these would be built to incorporate Phase 3 turnouts. In addition, where portals are required to be re-graded during Phase 3 conversion, the portals would be designed and constructed to accommodate these requirements in Phase 2.


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LRT HR LRT HR LRT HR LRT HR Description

Approximate

Abandoned Length

(feet)

Alternat ive 3 (Option 1 )LMA Tunnel (Ruggles - Yawkey)

� � � �

Note 1, Note 2 Note 1, Note 2 None None Yawkey (Parcel 7) Station would be abandoned 550

Mountfort Street Tunnel (BU Bridge) n/a n/a n/a n/an/a n/a n/a n/a

Mountfort street tunnel would not be used in Phase 3, but could

remain a BRT tunnel.0

Alternat ive 3 (Option 2 )LMA Tunnel (Ruggles - Yawkey)

� � � �


Mountfort Street Tunnel (Allston) n/a n/a n/a n/an/a n/a n/a n/a

Mountfort street tunnel would not be used in Phase 3, but could

remain a BRT tunnel.0

Alternat ive 3ALMA Tunnel (Ruggles - Yawkey)

� � � �


Alternat ive 3A-1LMA Tunnel (Ruggles - Yawkey)

� � �

-Note 1, Note 2 Heavy rail precluded by tight turns adjacent to the station at Brookline Avenue None None Yawkey (Parcel 7) Station would be abandoned 550


� � � �



� � � �


Alternat ive 3BLMA Tunnel (Ruggles - Park Drive)

� � � �

Note 1 Note 1 None NoneThe tunnel from the turnout to the Park Drive portal (including the

portal) would be abandoned2500

Alternat ive 3CLMA Tunnel (Ruggles - Allston)

� � � �

Note 1 Note 1 None NoneThe tunnel along Commonwealth Ave to Allston, including the

portals at Allston and BU Bridge, would be abandoned.8000

The platform tunnel for Yawkey/Kenmore station would be built and stub created for launch the

TBM toward Cambridge

The platform tunnel for Yawkey/Kenmore station would be built and stub created for launch the

TBM toward Cambridge

Alternat ive 4Ruggles to Cambridge

� � � �

Melnea Cass Blvd portal can be regraded to extend tunnel to Dudley Square. Melnea Cass Blvd portal can be regraded to extend tunnel to Dudley Square. Note 4 Note 4 The spur to Cambridge could be converted to HR 0

Cambridge portal would need to be regraded to extend the tunnel to Sullivan Square Cambridge portal would need to be regraded to extend the tunnel to Sullivan Square

Melnea Cass Blvd portal could be used for LRT to come to surface and run on surface route to

Dudley Square.

Allston Branch n/a n/a n/a n/an/a n/a n/a n/a

Conversion of the Allston branch is not part of the MIS identified

route, but could be achieved.0 or 7700 + 2 stations

Alternat ive 4ARuggles to Cambridge (& Kendall Sq)

� � �

Note 3Melnea Cass Blvd portal can be regraded to extend tunnel to Dudley Square. Melnea Cass Blvd portal can be regraded to extend tunnel to Dudley Square. None None The spur to Cambridge could only be used for LRT 0

Melnea Cass Blvd portal could be used for LRT to come to surface and run on surface route to

Dudley Square.Note 3

Vertical alignment through Park Drive would need to be deep to allow mined extension of station

tunnel beneath Green Line cut and cover box.

Vertical alignment through Park Drive would need to be deep to allow mined extension of station

tunnel beneath Green Line cut and cover box.

Allston Branch n/a n/a n/a n/an/a n/a n/a n/a

The spur to Allston would be abandoned (it could not be

converted to rail due to horizontal alignment radii)8200

Hybrid 2 (T ) - "T ight Turn"LMA Tunnel (Ruggles - Park Drive)

Note 1 Note 1If LR, tunnel abandoned from the Fenway tight turn up to and

inclduing the Park Drive portal.1500

A turnout structure immediately south of the Fenway allows Park Drive or Yawkey/Kenmore

alignments in Phase 3

A turnout structure at the intersection of Longwood/Brookline Aves allows Yawkey/Kenmore or

Cottage Farm alignments in Phase 3.

If HR, tunnel abandoned from the Longwood Ave tight turn up to

and including the Park Drive portal.3000

Hybrid 2 (T ) - "Wide Turn"LMA Tunnel (Ruggles - Park Drive)

Note 1 Note 1The tunnel from the turnout to the Park Drive portal (including the

portal) would be abandoned2500

All Alternat ivesn/a n/a n/a n/a

NOTES

1 Leon Street portal can be regraded to extend beneath Ruggles Station and extend to Dudley Square. The Phase 2 portal should be built with Phase 3 in mind to minimize future disruption and construction complexities.

2 Yawkey portal can be regraded to suit Yawkey/Kenmore Station and extension to Sullivan Square. The Phase 2 portal should be built with Phase 3 in mind to minimize future disruption and construction complexities.

3 The horizontal alignment is compatible with LRT but not Heavy Rail. The alignment to Cambridge could potentially be amended to be Heavy Rail compatible once further information is available on foundation constraints.

4 Hawes St station (Green Line "C" Branch) would be extended to meet the turnout, thereby creating the full station box for Phase 3.

5 Special tunnel lining rings would used where future station extension walls to be built.

6 Advanced items that could be considered during detailed design include: accommodation of rail systems within the tunnel (utility ducting, supports etc), stray current protection, roadway construction details that facilitate later removal and replacement with rail, platform dimensions for LRT conversion.

7 Consider the diversion of existing utilities (e.g. sewers, water mains, etc) during Phase 2 that will accommodate the works associated with Phase 3 to minimize cost, disruption, and schedule.

Non-compatible tunnel

A turnout would be included during Phase 2 (beneath the Winsor School playing fields) to allow a Pilgrim Road tunnel alignment compatible with Phase 3 LR/HR to Park Drive or

Passive provision for future construction of a turnout beneath the Winsor School allows either LR or HR to Park Drive or Yawkey/Kenmore.

Note 6

Note 7

Note 5

Phase 3 Features (basic)Phase 3 Features

(advanced)Phase 3 Compatible (basic)

Tunnel Cross Section Alignment

Where portals are to be regraded, the portal should be designed and constructed during Phase 2 to accommodate the regrade during Phase 3.

Passive provision is made in the alignment for the extension of stations (tangent, level track).

Table 4.3: Phase 3 Compatibility Matrix


4.4.4 Preliminary Capital Cost Estimate of Options

A preliminary capital cost estimate for each of the tunneled options has been prepared by Keville Enterprises Inc., and is presented in Table 4.4. The estimate provides a comparison between each of the tunnel alternatives, but does not indicate the change in cost for the remainder of the Urban Ring (e.g. change to surface routing options required to connect to the tunnels).

Rug

gles

Hun

tingt

on A

ve(G

reen

Lin

e "E

" Bra

nch)

Long

woo

d Av

enue

(Ave

Lou

is P

aste

ur)

Long

woo

d Av

enue

(Bro

oklin

e Av

e)

Yaw

key

(Par

cel 7

)

Yaw

key/

Kenm

ore

Long

woo

d(G

reen

Lin

e "D

" Bra

nch)

Haw

es S

treet

(Gre

en L

ine

"C" B

ranc

h)

Park

Driv

e (G

reen

Lin

e "B

" &

"C" B

ranc

hes)

Bost

on U

nive

rsity

Wes

t(G

reen

Lin

e “B

” Bra

nch)

Bost

on U

nive

rsity

Cen

tral

(sou

th o

f BU

Brid

ge)

Bost

on U

nive

rsity

Cen

tral

(Gre

en L

ine

“B” B

ranc

h)

Wes

t Sta

tion

TOTA

L N

UM

BER

OF

UN

DE

RG

RO

UN

D

STAT

ION

S Total Length of Tunnel *

(feet)Total Estimated

Cost

Alternative 3 (Option 1) 3 12,500 2.8 billion$

LMA Tunnel (Ruggles - Yawkey) 3 9,800Mountfort Street Tunnel (BU Bridge) 0 2,700

Alternative 3 (Option 2) 3 17,100 3.6 billion$

LMA Tunnel (Ruggles - Yawkey) 3 9,800Mountfort Street Tunnel (Allston) 0 7,300

Alternative 3A 3 9,800 2.2 billion$ LMA Tunnel (Ruggles - Yawkey) 3 9,800

Alternative 3B 2 7,900 1.7 billion$ LMA Tunnel (Ruggles - Park Drive) 2 7,900

Alternative 3C 4 17,700 3.5 billion$ LMA Tunnel (Ruggles - Allston) 4 17,700

Alternative 4 8 23,300 5.2 billion$

Ruggles to Cambridge 6 15,500Allston Branch 2 7,800

Alternative 4A 7 30,500 6.3 billion$ Ruggles to Cambridge (& Kendall Sq) 5 22,200Allston Branch 2 8,300

Alternative 3A-1 3 9,800 2.2 billion$

LMA Tunnel (Ruggles - Yawkey) 3 9,800

Alternative 3A-2 3 9,100 2.1 billion$ LMA Tunnel (Ruggles - Yawkey) 3 9,100

Alternative 3A-3 3 11,000 2.4 billion$ LMA Tunnel (Ruggles - Yawkey) 3 11,000

Hybrid 2(T) - "Tight Turn" 1 8,000 1.5 billion$ LMA Tunnel (Ruggles - Park Drive) 1 8,000

Hybrid 2(T) - "Wide Turn" 1 7,900 1.5 billion$ LMA Tunnel (Ruggles - Park Drive) 1 7,900

* length of tunnel is approximate and includes portal structures and underground stations

Note 1 – Columns in the above table refer to the underground stations associated with each alternative.Note 2 – Total costs are preliminary in 2007 dollars including contingency and soft costs.

Stag

e 1

Stag

e 2

Stag

e 3

Table 4.4: Preliminary Estimate of Capital Cost for Tunnel Alternatives

The costs Presented here are for comparison purposes only. Further cost estimates have been prepared in more detail for the LPA and reflect a more detailed level of engineering analysis. These cost estimates are presented in the RDEIR/DEIS.

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The station costs in Table 4.4 are for Urban Ring Phase 2 BRT stations only. If the stations were to be built to accommodate Phase 3 rail transit during construction of Phase 2, then each station cost for each alternative would need to increase by approximately $22 million for light rail or $51 million for heavy rail. Additional construction of underground works that would enable connection of a future Phase 3 tunnel into the proposed Phase 2 tunnel would add between $20 to $96 million, depending on the alternative and the final configuration of the Phase 3 alignment.

The number of rail-ready facilities (e.g. embedded rail, stray current protection, utilities, etc.) that are provided within the bus tunnel has not be established. These items, if included, will add cost during Phase 2 for a potential future rail conversion.


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5 Current Locally Preferred Alternative for Busway Tunnel

The current Locally Preferred Alternative (LPA) for the busway tunnel is based on the Alternative H2(T)

alignment options. The following features from the Alternative H2(T) alignment options form part of the

LPA busway tunnel:

• The east portal location and configuration at Leon Street within the MBTA ROW;

• The alignment of the tunnel from the east portal at Leon Street to the proposed underground station beneath Longwood Avenue (following the alignment of Huntington Avenue);

• The location of the proposed underground station beneath Longwood Avenue in the vicinity of Avenue Louis Pasteur;

• The location of the west portal adjacent to the Landmark Center and the Green Line “D” Branch within the abandoned CSX ROW; and

• The inclusion of an underground BRT station as part of the west portal structure adjacent to the Green Line “D” Branch to provide better connectivity with existing Green Line stations.

There are currently three different options for the section of busway tunnel alignment between Longwood

Avenue and the west portal, presented earlier in this report as Alternative H2(T) – “Tight Turn”,

Alternative H2(T) – “Wide Turn”, and the Longwood Avenue Alignment, herein these options are

referred to as eastern, central and western, respectively.

A summary of the lengths of running tunnel for each alignment alternative and the length of tunnel that

would need to be abandoned on conversion to Phase 3 rail transit is presented in Table 5.1. The LPA

busway tunnel including the western, central, and eastern alignment options is presented in Figure 5.1.

Length of Running Tunnel (feet) Alignment

Alternative

Constructed in Phase 2 Abandoned on Conversion

to Phase 3 Rail

Minimum Horizontal

Radius of Running Tunnel

(feet)

Western 6,293 2,710 700

Central 5,710 1,630 700

Eastern 5,895 765 (light rail)

2,545 (heavy rail)

150

Table 5.1: Summary of LPA Tunnel Lengths


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Figure 5.1: LPA Busway Tunnel

Advantages and disadvantages of the three alignment alternatives are summarized below.

Western Alignment

Advantages:

• Maintains full flexibility in Phase 3 alignments;

• Increases use of Public ROW and minimizes impacts to private properties;

• Avoids interface with Shapiro Center building foundations at the corner of Longwood Avenue and Brookline Avenue; and

• The minimum radius horizontal curve is 700-ft allowing flexibility in the choice of construction method, ensuring compatibility with Phase 3 heavy rail, and potentially eliminating speed restrictions for BRT operation.

Disadvantages:

• The Phase 3 turnout structure will impact utilities and disrupt traffic as it will be located in the street;

• Potential foundation conflict with 375 Longwood Avenue for construction of Phase 3;

• Increased length of tunnel to be constructed during Phase 2; and

Central Alignment

Western Alignment

Eastern Alignment


• Increased length of abandoned tunnel on conversion to Phase 3.

Central Alignment

Advantages:

• Maintains full flexibility in Phase 3 alignments with minimized length of tunnel constructed during Phase 2 and minimized length of tunnel abandoned during Phase 3 conversion;

• The turnout is not located within the street therefore minimizing disruption to traffic and reducing potential for utility diversions; and

• The minimum radius horizontal curve is 700-ft allowing flexibility in the choice of construction method, ensuring compatibility with Phase 3 heavy rail, and potentially eliminating speed restrictions for BRT operation.

Disadvantages:

• Passes directly beneath the Winsor School and will require close coordination with any development proposals that the Winsor School may propose; and

• Interfaces with Shapiro Center building foundations at intersection of Longwood Avenue and Brookline Avenue.

Eastern Alignment

Advantages:

• Increases use of Public ROW and minimizes impacts to private properties; and

• Minimizes length of abandoned tunnel on conversion to Phase 3 heavy rail, but only if Phase 3 is to be light rail.

Disadvantages:

• The minimum radius horizontal curve is 150-ft, placing more restrictions on the choice of construction methods, potentially reducing flexibility in terms of Phase 3 conversion, and potentially requiring speed restrictions to allow safe operation of the BRT service;

• Interface with Muddy River Restoration project structures;

• Interface with Shapiro Center building foundations at intersection of Longwood Avenue and Brookline Avenue;

• Construction of a turnout structure at the intersection of Brookline Avenue and the Fenway will be challenging regardless of the construction method employed. Cut and cover methods will cause major surface disruption in close proximity, and possibly within, the environmentally sensitive Fenway and Emerald Necklace. Use of the SEM would require major ground improvement given the size and geometry of the structure. Such ground improvement methods would almost certainly require surface disruption; and

• Shallow ground cover to the Muddy River at the portal approach may require additional ground improvement.

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Preliminary plan and profile drawings of the LPA busway tunnel are presented in Attachment D. The final selection of an alignment (western, central, or eastern) for the LPA busway tunnel will depend on more detailed geotechnical information and site investigations, assessment of construction methodologies, costs, environmental impacts and more detailed engineering analyses that will be undertaken during preliminary engineering.

Estimates of the number of trucks required to deliver and remove bulk materials to and from site during construction of the LPA busway tunnel are presented as histograms in Attachment D, with the option to use rail during construction at the Landmark Center portal resulting in an additional set of histograms. The histograms are intended to provide an order of magnitude estimate commensurate with the current stage of the planning process, and are therefore calculated relative to the central alignment only. These estimates will need to be refined once the alignment is fully defined and preliminary engineering studies have been progressed. The use of rail transport and the identification of potential truck haul routes will require further study and coordination with the relevant authorities and agencies during subsequent stages of the planning process.


6 Conclusions and Recommendations for Further Work

A broad range of busway tunnel alignment alternatives have been developed. Consultation with key stakeholders, in combination with assessment of key issues including: costs; ridership; and environmental impacts, has resulted in additional development of more promising alignment alternatives and ultimately, a recommendation for a LPA for the busway tunnel. The LPA for the busway tunnel still includes some flexibility in terms of the alignment of the tunnel, but provides a well defined extent of the tunnel, location of tunnel portal structures and location of underground stations. The following list provides a basis for further work on the busway tunnel:

• Continue to pursue relevant organizations for existing geotechnical data;

• Continue to pursue relevant organizations for foundation information;

• Conduct project specific geotechnical investigations;

• Gather additional information on major and strategic public and private utilities along the corridor and develop utility relocation plans;

• Once further geotechnical and utility information is available, perform a detailed evaluation of construction methodologies for the entire length of the LPA busway tunnel with respect to:

- Costs;

- Environmental impacts;

- Geotechnical conditions;

- Noise and vibration;

- Schedule;

- Settlements;

- Structure function;

- Surface disruption; and

- Utilities.

• Perform detailed site survey of critical locations (e.g. corridor between Landmark Center and Green Line “D” Branch) to confirm site geometry and clearances;

• Advance engineering study of portal adjacent to Landmark Center to confirm impacts on abutters and extent of protective measures required (e.g. Landmark Center, Green Line infrastructure, Park Drive bridge, 440 Park Drive, etc);

• Assess impacts on Green Line operations and measures required to ensure continuing operation during construction in coordination with MBTA;

• Perform preliminary settlement and building response assessments for preferred route options and refine construction methodology as required;

• Obtain latest guidance from MBTA to confirm assumptions regarding Phase 3 rail criteria (e.g. platform lengths etc);

• Obtain information from MBTA on the Silver Line Phase 2 project (constructed) and the proposed Silver Line Phase 3 project (in planning);

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• Perform more detailed and site-specific station planning to verify the accommodation and layout of mechanical and electrical equipment rooms, access, egress, etc.;

• Re-assess the BRT vehicle envelope requirements and examine the possibility of reducing the tunnel size;

• Assess output from noise and vibration studies to determine whether mitigation is required or if alternative alignments should be investigated;

• Finalize ridership projections and calculate cost-effectiveness measures for all alternatives.


Attachment A Typical Station Layout

A-1 232551/01/G - November, 2008/A-1 of 1


B-1 232551/01/G - November, 2008/B-1 of 4

Attachment B Tunneled Alignment Alternatives


B-2 232551/01/G - November, 2008/B-2 of 4

B.1 Alternatives Development Stage 1

Alternatives: 3, 3A, 3B, 3C, 4, and 4A

Cambridge

Somervi l le

Medford Everett

Chel sea

EastBoston

South Boston

Dorchester

Roxbury

Brookline

Proposed AlignmentMixed TrafficBuslaneBusway (Surface)Busway (Tunnel)Proposed StopTunnel Portal

Urba n R ing Pha se 2 RDEI R/ DEI SUrba n R ing Pha se 2 RDEI R/ DEI S

Alternative 3May 14, 2007

Cambridge

Somervi l le

Medford Everett

Chel sea

EastBoston

South Boston

Dorchester

Roxbury

Brookline



Alternative 3AMay 14, 2007

Cambridge

Somervi l le

Medford Everett

Chel sea

EastBoston

South Boston

Dorchester

Roxbury

Brookline



Alternative 3BMay 14, 2007

Cambridge

Somervi l le

Medford Everett

Chel sea

EastBoston

South Boston

Dorchester

Roxbury

Brookline



Alternative 3CMay 14, 2007

Cambridge

Somervi l le

Medford Everett

Chel sea

EastBoston

South Boston

Dorchester

Roxbury

Brookline



Alternative 4May 14, 2007

Cambridge

Somervi l le

Medford Everett

Chel sea

EastBoston

South Boston

Dorchester

Roxbury

Brookline



Alternative 4AMay 14, 2007


B-3 232551/01/G - November, 2008/B-3 of 4


Alternatives: 3A-1, 3A-2, 3A-3

FENWAY

PARK DR

HUNT

ING

TON

AVE

BEACON ST

BR

OO

KLI

NE

AV

E

LONGWOOD AVE

RIV

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R S

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BOYLSTO

N ST

WARD ST

TREM

ON

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RUGGLES ST

FORSYTH ST

SAINT M

ARYS ST

MOUNTFORT ST

LEON

ST

PALA

CE

RD

HE

ME

NW

AY ST

PETERBOROUGH S

T

CARLTON ST

QUEENSBERRY ST

JERSEY ST

CH

AP

EL

ST

KILMARNOCK ST

VAN N

ESS ST

PIL

GR

IM R

D

FIELD ST

COLCHESTE

R ST

HAWES ST

GAINSBOROUGH ST

IVY ST

MONMOUTH

ST

BEECH RD

BUSWELL

ST

MASSACHUSETTS TURNPIKE AGASSIZ RD

PRENTISS ST

MCGREEVEY WAY

AVE

LOU

IS PA

STE

UR

YAWKEY WAY

KENT ST

MUSEUM RD

TAVE

RN

RD

SPEA

R PL

WHITTIER ST

LOUIS PRANG ST

CHATHAM

ST

EVA

NS

WAY

BIN

NE

Y S

T

AN

NU

NC

IATI

ON

RD

TETLOW ST

GREENLEAF ST

SAIN

T ST

EPHE

N ST

BABBITT ST

FORSYTH WAY

HAWES P

L

VAN

CO

UV

ER

ST

MEDFIELD

ST

EUSTON ST

UNNAMED RD

HA

LLE

CK

ST

MIN

DO

RO

ST

SAIN

T B

OTO

LPH

ST

BURLINGTON AVE

COMMONWEALTH AVE

OVERLAND ST

ABERDEEN ST

ARUNDEL ST

SHORT ST

BILLS

CT

FULLERTON ST

KESWICK STFENCT ST

MONMOUTH CT

OPERA PL

AU

TUM

N S

T

PUBLIC

ALLEY 807

CO

LUM

BUS

AVE

PUBLIC ALLEY 810

MINER ST

IPSWICH ST

SA

INT A

LPH

ON

SU

S S

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MUNSON ST

EDGAR ST

PU

BLI

C A

LLE

Y 1

001

SYMPHONY RDCU

MM

ING

TON

ST

BLA

CK

FAN

CIR

CLE

MAITLAND ST

BORLAND ST

PU

BLIC

ALLE

Y 811

FENWAY CONNECTOR TO PARK DR

SAINT

MARYS CT

PUBLIC ALLEY 822

HEMENWAY TER

EVA

NS

WAY

UNNAMED RD

HUNT

ING

TON

AVE

COMMONWEALTH AVE

MASSACHUSETTS TURNPIKE

VAN

CO

UV

ER

ST

TREM

ON

T ST

PIL

GR

IM R

D

FORSYTH WAY

BEACON ST

UNNAMED RD

Urban R ing P hase 2 RDE IR/DE IS

0 450225

Feet Tunnel AlternativesData supplied by MassGIS and LMA. June 27, 2007

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1:5,400 Fenway - LMADRAFT

Common to All 3A-2

3A-3

3A3A-1

3A & 3A-1

RugglesStation

Yawkey/KenmoreStation

Muddy

Rive

r

BackBayFens

Tunnel AlignmentSurface AlignmentProposed StationExisting MBTA Stops

3B

Brookline Ave. Station Tugo Station

Huntington Ave.Station

B O S T O N

B R O O K L I N E


B-4 232551/01/G - November, 2008/B-4 of 4


Alternatives: H2(T) – “Tight Turn” and H2(T) – “Wide Turn”

FENWAY

PARK DR

HUNT

ING

TON

AVE

BEACON ST

BR

OO

KLI

NE

AV

E

LONGWOOD AVE

RIV

ERW

AY

PAR

KE

R S

T

BOYLSTO

N ST

WARD ST

TREM

ON

T ST

RUGGLES ST

FORSYTH ST

SAINT M

ARYS ST

MOUNTFORT ST

LEON

ST

PALA

CE

RD

HE

ME

NW

AY ST

PETERBOROUGH S

T

CARLTON ST

QUEENSBERRY ST

JERSEY ST

CH

AP

EL

ST

KILMARNOCK ST

VAN N

ESS ST

PIL

GR

IM R

D

FIELD ST

COLCHESTE

R ST

HAWES ST

GAINSBOROUGH ST

IVY ST

MONMOUTH

ST

BEECH RD

BUSWELL

ST

MASSACHUSETTS TURNPIKE AGASSIZ RD

PRENTISS ST

MCGREEVEY WAY

AVE

LOU

IS PA

STE

UR

YAWKEY WAY

KENT ST

MUSEUM RD

TAVE

RN

RD

SPEA

R PL

WHITTIER ST

LOUIS PRANG ST

CHATHAM

ST

EVA

NS

WAY

BIN

NE

Y S

T

AN

NU

NC

IATI

ON

RD

TETLOW ST

GREENLEAF ST

SAIN

T ST

EPHE

N ST

BABBITT ST

FORSYTH WAY

HAWES P

L

VAN

CO

UV

ER

ST

MEDFIELD

ST

EUSTON ST

UNNAMED RD

HA

LLE

CK

ST

MIN

DO

RO

ST

SAIN

T B

OTO

LPH

ST

BURLINGTON AVE

COMMONWEALTH AVE

OVERLAND ST

ABERDEEN ST

ARUNDEL ST

SHORT ST

BILLS

CT

FULLERTON ST

KESWICK STFENCT ST

MONMOUTH CT

OPERA PL

AU

TUM

N S

T

PUBLIC

ALLEY 807

CO

LUM

BUS

AVE

PUBLIC ALLEY 810

MINER ST

IPSWICH ST

SA

INT A

LPH

ON

SU

S S

T

MUNSON ST

EDGAR ST

PU

BLI

C A

LLE

Y 1

001

SYMPHONY RDCU

MM

ING

TON

ST

BLA

CK

FAN

CIR

CLE

MAITLAND ST

BORLAND ST

PU

BLIC

ALLE

Y 811

FENWAY CONNECTOR TO PARK DR

SAINT

MARYS CT

PUBLIC ALLEY 822

HEMENWAY TER

EVA

NS

WAY

UNNAMED RD

HUNT

ING

TON

AVE

COMMONWEALTH AVE

MASSACHUSETTS TURNPIKE

VAN

CO

UV

ER

ST

TREM

ON

T ST

PIL

GR

IM R

D

FORSYTH WAY

BEACON ST

UNNAMED RD

Urban R ing P hase 2 RDE IR/DE IS

0 450225

Feet

October 4, 2007 Hybrid 2(T) TunnelAlignment Developed byHatch, Mott, MacDonald

Data supplied by MassGIS and LMA. November 6, 2007

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-- 5

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51 P

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1:5,400Fenway - LMADRAFT

Hybrid 2(T) TunnelAlignment

Phase 3via Kenmore

RugglesStation

Yawkey/KenmoreStation

Muddy

Rive

r

BackBayFens

Proposed Station

Existing MBTA Stops

Hybrid 2(T) Tunnel Alignment October 4, 2007Phase 3 Potential Alignments

Tugo Station

B O S T O N

B R O O K L I N E

Phase 3via Park Dr.

Hybrid 2(T) Tight TurnTunnel Alignment

Hybrid 2(T) Wide TurnTunnel Alignment

Potential FutureTurnout for Phase 3

Potential FutureTurnout for Phase 3


C-1 232551/01/G - November, 2008/C-1 of 1

Attachment C Alternative H2(T) Sub-options Memorandum

M E M O

Date: October 7, 2008

To: Ned Codd, P.E. Project Manager, EOTPW

From: James A. Doyle, AICP, Project Manager Earth Tech AECOM CC: Jeff Maxtutis, AICP David Watson, HMM File

Subject: Urban Ring Phase 2 RDEIR/DEIS Review and Comparison of LPA Tunnel Options

Introduction

The Urban Ring Phase 2 RDEIR/DEIS planning process developed a Locally Preferred Alternative (LPA) established in early 2008. The planning process has recommended a tunnel segment as part of the LPA, and that tunnel is included in the current review draft of the environmental document. The current LPA tunnel comprises a busway tunnel approximately 1.5 miles in length extending from a portal on the east adjacent to Ruggles Station and a portal on the west adjacent to the Landmark Center, with one underground station in the Longwood Medical Area. Connections with the Green Line occur at Kenmore Square where the Green Line B, C, and D Lines can be reached at a single station directly served by at least one of the three Urban Ring BRT routes planned in this area. The Landmark Portal Option has the BRT7 route serving Kenmore Square directly, while the other two routes (BRT5 and BRT6) would rely on walk connection from Yawkey to reach Kenmore Square. All three routes serve Yawkey station directly. Most CAC members, stakeholders, and members of the public have been generally supportive of the proposed LPA tunnel, though some parties have raised concerns about its connections with the Green Line via Yawkey and Kenmore Square due to walk distances, routing complexity, and congestion in the Kenmore Square roadway network and bus terminal. In response to these concerns, the project team has explored a number of options for modifying or extending the west end of the LPA tunnel and moving or adding stations to improve Green Line connectivity and overall service. This memorandum reviews the engineering feasibility for different tunnel options, and evaluates three new options relative to key measures of engineering feasibility, Green Line connectivity, commuter rail connectivity, ridership, cost, and compatibility with Phase 3. Summary Descriptions

The following is a summary of the three new tunnel options that have been evaluated in detail. These are the “Landmark Portal with Fenway Station Option,” the “Mountfort Street Split Portal Option,” and “BU Bridge Portal Option,” each of which has different portal and station characteristics at its northwestern end.

Memo – October 7, 2008 Page 2 Evaluation of Tunnel Options

The Landmark Portal with Fenway Station Option is a modified version of the current LPA that would retain the same tunnel alignment as the LPA and would provide an underground additional station. The new underground station would be located near the western portal, at the Landmark Center adjacent to the Green Line D Fenway Station. This would require extending the portal slightly northward beneath Miner Street. In this option service at Yawkey would be the same as in the current LPA with all three routes serving Yawkey station directly for connection with commuter rail. Direct connection with the Green Line D Branch would occur at the Fenway Station, and connection with the Green Line C Branch would be via walk connection to St. Mary’s Station. Green Line B Branch connection would be at the BU Central Station on Commonwealth Avenue as in the current LPA. The BRT7 in this option would terminate at Yawkey rather than at Kenmore Square. The Mountfort Street Split Portal Option would realign the tunnel beneath Park Drive and extend it to the Mountfort Street corridor. This option would have one additional underground station, which would be located beneath Park Drive, roughly between Beacon Street and the Green Line D Branch. This station would have headhouse access from the C Branch at Beacon Street (near St. Mary’s Station) and the D Branch at Fenway Station. It would surface in Mountfort Street in a split portal configuration, with a westbound portal surfacing just west of St. Mary’s Street and the eastbound portal surfacing just west of Carlton Street. The BU Bridge Portal Option would significantly extend the tunnel alignment and would add two new underground stations. It would extend the tunnel beneath Park Drive and the Massachusetts Turnpike, and portal near the BU Bridge. One new underground station would be located beneath Park Drive between the Fenway D Branch station and Beacon Street (a short walk to the St. Mary’s C Branch station); the other new underground station would be beneath Commonwealth Avenue near the BU Central B Branch Station. This option would bypass Kenmore Station (providing a more direct alignment); it would also bypass Yawkey Station (eliminating the direct connection to the Framingham/Worcester commuter rail, which would become a walk connection from the new underground Park Drive Station).

Engineering Feasibility

Over the course of the RDEIR/DEIS planning process, the project team has reviewed a wide range of different tunnel alignments, station locations, and portal configurations, including six of the nine Build Alternatives. A key element of the tunnel alternatives evaluation has been a review of engineering feasibility, from the perspective of constructability as well as basic physical configuration. The following is a summary of the engineering feasibility of the three options under study.

Landmark Portal with Fenway Station Option

This option would modify the LPA by extending the proposed portal structure at the Landmark Center to include a shallow underground BRT station parallel to the Green Line “D” Branch. The portal structure would be extended to meet with the re-alignment of Maitland Street proposed by Meredith Management as part of the Parcel 7 Air Rights development proposals. This option is shown in Figure 1. The following are principal issues with this option:

• The available corridor width adjacent to the Landmark Center is relatively narrow, constrained by the Landmark Center to the south and the Green Line “D” Branch incline to the north. Construction of a station in this area would require the station walls to be located very close to both abutting structures. As a result, additional ground treatment and support measures may be required to enable construction.


• This option would entail construction impacts, ventilation structures, and station access at the D Branch Fenway Station.

• The relatively narrow corridor between the Landmark Center and the Green Line “D” Branch requires that the station platforms be staggered through this area to minimize the width of the station structure.

• A pump house associated with the Green Line portal in the vicinity of Miner Street would need to be relocated. This may have temporary impacts on the parking lot at this site.

• The gradient through the portal structure will be less than the maximum allowable gradient and would tie in with the surface grading plans proposed by Meredith Management as part of the Parcel 7 Air Rights development.

• The BRT route in this option would avoid the need to cross Miner Street at grade. The portal structure would prevent future surface roadway connection between existing Munson Street and Burlington Street.

Recommendation: With appropriate planning and construction staging, the engineering and construction

issues of this option could be managed. Retain for further analysis and comparison to LPA.

Mountfort Street Split Portal

This option is based on a proposals submitted to EOT by Harvard University. This option would require a realignment of the LPA tunnel to align with Pilgrim Road. The tunnel would follow the alignment of Pilgrim Road, making a turn to the west to pass beneath Park Drive and the Green Line D and C Branches. An underground BRT station would be constructed beneath Park Drive between the C Branch at Beacon Street and the Green Line D Branch with headhouses located to the north end (south side of Audubon Circle) and south end (immediately south of Fenway Station). The tunnel alignment would then continue north beneath Park Drive, making a turn to the west beneath Mountfort Street where a split portal arrangement would bring the northbound and southbound tunnel lanes up to existing grade in separate structures. This option is shown in Figure 2. The routing of the BRT service would be modified from the LPA to include the additional length of tunnel and underground station. In addition, further surface routing modifications would be required to incorporate northbound BRT service over Carlton Street with a surface station over the Mass Turnpike, and southbound BRT service along Mountfort Street with a surface station to the south of Commonwealth Avenue. Construction of the portal structures and connecting tunnels would take place within Mountfort Street. The crossing beneath St Mary's Street would be relatively shallow as the alignment is just inside the portal at this location. This may conflict with the foundations of the St Mary's Street bridge, requiring protective works to the bridge or possibly re-construction. Construction work would also need to accommodate the topography to the north of Mountfort Street, including a steep drop to the Commuter Rail line, and maintenance and protection of traffic along Mountfort Street, Carlton Street, and St Mary’s Street. If an additional station were to be constructed on the “C” Branch to allow a direct vertical connection with the Urban Ring, the construction would likely cause major disruption to Audubon Circle. In any case, Proximity of the proposed tunnel portals in this option to the existing Commuter Rail line may offer opportunities for the removal of excavated material and supply of materials during construction. However, the narrow, constrained alignment of Mountfort Street and the adjacent historic residential neighborhood of Cottage Farm would pose challenges to a tunnel servicing operation.


The following are principal issues with this option:

• The southbound portal would be inaccessible from the future southbound BRT route that uses the BU Academy and University Road alignment; this would necessitate Urban Ring use of the BU Bridge for crossing the Charles River, or the so-called “slip ramp” option to connect from the Grand Junction Railroad up to Commonwealth Avenue west of the BU Bridge.

• The proposed portal structures would occupy a significant portion of Mountfort Street’s width. Mountfort Street currently accommodates four narrow lanes in approximately 40-45 feet; each of the two proposed portal structures would occupy at least 20 feet, which would reduce Mountfort Street to 20-25 feet. This means that if Mountfort Street were to remain in its current alignment, it would be reduced to one lane in each direction between St. Mary’s Street and Essex Street. Furthermore, these lanes would be offset from each other by approximately 20 feet in the vicinity of Carlton Street (due to the fact that the eastbound portal is along the south side of the street and the westbound portal is along the north side of the street). This would either result in significant roadway design and traffic operations impacts or else it would require a major reconstruction and widening of Mountfort Street.

• Construction of the Urban Ring tunnel in this option between the Green Line C Branch tunnel and the D Branch would likely require additional ground treatment and protective works.

• This option would entail construction impacts, ventilation structures, and station access at Audubon Circle, as well as at the D Branch Fenway Station.

• The proximity of the proposed tunnel portals in this option to the existing Commuter Rail line may offer opportunities for the removal of excavated material and supply of materials during construction. However, the narrow, constrained alignment of Mountfort Street and the adjacent historic residential neighborhood of Cottage Farm would pose challenges to locating and operating construction laydown and removal of tunnel excavate.

• The portal structures are inconsistent with any future re-alignment of Mountfort Street, such as the one proposed by Boston University.

• The portal structures would have permanent impacts and construction phase impacts on the historic Cottage Farm neighborhood.

• The proposed tunnel alignment would eliminate the direct BRT connection with the Framingham/ Worcester commuter rail line at Yawkey Station.

• The station platform shown on Mountfort Street is very close to the intersection and is also on a curve. The location of this station platform is limited by the gradient required to enter the tunnel.

• This option reduces the utility of tunnel alignments for Urban Ring Phase 3. A large portion of the tunnel would be inconsistent with a Phase 3 alignment through Kenmore Square because it passes beneath Park Drive toward the BU Bridge/Allston. In addition, a large portion of the tunnel would be inconsistent with a Phase 3 alignment toward the BU Bridge/Allston because it ascends to portal in Mountfort Street, while a Phase 3 tunnel would need to descend to pass beneath the Mass Turnpike.

In summary, the engineering, construction, and compatibility issues with municipal and institutional plans seriously impact the feasibility of this option. For this reason, this option should not be pursued in its current configuration. Instead, this option was modified to achieve the objectives of the proposal in a feasible configuration that would extend the tunnel to the BU Bridge; this is described below as the BU Bridge Portal Option. Recommendation: Design challenges, construction issues, traffic impacts, and abutter impacts of this

option are very high. Do not pursue, reconfigure to pass beneath the Mass Turnpike and portal at the BU

Bridge.


BU Bridge Portal Option

This option is a reconfiguration of the Mountfort Street Split Portal Option. Instead of the tunnel surfacing along Mountfort Street, it would stay at depth, pass beneath the Mass Turnpike and head toward the BU Bridge where the alignment would connect with the Grand Junction Railroad (GJRR) through a portal structure emerging from beneath the Boston University Bridge approach road. Two underground stations would be provided, one beneath Park Drive (as in the option to extend the tunnel to Mountfort Street) and one adjacent and to the north of the Mass Turnpike between St Mary’s Street and Carlton Street. This option is shown in Figure 3. The routing of the BRT service would be modified from the LPA to include the additional length of tunnel and underground stations. Construction of the underground station between Carlton Street and St Mary’s Street would be relatively straightforward, but it relies on the BU buildings within the footprint being demolished as part of BU’s institutional masterplanning. Construction of the portal beneath the BU Bridge approach road would require careful phasing to ensure maintenance of traffic. The short length of tunnel between the portal and the underground station between Carlton Street and St. Mary’s Street would like be constructed using the sequential excavation method or by extending the cut and cover structures for the portal and station. The following are some of the key issues related to the BU Bridge Portal Option:

• As with the Mountfort Street Split Portal option, construction of the Urban Ring tunnel between the Green Line C Branch tunnel and the D Branch would likely require additional ground treatment and protective works.

• This option would entail construction impacts, ventilation structures, and station access at Audubon Circle, as well as at the D Branch Fenway Station.

• As with the Mountfort Street Split Portal, this option also reduces the flexibility of tunnel alignments for Urban Ring Phase 3.

• The proximity of the proposed tunnel portal in this option to the Commuter Rail line and the Grand Junction Rail Line and Beacon Park Rail Yard may offer opportunities for the removal of excavated material and supply of materials during construction.

• As with the Mountfort Street Split Portal option, the proposed tunnel alignment would eliminate the direct BRT connection with the Framingham/ Worcester commuter rail line at Yawkey Station.

• Operationally, this route offers a direct connection with the GJRR busway bridge without entering mixed traffic.

Recommendation: With appropriate planning and construction staging, the engineering and

construction issues of this option could be managed. Retain for further comparison to LPA and the

Landmark Portal with Fenway Station Option.

Performance

The benefits of the Landmark Portal with Fenway Station Option include a direct connection with the Green Line D Branch and an improved walk distance to the Green Line C Branch St Mary’s Street Station (500’ shorter than walking to the C Line at Kenmore). The Landmark Portal with Fenway Station Option provides somewhat higher ridership than the Landmark Portal Option because of improved Green Line D Branch and C Branch connections. It also eliminates the need for a connection into the congested Kenmore Square bus terminal.


The BU Bridge Portal Option also provides a direct connection with the Green Line D Branch, and does so by providing a headhouse from the south end of its Park Drive underground station. The north end of the same station can provide a headhouse at Audubon Circle with walk access to St. Mary’s station on the C Branch. The BU Bridge Portal Option provides no station stop at Yawkey. It achieves a faster travel time due to a combination of more direct routing and the higher speed of extending the busway tunnel. Ridership is higher than the Landmark Portal with Fenway Station Option due primarily to the higher travel speed. While the BU Bridge Portal Option provides better Green Line connectivity, it provides no direct connection with commuter rail and requires a longer walk distance to reach Yawkey Station from Audubon Circle. Costs

The added capital cost of the different options compared to the current LPA is shown in the table below. The BU Bridge Portal Option is significantly higher cost than the Landmark Portal Option or the Landmark Portal with Fenway Station Option due to additional length of tunnel and underground stations. Phase 3 Compatibility

The Landmark Portal with Fenway Station Option is same as the Landmark Portal Option: both could accommodate either Kenmore or Park Drive Phase 3 alignment. The BU Bridge Portal Option would only be consistent a Park Drive alignment for Phase 3, but would provide a longer tunnel for future conversion to Phase 3 operation.

Table 1

Summary Comparison of LPA Tunnel Options with LPA

LPA

Landmark

Portal with

Fenway

Station Option

BU Bridge

Portal Option

Infrastructure

Added Tunnel Length (feet) Base Same 2,080

Underground Stations 1 2 3

Green Line Connectivity

B Branch (walk distance/time) 1010’/3.8 min 1010’/3.8 min 790’/2.9 min

C Branch (walk distance/time) 1,640’/6.2 min 1,150’/4.4 min 840’/3.2 min

D Branch (walk distance/time) 1,640’/6.2 min 220’/0.8 min 220’/0.8 min

Commuter Rail Connectivity

Yawkey (walk distance/time) direct direct 1270 ft/5 min

Travel Time

LMA Station to Kendall Station 13 min 14 min 11 min

LMA Station to Harvard Square 18 min 19 min 16 min

Ridership 2030

BRT5, BRT6, BRT7 daily riders 135,320 +5% (approx.) +12% (approx.)

Cost

Capital Cost above LPA ($2007) Base $160 million $683 million

Phase 3 Alignment Choices

Kenmore or Park Drive

Kenmore or Park Drive

Park Drive

Conclusions

The Landmark Portal with Fenway Station Option provides a significantly improved Green Line connection, particularly for the D Branch, and provides increased ridership for a much lower incremental


cost than the BU Bridge Portal Option. It preserves the options of either a Kenmore or Park Drive alignment for Urban Ring Phase 3. However, the additional station stop does add to the travel time for some trips. By comparison, the BU Bridge Portal Option provides a further improvement to the Green Line connectivity for the C Branch, while being essentially the same as the Landmark Portal Option and the Landmark Portal with Fenway Station Option for Green Line D and B. It requires a longer walk distance to the commuter rail at Yawkey Station compared to either the Landmark Portal Option or the Landmark Portal with Fenway Station Option. The routing beneath Park Drive provides for more direct and faster travel times for key O/D pairs compared to the Landmark Portal Option or the Landmark Portal with Fenway Station Option, which route further east to reach Yawkey. However, the BU Bridge Portal Option limits the Phase 3 alignment to Park Drive and presents a significant engineering and construction challenge for tying in the relatively shallow profile of the Phase 2 west portal with a future Phase 3 tunnel alignment under the Charles River.

Memo –October 7, 2008 Page 8

Evaluation of LPA Tunnel Options

Figure 1

Landmark Portal with Fenway Station Option

Memo – October 7, 2008 Page 9


Figure 2

Mountfort Street Split Portal Option

Memo – October 7, 2008 Page 10


Figure 3

BU Bridge Portal Option


D-1 232551/01/G - November, 2008/D-1 of 3

Attachment D Current LPA Busway Tunnel


D-2 232551/01/G - November, 2008/D-2 of 3

D.1 Preliminary Plan and Profile Drawings

Drawing Title Sheet No.

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel (Western), STA W-0+00 – STA W-16+50

1T-W

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel (Western), STA W-16+50 – STA W-31+36.5

2T-W

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel (Western), STA W-31+36.5 – STA W-45+17.8

3T-W

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel (Central), STA C-0+00 – STA C-16+50

1T-C

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel (Central), STA C-16+50 – STA C-26+50

2T-C

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel (Central), STA C-26+50 – STA C-39+30.9

3T-C

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel (Eastern), STA E-0+00 – STA E-15+34.2

1T-E

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel (Eastern), STA E-15+34.2 – STA E-23+84.8

2T-E

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel (Eastern), STA E-23+84.8 – STA E-41+15.8

3T-E

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel, STA 39+30.9 – STA 56+36.5

4T

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel, STA 56+36.5 – STA 72+01

5T

Urban Ring Phase 2, Plan & Profile – Fenway, Boston LMA Tunnel, STA 72+01 – STA 86+27

6T


D-3 232551/01/G - November, 2008/D-3 of 3

D.2 Estimate of Truck and Rail Car Numbers During Construction

The histograms that follow illustrate an order of magnitude estimate of the number of trucks and or rail cars that would be required during construction. Individual histograms are presented for each construction site, followed by histograms that present the total numbers of trucks and rail cars arising as a result of the entire project.

The histograms are intended to provide an order of magnitude estimate commensurate with the current stage of the planning process, and are therefore calculated relative to the central alignment only. These estimates will need to be refined once the alignment is fully defined and preliminary engineering studies have been progressed. The use of rail transport and the identification of potential truck haul routes will require further study and coordination with the relevant authorities and agencies during subsequent stages of the planning process.

July

28,

200

8

Urb

an R

ing

Phas

e 2

– LP

A T

unne

l Es

timat

ed N

umbe

r of T

ruck

s/R

ail C

ars

per D

ay

Ass

umpt

ions

and

Not

es

ab

Ass

umpt

ions

: Th

e fo

llow

ing

tabl

e lis

ts s

ome

of th

e pr

inci

pal v

alue

s an

d as

sum

ptio

ns m

ade

in p

repa

ring

the

truck

/rail

car h

isto

gram

s:

Item

A

ssum

ed

Qua

ntity

U

nit

Bul

king

fact

or

1.3

Tr

uck

capa

city

- bu

lk m

ater

ials

30

yd

3 per

truc

k Tr

uck

capa

city

- se

gmen

t rin

gs

0.33

rin

gs p

er tr

uck

Truc

k ca

paci

ty -

tunn

el g

rout

16

eq

uiv.

yd3 p

er

truck

Tr

uck

capa

city

- ne

t wei

ght (

max

imum

) 34

to

ns p

er tr

uck

Rea

dy-m

ix C

oncr

ete

Truc

k 8

yd3 p

er tr

uck

Rai

l car

cap

acity

- bu

lk m

ater

ials

70

yd

3 per

car

R

ail c

ar c

apac

ity -

segm

ent r

ings

1.

0 rin

gs p

er c

ar

Rai

l car

cap

acity

- tu

nnel

gro

ut

60.0

eq

uiv.

yd3 p

er c

ar

Rai

l car

cap

acity

- ne

t wei

ght (

max

imum

) 10

0 to

ns p

er c

ar

Qua

ntiti

es a

re b

ased

on

the

porta

ls b

eing

con

stru

cted

usi

ng

perm

anen

t slu

rry w

alls

. An

addi

tiona

l 10%

(ins

itu) v

olum

e of

ov

erbr

eak

has

been

ass

umed

for t

he s

lurr

y w

all e

xcav

atio

n an

d co

ncre

ting

wor

ks.

For t

unne

ling

wor

ks, t

he fo

llow

ing

is a

ssum

ed:

o

The

tunn

el w

ill be

con

stru

cted

by

a 42

’-8” e

xcav

ated

di

amet

er e

arth

pre

ssur

e ba

lanc

e tu

nnel

bor

ing

mac

hine

(T

BM

). o

Th

e tu

nnel

lini

ng is

ass

umed

to h

ave

an in

tern

al d

iam

eter

of

39’-1

1”, a

thic

knes

s of

1’-9

” and

a ri

ng le

ngth

of 6

’-0”.

o

Pro

duct

ivity

ass

umed

to b

e 30

’ per

day

with

two

shift

s pe

r da

y, fi

ve d

ays

per w

eek.

Wee

kend

s us

ed fo

r TB

M

mai

nten

ance

, ext

endi

ng T

BM u

tiliti

es e

tc.

Ass

umed

wor

king

tim

e is

ten

hour

shi

fts, f

ive

days

per

wee

k fo

r po

rtal a

nd s

tatio

n co

nstru

ctio

n ac

tiviti

es.

Theo

retic

al in

situ

exc

avat

ion

volu

mes

are

mul

tiplie

d by

an

assu

med

bu

lkin

g fa

ctor

to g

ive

a bu

lked

vol

ume

of e

xcav

ated

mat

eria

l for

re

mov

al fr

om s

ite.

The

FHW

A m

axim

um g

ross

wei

ght l

imit

on th

e In

ters

tate

sys

tem

is

80,0

00 p

ound

s. T

ract

or/tr

aile

r wei

ght h

as b

een

assu

med

to b

e 12

,000

pou

nds

resu

lting

in a

max

imum

use

able

load

of 6

8,00

0 po

unds

(34

tons

). A

gen

eral

allo

wan

ce o

f fou

r tru

cks

per d

ay, p

er c

onst

ruct

ion

site

, has

be

en m

ade

to a

ccou

nt fo

r gen

eral

site

del

iver

ies,

incl

udin

g so

il co

nditi

onin

g, g

reas

e, a

nd o

ther

sup

plie

s fo

r TB

M tu

nnel

ing.

It is

as

sum

ed th

at tu

nnel

N

otes

: E

xcav

ated

dia

met

er o

f bor

ed tu

nnel

will

dep

end

on d

esig

n of

tunn

el

borin

g m

achi

ne a

nd is

sub

ject

to fu

rther

refin

emen

ts o

f the

cle

aran

ce

enve

lope

s.

Util

ity re

loca

tions

and

oth

er a

ssoc

iate

d w

orks

are

not

incl

uded

in th

e es

timat

es o

f dur

atio

ns a

nd q

uant

ities

. Th

e nu

mbe

r of t

ruck

s is

est

imat

ed a

nd w

ill v

ary

depe

ndin

g on

the

Con

tract

or's

mea

ns a

nd m

etho

ds.

Val

ues

show

n in

dica

te th

e to

tal n

umbe

r of t

ruck

s pe

r day

. Tru

ck

mov

emen

ts (i

.e. t

o an

d fro

m s

ite) w

ould

be

twic

e th

e va

lue

show

n.

Val

ues

are

base

d on

ave

rage

out

puts

ove

r act

ivity

dur

atio

n. P

eak

valu

es re

sulti

ng fr

om in

tens

e ac

tiviti

es (e

.g. c

oncr

ete

pour

s) o

r fro

m

incr

ease

d tu

nnel

ing

adva

nce

rate

s, w

hich

may

be

in e

xces

s of

100

’ pe

r day

, are

not

refle

cted

in th

is c

hart.

July

28,

200

8U

rban

Rin

g Ph

ase

2 - L

PA T

unne

lEs

timat

ed N

umbe

r of T

ruck

s pe

r Day

- La

ndm

ark

Cen

ter P

orta

lTr

uck

Onl

y O

ptio

n

ab

020406080100

120

Month

3

Month

6

Month

9Mon

th 12

Month

15Mon

th 18

Month

21Mon

th 24

Month

27Mon

th 30

Month

33Mon

th 36

Month

39Mon

th 42

Month

45Mon

th 48

Month

51Mon

th 54

Month

57Mon

th 60

Mon

th

Number of Trucks per Day

See

cove

r she

et fo

r ass

umpt

ions

and

not

es

July

28,

200

8U

rban

Rin

g Ph

ase

2 - L

PA T

unne

lEs

timat

ed N

umbe

r of T

ruck

s an

d R

ail C

ars

per D

ay -

Land

mar

k C

ente

r Por

tal

Truc

k an

d R

ail O

ptio

n

ab

020406080100

120

Month

3Mon

th 6

Month

9Mon

th 12

Month

15Mon

th 18

Month

21Mon

th 24

Month

27Mon

th 30

Month

33Mon

th 36

Month

39Mon

th 42

Month

45Mon

th 48

Month

51Mon

th 54

Month

57Mon

th 60

Mon

th


0102030405060

Number of Rail Cars per Day

Truc

ks

Rai

l Car

s

See

cove

r she

et fo

r ass

umpt

ions

and

not

es

July

28,

200

8U

rban

Rin

g Ph

ase

2 - L

PA T

unne

lEs

timat

ed N

umbe

r of T

ruck

s pe

r Day

- LM

A S

tatio

na

b

020406080100

120

Month

3

Month

6

Month

9Mon

th 12

Month

15Mon

th 18

Month

21Mon

th 24

Month

27Mon

th 30

Month

33Mon

th 36

Month

39Mon

th 42

Month

45Mon

th 48

Month

51Mon

th 54

Month

57Mon

th 60

Mon

th


See

cove

r she

et fo

r ass

umpt

ions

and

not

es

July

28,

200

8U

rban

Rin

g Ph

ase

2 - L

PA T

unne

lEs

timat

ed N

umbe

r of T

ruck

s pe

r Day

- Le

on S

tree

t Por

tal

ab

020406080100

120

Month

3

Month

6

Month

9Mon

th 12

Month

15Mon

th 18

Month

21Mon

th 24

Month

27Mon

th 30

Month

33Mon

th 36

Month

39Mon

th 42

Month

45Mon

th 48

Month

51Mon

th 54

Month

57Mon

th 60

Mon

th


See

cove

r she

et fo

r ass

umpt

ions

and

not

es

July

28,

200

8U

rban

Rin

g Ph

ase

2 - L

PA T

unne

lEs

timat

ed N

umbe

r of T

ruck

s pe

r Day

- A

ll Si

tes

Truc

k O

nly

Opt

ion

ab

020406080100

120

140

160

180

200

Month

3

Month

6

Month

9Mon

th 12

Month

15Mon

th 18

Month

21Mon

th 24

Month

27Mon

th 30

Month

33Mon

th 36

Month

39Mon

th 42

Month

45Mon

th 48

Month

51Mon

th 54

Month

57Mon

th 60

Mon

th


Rug

gles

/Leo

n S

t Por

tal S

iteLM

A S

tatio

n S

iteLa

ndm

ark

Cen

ter P

orta

l Site

See

cove

r she

et fo

r ass

umpt

ions

and

not

es

July

28,

200

8U

rban

Rin

g Ph

ase

2 - L

PA T

unne

lEs

timat

ed N

umbe

r of T

ruck

s an

d R

ail C

ars

per D

ay -

All

Site

sTr

uck

and

Rai

l Opt

ion

ab

020406080100

120

140

160

180

200

Month

3Mon

th 6

Month

9Mon

th 12

Month

15Mon

th 18

Month

21Mon

th 24

Month

27Mon

th 30

Month

33Mon

th 36

Month

39Mon

th 42

Month

45Mon

th 48

Month

51Mon

th 54

Month

57Mon

th 60

Mon

th


0102030405060708090100

Number of Rail Cars per Day

Truc

ks -

Rug

gles

/Leo

n S

t Por

tal S

ite

Truc

ks -

LMA

Sta

tion

Site

Truc

ks -

Land

mar

k C

ente

r Por

tal S

ite

Rai

l Car

s - L

andm

ark

Cen

ter P

orta

l Site

See

cove

r she

et fo

r ass

umpt

ions

and

not

es

Tunnel Technical Report

Documents

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