3.1.2 EXPLICIT ANALYSIS OF ROADSIDE SAFETY FEATURES · Roadside Safety Page 3.1.2.2 December 2009...

Geometric Design Guide for Canadian Roads

Page 3.1.2.1September 1999

3.1.2 EXPLICIT ANALYSISOF ROADSIDESAFETY FEATURES

3.1.2.1 What Does it Involve?

The design of the roadside environment is acomplex problem. Evaluating alternativedesigns and choosing between them is a difficulttask which involves degrees of uncertainty withrespect to the occurrence of collisions, theiroutcomes in terms of severity, and the real costsof the property damage, injuries, and fatalitieswhich can result. Nonetheless, as noted earlier,such analysis provides an explicit frameworkfor considering design trade-offs - a much moredesirable approach to roadside safety designthan meeting arbitrary “standards” whoseunderpinnings may or may not be appropriateto a given situation. Such a framework is also arequisite foundation for the value engineeringexercises which often form part of the roaddesign process.

An explicit framework for roadside safetyanalysis must necessarily recognize localagency needs, policies and practices within thespecifics of its approach. However, it is generallyaccepted that any such process will be built ontwo fundamental toolsets:

1. Predictive models which provide a way ofestimating collision frequencies andseverities under a wide variety ofconditions.

2. Cost-effectiveness models which providea way of quantifying the life-cycle costs (andbenefits) associated with any given set ofsafety measures.

Predictive models have been developed anddeployed by a number of agencies in NorthAmerica. While the latest AASHTO RoadsideDesign Guide4 probably represents the mostcurrent and widely accepted effort in this regard,designers should be aware that the state of theart in this area is continually developing andshould be monitored regularly for new modelsand techniques which may have application totheir design challenges. The techniquespresented in this Guide are founded in part on

the AASHTO work, but also recognize a numberof practices drawn, where possible, from theCanadian context.

The techniques of cost-effectiveness analysisare well established and are applied for a varietyof purposes in transportation and highwaydesign agencies. There are a number ofalternative approaches that are available butmost commonly, the tools used bytransportation agencies are built on life-cyclecosting models and use present worth orannualized cost techniques as their underlyinganalysis methodology. All of these approachesare built on fundamental assumptions regardingparameters such as discount rates and unitcollision costs. In order to enforce consistentand comparable results across thetransportation agency, these basic assumptionsare usually set as a matter of policy andrepresent a “given” for designers to use in theiranalyses.

3.1.2.2 Overview of CollisionPrediction Models

Predictive models are used to provide at leastthree levels of information to the designer:

1. Estimates of the numbers ofencroachments – an errant vehicle leavingthe roadway – likely to occur. Designersmust recognize that these estimates areprobabilistic in nature, in spite of thedeterministic form which they often takeand make appropriate provisions in theirroadside designs for this fact. Additionaldiscussion of this issue is provided later inthis chapter.

2. Estimates of the number of collisions likelyto occur as a result of the encroachments.Every encroachment does not necessarilyresult in a collision, since a number ofvehicles will normally recover within acertain distance without incident. Criticalfactors used in these models include: theangle of departure from the roadway, thespeed of the vehicles involved, and the typeof vehicles involved. Again, the probabilisticnature of these models must be kept inmind.

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Page 3.1.2.2 December 2009

3. Estimates of the severity of the collisionswhich occur. Once an estimate of thenumber of collisions which can be expectedto occur at a given location is available, thisis usually converted into an equivalent dollarcost through the use of a parameter suchas a Severity Index (SI). This parameterusually varies with the speed and type ofvehicle, the angle of incidence of thecollision, and the type of object struck.Different scales are used by differentagencies in estimating severity indices,however both AASHTO4 and NCHRP5

provide representative sets of theseindices.

Additional discussion on these concepts,suggested models for their application, andworked examples of their use are provided insubsequent sections of this Guide.

3.1.2.3 Overview of Cost-Effectiveness Analysis

Transportation agencies have traditionally usedcost-effectiveness analysis models to addressmany different types of investment decisions,including the analysis of site-specific alternativesafety treatments. AASHTO, TAC, Provincialand State Transportation Agencies, andindependent research efforts have allcontributed to the state of knowledge in the useof these techniques. The engineering economyaspects of such models are usually based onlife-cycle cost analysis, and designers mustconsider that analysis outcomes can besubstantively influenced by assumptions withrespect to both the specific technique used, andmany of the basic input parameters. In manyinstances, a number of input parameters(discount rates; monetary values to be used forfatalities, personal injury and property damagetypes of collisions, etc.) should be defined inagency policy, reviewed on a regular basis toensure their appropriateness, and revised anddeployed promptly in order to ensureconsistency with the agency and politicalobjectives which necessarily influence suchsafety investment decisions.

3.1.2.4 Integrated Roadside SafetyCost-EffectivenessAnalysis

Introduction

Many agencies have developed integratedapproaches to roadside safety cost-effectiveness analysis 4, 6, 13, 17. In general, all ofthe approaches involve four distinct elements:

• an encroachment module: to estimate theexpected encroachment frequency givenroad and traffic data

• a collision prediction module: to assess ifan encroachment would result in a crash

• a severity prediction module: to estimatethe severity and estimated costs for eachcrash

• a benefit-cost module; to calculate theincremental benefit/cost ratios betweeneach pair of safety alternatives

A typical example of the structure of such anapproach is described below, based on theRoadside Safety Analysis Program6 (RSAP)process.

Benefit-Cost Analysis Overview

Benefit-cost analysis is an analytical approachto solving problems of choice. To carry out theanalysis, objectives must be defined, alternativeways of achieving each objective need to beidentified, and for each objective, the alternativewhich yields the required level of benefits at thelowest cost are determined.18 Strictly speaking,the term cost-effectiveness analysis is oftenused as a synonym for benefit-cost techniqueswhen the benefits or outputs of the alternativescannot be quantified in terms of dollars.However, more recently, the two terms havebeen used interchangeably, and road safetycost-effectiveness analysis techniquesuniformly quantify outputs in monetary terms.In addition, the road safety use of the term “cost-effectiveness” analysis generally also impliesa suite of techniques incorporating the fourmodules noted above.


.1.3.5December 2009

Radius Design Speed(m) 60 70 80 90 100 110 +900 1.1 1.1 1.1 1.2 1.2 1.2700 1.1 1.1 1.2 1.2 1.2 1.3600 1.1 1.2 1.2 1.2 1.3 1.4500 1.1 1.2 1.2 1.3 1.3 1.4450 1.2 1.2 1.3 1.3 1.4 1.5400 1.2 1.2 1.3 1.3 1.4350 1.2 1.2 1.3 1.4 1.5300 1.2 1.3 1.4 1.5 1.5250 1.3 1.3 1.4 1.5200 1.3 1.4 1.5150 1.4 1.5100 1.5

Note: The clear zone horizontal curve adjustment factor is applied to the outside of curves only.Curves flatter than 900 m do not require an adjusted clear zone.

3. On unshielded, traversable 3:1 slopes,determination of the width of the recoveryarea at the toe of slope should take intoconsideration right-of-way availability,environmental concerns, economic factors,safety needs, and collision histories. Inaddition, the distance between the edge ofthe travel lane and the beginning of the 3:1slope should influence the recovery areaprovided at the toe of slope.

4. Increasing inadequate superelevation oncurves provides an alternative way ofincreasing road safety within a horizontalcurve except where snow and iceconditions limit the use of such increases.

5. Applying the clear zone concept on flat andlevel roadsides is relatively simple. In fill orcut sections where roadside slope may beeither positive, negative or variable, orwhere roadside channels exist, the situationis more problematic. Designers should referto the discussions of Section 3.1.4 foradditional guidance in such situations.

Table 3.1.3.2 Horizontal Curve Adjustments for Clear Zone Distances4

sufficient by themselves to define the designdomain for the clear zone. These numbers mustbe applied in the context of situation-specificfactors and good design practice. The followingdesign heuristics are included as one meansof illustrating such practice and providingadditional definition to the design domain forthis parameter:

1. The figures in Table 3.1.3.1 provide only aframework for the designer to work with inlooking at ranges of clear zone dimensionsto use. They are not absolute, and must beconsidered in the context of site-specificconditions and practicality.

2. The evaluation of alternative clear zonedesign approaches should be carried outusing a well-defined cost-effectivenessanalysis procedure such as that providedby AASHTO’s “Roadside” procedure andrelated software available with the 1996AASHTO Roadside Design Guide, themore recent FHWA developed successorto Roadside, called RSAP or other similarprocedures. Such analyses would normallyconsider alternatives, such as the use ofroadside barrier, if provision of therecommended clear zone is not costeffective.

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Benefit-Cost Analysis for Clear Zone: Example

This example calculation illustrates the application of benefit-cost analysis using a manual techniqueemployed by the Ministry of Transportation of Ontario in their Prioritized Contract Content Guidelines17.While this technique differs in approach in terms of collision cost determinations from that describedpreviously, it is equally valid and produces a similar incremental benefit-cost analysis result thatallows for the explicit evaluation of safety consequences.

Problem Statement:

A rigid base luminaire support (concrete pole) is located 3.0 m from the edge of pavement, which isalso the edge of the through lane. Since the hazard is within the clear zone this pole must be eitherrelocated, shielded or made forgiving. Determine the most cost-effective of the following treatments:

A. leave the pole as isB. replace the pole with a breakaway base poleC. relocate the pole outside the clear zoneD. protect the pole with a roadside barrier

Given:

• two-lane undivided rural highway• 3.5 m lanes, unpaved shoulders• design speed: 90 km/h• AADT: 10,000 (50:50 directional split)• sideslopes: 5:1• clear zone requirement 9.0 m, Table 3.1.3.1• traffic growth rate: 0%• encroachment rate: 0.00045 events/km/year• concrete pole diameter: 0.5 m• projected service life: 10 years• breakaway base pole cost: $5,000 (Alternative B)• relocation cost: $11,000 (Alternative C)• relocation distance: 6.0 m (9.0 m total from the edge of pavement)• protection cost: $11,500 (Alternative D)• POLICY CRITERIA: If more than one alternative has B/C ratio greater then 2.0, an incremental

benefit/cost analysis is required to determine which alternative is most cost-effective.

Collision Frequency Model:

Cf = (E

f/2000) [(L+19.2) P [Y>A] + 5.14∑P [Y> (A+1.8+ (2J-1)/2)]]

Where:

Cf

= collision frequency (collisions/year)E

f= number of encroachments/year/direction

L = horizontal length of the roadside obstacle (m)W = width of obstacle (m)A = lateral distance of the roadside object to edge of pavement (m)P[Y>..] = probability of a vehicle lateral displacement greater than some valueJ = the number of 1.0 m wide obstacle-width increments (the number of J units equal to W rounded to the nearest whole number)



∑ = mathematical summation with summation index range from J = 1 to J=W (in 1.0 m steps)

Calculations:

For all alternatives

Ef

= encroachment rate x directional split x ADTE

f= (0.00045)(0.5)(10,000) = 2.25 collisions/km/direction

Alternative A: Do Nothing

First, calculate the collision frequency from:

Cf

= (Ef/2000)[(L+19.2)P[Y>A]+5.14∑P[Y>(A+1.8+(2j-1)/2)]]

with: L = 0.5 mA = 3.0 m (adjacent lane), A = 6.5 m (opposite lane)W = 1.0 m (rounded to nearest m)

Cf

= (2.25/2000[(0.5+19.2)(0.56) + (5.14)(0.36)] + (2.25/2000)[0.5+19.2)(0.3) + (5.14)(0.21)]= 0.022 collisions/year

Notes: 1. the probabilities (P[Y...]) come from MTO source material13.2. both encroachment directions combined.

Now, calculate the annual cost of collisions:

CCA

= Cf x cost per collision

CCA

= (0.022 collisions/year)($162,000/collision)= $3,564 per year

Note: unit collision cost for concrete pole, $162,000, is derived from the severity index: 5.5.

Now, convert the annual cost to a net present value:

NPVA

= CCA(P/A, discount rate, traffic growth, service life)

Note: (P/A,...) from MTO Source Material17

NPVA

= $3,564 (P/A, 6%, 0% growth, 10 years)= $26,231

Alternative B: Replace

For this alternative, the collisions per year remain at 0.022 and the severity index for a breakawaypole reduces to 2.8, reducing the unit collision cost to $13,800.

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CCB

= 0.022 x $13,800= $304 per year

then:

NPVB

= $304 (P/A, 6%, 0% growth, 10 year life)NPV

B= $2,237

Alternative C: Relocate

In this alternative, the relocation increases the distance between the road and the pole, reduces theprobability of a collision taking place, and reduces the collision rate to 0.011 collisions/year. Theseverity index, 5.5, and the unit collision cost, $162,000 remain the same since the concrete pole isretained. Calculating this alternative gives:

CCA

= 0.011 x $162,000= $1,782 per year

then:

NPVC

= $1,782 (P/A, 6%, 0% growth, 10 year life)NPV

C= $13,115

Alternative D: Protect

In this alternative, the probability of collisions increase because of the greatly increased length ofobstacle presented by the barrier and its location relative to the road. The collision rate increases to0.059 collisions/year. The severity index is reduced to 3.0, reducing the unit collision cost to $15,088due to the nature of the new obstacle (traffic barrier as opposed to a concrete pole). Calculating thisalternative gives:

CCD

= 0.059 x $15,088= $890 per year

NPVD

= $890 (P/A, 6%, 0% growth, 10 year life)NPV

D= $6,552

Now the benefit-cost analysis can be carried out based on the summary of alternatives below:

Alternative Net Present Value annual collision cost

Installation Cost (Given)

A B C D

$26,231 $2,237 $13,115 $6,552

$5,000 (in 10 years) $5,000 (now) $11,000 (now) $11,500 (now)

Using A as the base case the following relative benefits and costs can be calculated:


Page 3.1.4.7December 2009

Discussion:

The available clear zone distance is 1.8 m, 0.2 to 1.2 m less than the recommended recovery area.When an area has a significant number of run-off-the-road collisions, it may be appropriate to considershielding or removing the tree within the collision area. If this section of road has no significantcollision history and is heavily forested with most of the other trees only slightly farther from the road,this tree would probably not require treatment. However, if none of the other trees are closer to theroadway than, for example 4.5 m, this individual tree represents a more significant hazard and shouldbe considered for removal. If a tree were 4.5 m from the edge of the travelled way, and all or most ofthe other trees were 7.5 m or more, its removal might still be appropriate. This example emphasizesthat the clear zone distance is an approximate number at best and that individual objects should beanalyzed in relation to other nearby obstacles.

EXAMPLE B4

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Page 3.1.4.8 September 1999

Discussion:

Since the non-recoverable slope is within the required clear zone distance of the 10:1 slope, a runoutarea beyond the toe of the non-recoverable slope is required. Using the steepest recoverable slopebefore or after the non-recoverable slope, a clear zone distance is selected from Table 3.1.3.1. Inthis example, the 8:1 slope beyond the base of the fill dictates a 9.0 to 10 m clear zone distance.Since 5.0 m are available at the top, an additional 4.0 to 5.0 m should be provided at the bottom. Allslope breaks should be rounded and no fixed objects would be built within the upper or lower portionsof the clear zone or on the intervening slope.

EXAMPLE C4



Discussion:

Since the critical slope is only 7.0 m from the travelled way, instead of the suggested 9.0 to 10.5 m,it should be flattened or shielded.

EXAMPLE D4

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EXAMPLE E6

Discussion:

The available 1.5 m is 0.5 to 1.5 m less than the recommended recovery clear zone. If much of thisroadway has a similar cross section and no significant run-off-the-road collision history, neither slopeflattening nor a traffic barrier would be recommended. On the other hand, even if the 5:1 slope was3.0 m wide and the clear zone requirement was met, a traffic barrier might be appropriate if thislocation had noticeably less clear zone than the rest of the road and the embankment was unusuallyhigh.


Page 3.2.iSeptember 1999

3.2 ACCESS

3.2.1 INTRODUCTION .......................................................................................... 3.2.1.1

3.2.1.1 General .......................................................................................... 3.2.1.13.2.1.2 Access Management and Safety ................................................... 3.2.1.23.2.1.3 Building Set-Back Guidelines ........................................................ 3.2.1.53.2.1.4 Pedestrian Considerations ............................................................ 3.2.1.63.2.1.5 Capacity Considerations ................................................................ 3.2.1.6

3.2.2 ACCESS MANAGEMENT AND FUNCTIONAL CLASSIFICATION ............ 3.2.2.1

3.2.2.1 Access Types ................................................................................ 3.2.2.13.2.2.2 Access Classification System ........................................................ 3.2.2.2

3.2.3 ACCESS MANAGEMENT BY DESIGN CLASSIFICATION ........................ 3.2.3.1

3.2.3.1 Freeways ....................................................................................... 3.2.3.13.2.3.2 Expressways ................................................................................. 3.2.3.13.2.3.3 Arterials ......................................................................................... 3.2.3.23.2.3.4 Collectors ....................................................................................... 3.2.3.23.2.3.5 Local Roads ................................................................................... 3.2.3.3

3.2.4 ACCESS CONFIGURATION ....................................................................... 3.2.4.1

3.2.4.1 Distance from Curves .................................................................... 3.2.4.13.2.4.2 Distance from Bridges ................................................................... 3.2.4.13.2.4.3 Distance from Interchanges and Intersections .............................. 3.2.4.13.2.4.4 Distance from Railways ................................................................. 3.2.4.13.2.4.5 Geometry ....................................................................................... 3.2.4.13.2.4.6 Intersection and Crossing Sight Distance ..................................... 3.2.4.13.2.4.7 Gradients ....................................................................................... 3.2.4.23.2.4.8 Skew Angles .................................................................................. 3.2.4.23.2.4.9 Turning Radii ................................................................................. 3.2.4.23.2.4.10 Auxiliary Lanes .............................................................................. 3.2.4.23.2.4.11 Signalized Access Spacing ............................................................ 3.2.4.2

3.2.5 CONTINUOUS RIGHT-TURN AUXILIARY LANESON DIVIDED ARTERIALS ........................................................................... 3.2.5.1

3.2.5.1 General .......................................................................................... 3.2.5.13.2.5.2 Design Elements ........................................................................... 3.2.5.5

3.2.6 TWO-WAY LEFT-TURN LANES .................................................................. 3.2.6.1

3.2.6.1 General .......................................................................................... 3.2.6.13.2.6.2 Width ............................................................................................. 3.2.6.33.2.6.3 Application ..................................................................................... 3.2.6.3

Access

Page 3.2.ii December 2009

3.2.7 SERVICE (FRONTAGE) ROADS ................................................................ 3.2.7.1

3.2.7.1 General .......................................................................................... 3.2.7.13.2.7.2 One-Way Service (Frontage) Roads ............................................. 3.2.7.23.2.7.3 Two-Way Service (Frontage) Roads ............................................. 3.2.7.3

3.2.8 CORNER CLEARANCES AT MAJOR INTERSECTIONS......................... 3.2.8.1

3.2.8.1 General .......................................................................................... 3.2.8.13.2.8.2 Suggested Minimum Corner Clearance Dimensions .................... 3.2.8.1

3.2.9 DRIVEWAYS ................................................................................................ 3.2.9.1

3.2.9.1 General .......................................................................................... 3.2.9.13.2.9.2 Operational Considerations ........................................................... 3.2.9.13.2.9.3 Sight Distance ............................................................................... 3.2.9.23.2.9.4 Turning Characteristics ................................................................. 3.2.9.43.2.9.5 Width ............................................................................................. 3.2.9.63.2.9.6 Angle of Driveway .......................................................................... 3.2.9.63.2.9.7 Corner Clearances at Minor Intersections ..................................... 3.2.9.63.2.9.8 Spacing of Adjacent Driveways ...................................................... 3.2.9.73.2.9.9 Spacing Considerations for Driveways on

Opposite Sides of the Road .......................................................... 3.2.9.93.2.9.10 Clear Throat Lengths ................................................................... 3.2.9.113.2.9.11 Grades ......................................................................................... 3.2.9.113.2.9.12 Pedestrian Crossing Considerations ........................................... 3.2.9.14

3.2.10 CULS-DE-SAC ........................................................................................... 3.2.10.1

REFERENCES ...................................................................................................... 3.2.R.1

Tables

Table 3.2.1.1 Effect of Control of Access on Collisions and Fatalitiesin Urban and Rural Areas ............................................................... 3.2.1.2

Table 3.2.2.1 Access Categories Keyed to Road Type ....................................... 3.2.2.3Table 3.2.5.1 Advantages and Disadvantages of Continuous Right-Turn

Auxiliary Lanes for the Provision of Access Along DividedArterial Roads ............................................................................... 3.2.5.5

Table 3.2.6.1 Advantages and Disadvantages of Two-Way Left-Turn Lanes ..... 3.2.6.4Table 3.2.7.1 Advantages and Disadvantages of Service Roads Adjacent

to and Paralleling a Major Urban Road ......................................... 3.2.7.2Table 3.2.9.1 Typical Driveway Dimensions ........................................................ 3.2.9.7Table 3.2.9.2 Maximum Number of Driveways Based on Property Frontage ... 3.2.9.11Table 3.2.9.3 Suggested Minimum Clear Throat Lengths for Major Driveways 3.2.9.12



The following is an example of a seven levelaccess category system5:

• Access Level 1; access via interchangeswith public roads only

• Access Level 2; access via at-grade publicroad intersections or at interchanges

• Access Level 3; right-turn access drivewayonly

• Access Level 4; right and left-turn accessin, right-turn access out

• Access Level 5; right and left-turn accessinto and out of an activity centre – left-turnlanes required

• Access Level 6; right and left-turn accessinto and out of an activity centre – left-turnlanes optional

• Access Level 7; right and left-turn accessinto and out of activity centre – drivewayspacing limited by safety requirements only

The seven access levels may be modified toreflect design practices of specific agencies.

A general approach to assigning accesscategories or levels to a road system is givenin Table 3.2.2.1. This table shows how each ofthe seven types of allowable access relates tothe six basic road classes – freeways,

expressways, major arterials, minor arterials,collectors, and local roads, and the generaldesign features associated with each class.

It can be seen from the table that direct propertyaccess is prohibited from freeways andexpressways, access levels 1 and 2. Directproperty access should be denied or restrictedfrom access levels 3 and 4, major arterials,respectively. However, access may be providedwhere no reasonable alternative access isavailable, or where it is in the general publicinterest to do so. Where access must beprovided, it should be limited to right turns onlyfor access level 3, and to right- and left-turnentry and right-turn exit for access level 4. Directproperty access may be permitted for accesslevels 5 and 6; it is desirable at level 7.

Higher access categories can be selected forrural and suburban areas or new corridorswhere existing strip development has not yeteroded the function of the road. In areas withexisting high density development, theassignment of lower categories and therefore,lower or ambient standards may be morepractical. Keep in mind, however, that inexisting high development corridors where thereis support for improving mobility and safety, ahigher standard can be selected and over time,the redevelopment in the corridor will reflect thathigher standard. In general, for each roadsegment, the highest standard which can beimplemented should be selected.

Table 3.2.2.1 Access Categories Keyed to Road Type

AccessCategory

Road Classification Direct Property Access General Design Features

1 Freeway No Multilane, Median2 Expressway No Multilane, Median3 Major Arterial Restrict or Denya Multilane, Median4 Major Arterial Restrict or Denyb Multilane, Medianc

5 Minor Arterial Yes Multilane, or 2 Lanes6 Collector Yes 2 Lanes7 Local/Frontage Yes 2 Lanes

Note: a. Right turns only when provided.b. Right and left turn entry and right turn only exit when provided.c. Might be two-lanes in some rural areas.

Access




Notes: a. Ld (min) is normally increased where storage of vehicles is a typical requirement,due to pedestrian movements or vehicle queuing in the entrance.

b. The Ld (min) and La distances based on grades of 2 percent or less.c. Refer to Table 3.2.9.3 for minimum throat lengths.d. Straight taper, without curves, also acceptable.

Figure 3.2.5.2 Auxiliary Lane Mid-Block Access for Major Developments

Access


Figure 3.2.5.3 Typical Auxiliary Lane Introduction and Termination



Figure 3.2.5.7 Simple Radius Intersection Arrangement With One-Way AngledAccesses Along Auxiliary Lane of a Divided Arterial

Access




• the two-way left-turn lane is on a multi-lanearterial roadway with frequent signalizedintersections

Overhead signs are typically placed at one-quarter or one-half points between major crossroads. They are positioned a minimum of 50 maway from the intersections to assist inadequate visibility.

Two-way left-turn lanes are generally notextended through a major intersection. They areterminated prior to the intersection and replacedwith a single exclusive left-turn lane. Appropriatepavement markings or divisional islands shouldbe used to terminate the two-way left-turn lanein advance of the exclusive left-turn lane at themajor intersection.

3.2.6.2 Width

Widths for 2WLTLs are generally the same asthe adjacent through lane, but not less than3.5 m for design speeds equal to or less than60 km/h. A width of 4.0 m is desirable for designspeeds greater than 60 km/h. The additionalwidth over the adjacent lane recognizes thatvehicles are making turning manoeuvres fromboth directions simultaneously, and adds ameasure of safety. Widths greater than 5.0 mare generally avoided due to operationalproblems.

3.2.6.3 Application

Since opportunities for a left-turning vehicle todecelerate within the limits of a 2WLTL may berestricted by access spacing and the potentialfor conflicting vehicle movements, a 2WLTL isbest suited for urban roads with operatingspeeds of 50 to 60 km/h. Operating speeds upto 70 km/h may be tolerated where most otherconditions are favourable.

Two-way left-turn lanes operate successfullyover a wide range of arterial road volumes. Asurvey of major Canadian cities indicatessuccessful operation of 2WLTLs for arterialroads with volumes of up to 35 000 veh/d anda seven-lane cross section. The successfuloperation is the result of a number of interrelatedfactors including:

• horizontal and vertical alignments

• sight distance

• cross section dimensions

• through traffic volumes

• Ieft-turning traffic volumes

• frequency of traffic signals

• frequency of cross roads

• frequency of accesses

• driver familiarity

Due to the complexity and number of designfactors to be considered at any specific site, itis difficult to stipulate a set of limiting conditionsfor the effective operation of 2WLTLs. Thephysical conditions at each potential site arenormally examined by experienced geometricdesign and traffic operations personnel, andengineering judgement is used to determine thepotential for and improvements required tosuccessfully implement a 2WLTL.

Two-way left-turn lanes may be prone toimproper use, particularly in jurisdictions wherefew 2WLTLs exist and driver unfamiliarity is aproblem. Some of the potential operationalproblems are as follows:

• vehicles may make angle turns across the2WLTL, leaving the rear of the turningvehicle encroaching into the adjacentthrough lane while waiting for a gap tomerge with or cross the through trafficstream

• left-turning vehicles may enter the 2WLTLtoo far in advance of the access where theleft turn is to be made, and thereby impedeor risk collision with opposing left-turningtraffic in the 2WLTL

• through vehicles may use the 2WLTL as apassing lane to overtake slower movingtraffic in the through lanes

• left-turning vehicles may not use the 2WLTLto decelerate from the operating speed ofthe arterial, but decelerate substantially inthe through lane before entering the 2WLTL

Access


• cyclists may perceive the 2WLTL as arelatively protected area, and ride along itfor long distances

• pedestrians may be placed at a greater risk,due to the wide cross section and the lackof a physical refuge area

Proper education and enforcement programscan be effective to achieve a significantreduction in improper use. The generaladvantages and disadvantages of 2WLTLs aresummarized in Table 3.2.6.1.

Explicit Evaluation of Safety

Two-way left-turn lanes (2WLTLs) diminishconflicts with vehicles turning left from the mainroadway and provide a refuge for vehiclesturning left onto the main road. Approximatelyhalf of the collisions involving vehicles enteringor exiting driveways are associated with left-turn manoeuvres. Almost all research articlesrelating to the safety effect of 2WLTLs are formulti-lane roadways in urban and suburbansettings. The relationship between the reduction

in number of collisions versus the density ofaccess points is given by Equation 3.2.1:

CMF = 1-0.35 (0.0047X + 0.0039X2)/(0.745 + 0.0047X + 0.0039X2) (3.2.1)

where CMF = the Collision ModificationFactor

X = the number of access pointsper kilometre (total of bothdirections)

The Collision Modification Factor for 2WLTLsis depicted graphically in Figure 3.2.6.2.

For example, if there are 24 driveways on a1.5 km section of undivided roadway, thenumber of driveways per kilometre is 24/1.5 or16 access points per kilometre. By using eitherEquation 3.2.1 or Figure 3.2.6.2, the CollisionModification Factor is determined to be 0.79.The percentage reduction in collisions whichcould be anticipated if a 2WLTL was installedwould be (1-0.79) x 100 = 21%. The cost ofinstalling a two-way left-turn lane can becompared to the benefit of the reduction incollision costs to determine the advisability ofthe installation.

Table 3.2.6.1 Advantages and Disadvantages of Two-Way Left-Turn Lanes

Advantages Disadvantages

• well suited to strip development withfrequent low to medium volume driveways

• remove turning traffic from the throughlanes, significantly improving traffic safetyand capacity

• not as restrictive to access as a raisedmedian

• implementation costs and right-of-wayrequirements are less than that of a raisedmedian

• generally not suited for operating speeds>70 km/h

• not suitable to high volume driveways,exclusive turn lanes preferred

• left-turn paths not clearly defined andturning conflicts can occur

• limited to tangent alignments with goodsight distance

• traffic level of service lower as comparedto divided roadway

• opposing traffic flow not physicallyseparated as with a raised median

• pedestrians required to cross wideroadway without a physical centralrefuge area

• operation may not be clearly understoodby the unfamiliar driver



Figure 3.2.8.2 Suggested Minimum Corner Clearances to Accesses or PublicLanes at Major Intersections

d

d

Access


roadway. As a minimum, B is equal to or greaterthan the storage length, but desirably B is equalto or greater than the storage length plus thebay taper.

The lower half of Figure 3.2.8.2 presentssuggested minimum corner clearancedimensions adjacent to an intersection with stopcontrol, rather than signals, at the cross road.Dimensions F and H are applicable to anundivided roadway, G and J to a divided road.Dimensions F and J are based on right-turningvehicles at the intersection being able toperceive and react to a conflict at the firstaccess. Dimension H is based on providingspace for three passenger vehicles to bequeued at the stop control without blocking the

driveway. Dimension G is based on the samephilosophy as dimension B in the upper half ofthe figure.

The lesser values shown on Figure 3.2.8.2 forcollector and local roads reflect the reducedneeds associated with lower traffic volumes anda decreased expectation in level of service.

Due to small corner parcel sizes and the legalrequirements for access provision, it may notbe feasible to provide the suggested minimumcorner clearances. Engineering judgement anda good understanding of traffic operations areneeded to determine the most suitable accesslayout and related roadway provisions for theprevailing conditions.



corner clearance. A minimum dimension (C) of5.0 m is suggested to separate the conflictzones and to provide for a greater manoeuvringarea for turning trucks. For an industrial area,this then results in a minimum corner clearanceof about 25.0 m (11.0 m for the minimum cornercurb radius, the 5.0 m dimension (C), and a9.0 m minimum driveway curb radius).

A high volume driveway on the near side of anintersection may warrant a left-turn storage areaon the roadway to accommodate left turningtraffic into the driveway. If this is the case, thedriveway is located in consideration of the totaldistance needed for the back-to-back left-turnbays created on the roadway. The combinedleft- turn storage and taper requirementssignificantly increases the corner clearancerequirements.

3.2.9.8 Spacing of AdjacentDriveways

In addition to the corner clearanceconsiderations described in Subsection 3.2.9.7,driveways are normally located in considerationof their physical relationships to existing orpossible future driveways. The following threecriteria need to be considered:

• minimum spacing between driveways

• minimum offset to property line

• maximum number of driveways based onproperty frontage

The application of these design criteria assistsin meeting the following objectives:

• to clearly identify to the user which propertyeach driveway serves

• to ensure that sufficient space is availablebetween driveways for the positioning oftraffic signs, lighting poles and other surfaceutility fixtures, and road hardware

• to separate the conflict areas for eachdriveway

• to provide appropriate space betweendriveways for on-street parallel parking,where permitted and in consideration ofsight line requirements

• to increase the length of potentially collisionfree pedestrian areas by minimizing thenumber and width of driveways

Roadway retrofit projects often provide theopportunity to improve existing drivewayspacing.

The minimum spacing between driveways ismeasured between the end and start of the curbreturns on the adjacent driveways, shown asdimension (E) on Figure 3.2.9.3. A 1.0 mminimum spacing is recommended betweenadjacent low volume driveways for residentialproperties, along local and collector roadways,while a 3.0 m minimum is the suggesteddimension for both commercial and industrial

Land UseDimension(m) Residential Commercial Industrial

width (W)

• one-way

• two-wayright-turn radius (R)

3.0a – 4.33.0.a – 7.33.0 – 4.5

4.5a – 7.57.2 a – 12.0 b

4.5 – 12.0

5.0 a – 9.09.0 a – 15.0 b

9.0 – 15.0

Notes: a. Minimum widths are normally used with radii at or near the upper end of thespecified range.

b. Increased widths may be considered for capacity purposes; where up to 3 exitlanes and 2 entry lanes are employed, 17.0 m is the max. width, exclusive of anymedian.

c. Applicable to driveways only, not road intersections.

Table 3.2.9.1 Typical Drivewayc Dimensions

Access


Figure 3.2.9.3 Driveway Spacing Guidelines - Locals and Collectors

0b or R 0b or R



Where inter-development traffic is expected tobe significant, and signalization of the drivewayintersection is not desirable, the manoeuvrerequired to cross the entire width of a busyroadway in a single continuous movement maybe difficult. In this case, it is often advantageousto offset the opposing driveways to eliminatethe concentrated conflict zone. A minimumoffset of 100 m between driveway centrelinesis desirable, as illustrated in Figure 3.2.9.4. Thistechnique does, however, increase the numberof slow moving vehicles making ingress, egressand weaving manoeuvres on the roadway,which may present other operational concerns.The relative impact is assessed to determinethe best design decision.

Retrofitting of existing driveway locations maybe warranted over time as traffic conditionschange along a roadway and at individualdriveways. Alternatives to existing drivewaylocations, or driveway consolidation to improvespacing, may provide effective solutions totraffic operational concerns.

3.2.9.10 Clear Throat Lengths

In order for major driveways to operateefficiently, both from the road side and internally,it is desirable to provide a no conflict and storagezone within the driveway. This zone iscommonly referred to as the clear throat lengthor set-back distance and is measured from theends of the driveway curb return radii at theroadway and the point of first conflict on-site.Figure 3.2.5.2 illustrates how a throat length ismeasured. Failure to provide sufficient throatdistance results in frequent blocking of on-site

circulation roads which can in turn createqueues of entering vehicles. The provision ofappropriate clear throat length or storage spaceis particularly important for drive-in servicedevelopments where the customers remain intheir vehicles while waiting to be served. Thesetypes of developments include drive-inrestaurants and banks, automatic car washes,and parking facilities with entry control.

For large developments, the appropriate throatlength is best determined by a detailed trafficanalysis based on the traffic control providedat the road and the anticipated volumes andtypes of traffic. Table 3.2.9.37 is a guideline forsuggested minimum clear throat lengths forvarious types of developments.

3.2.9.11 Grades

When selecting the most suitable grades for adriveway, a number of considerations areimportant including:

• road classification

• driveway volume

• maximum grade for the driveway within theright of way where it intersects the roadway

• minimum grade for the driveway within thissame zone

• maximum driveway grade on-site

• maximum rate of grade change

• pedestrian crossing cross-slope

Table 3.2.9.2 Maximum Number of Driveways Based on Property Frontage9

Frontage (m) Maximum Number of Drivewaysa

15 16 – 50

51 – 150 > 150

1b 2 3c

4 or morec

Notes: a. Subject to spacing guidelines presented in Subsections 3.2.5.2 and in Figure 3.2.9.3. b. Single family residential properties normally restricted to one driveway, irrespective of frontage. c. For large developments the location and design elements of driveways are normally

determined by a detailed traffic impact study.

Access


• roadway, driveway, roadside and propertydrainage

• cyclist accommodation

Desirable maximum grade changes, betweenthe roadway cross-slope and the drivewaygrade, vary in accordance with the roadclassification. For the higher classification road,it is desirable to minimize the grade change atthe roadway edge, thereby encouraging highspeed turns into the driveway and reducing thedeceleration and interference with the throughtraffic on the major road. This is particularlyimportant for high volume driveways.Figure 3.2.9.5 provides guidelines for limitingthe grade change at the road edge. For highvolume driveways on arterial roads, amaximum grade change of 3% is acceptable.

Table 3.2.9.3 Suggested Minimum Clear Throat Lengths for Major Driveways7

For low volume driveways on local roads, amaximum of 8% is acceptable.

Driveways are constructed at an incline fromthe roadway in order to prevent surfacedrainage along the roadway from dischargingdown a driveway and onto private property.Where this is impractical, curb drainage acrossthe driveway can be effectively controlled byusing a slightly deeper gutter and adjacent catchbasins. It is also common practice to limit theamount of property drainage that drains ontothe roadway via the driveway by providingseparate on-site drainage systems.

Assuming a normal roadway cross-slope of2.0% and the desirable maximum gradechanges defined above, the resulting maximumdriveway grades within the boulevard and

Notes: 1. Refer to Figure 3.2.5.2 for method of measurement.2. For major developments, it is desirable to determine throat lengths and queue

on the basis of a site-specific traffic study.

Land Use Development Size Minimum Clear Throat Length (m) Collector Arterial

Light industrial <10 000 m2 10 000 – 45 000 m2

>45 000 m2

8 15 15

15 30 60

Discount store >3 000 m2 8 8

15 25

Shopping centre <25 000 m2 25 000 – 45 000 m2 45 001 – 70 000 m2

>70 000 m2

8 15 25 40

15 25 60 75

Supermarket <2 000 m2 >2 000 m2

15 25

25 40

Apartments <100 units 100 – 200 units

>200 units

8 15 25

15 25 40

Quality restaurant <1 500 m2 >1 500 m2

8 8

15 25

Fast food restaurant <200 m2 >200 m2

8 15

25 30

General office <5 000 m2 5 000 – 10 000 m2 10 001 – 20 000 m2 20 001 – 45 000 m2

>45 000 m2

8 8

15 30 40

15 25 30 45 75

Motel <150 rooms >150 rooms

8 8

25 30



3.3.3 OUTDOORPEDESTRIANRAMPS, STAIRSAND HANDRAILS

Model requirements for outdoor pedestrianramps, stairs and handrails are provided in theNational Building Code,2 as prepared byNational Research Council Canada. Regulatoryrequirements are the responsibility of eachprovince and territorial government and mayvary from the National Building Code. Provincialand municipal regulations may supplement orreplace the National Building Code guidelines.It is therefore advisable for the designer to beknowledgeable of the local requirements.

Pedestrian travel can be accommodated alonga significant slope using one of three methods:

• a ramp or inclined sidewalk

• a series of steps or stairs

• a combination of ramps and steps

Ramps having a maximum slope of 12:1(8.33%) and appropriate level landings can beeasily negotiated by most pedestrians andpersons in wheelchairs. For barrier-free travelby persons in wheelchairs,3 sidewalks with anincline greater than 20:1 (5.0%) are typicallydesigned as ramps with landings. Ramps areprovided with a level landing area at least 1.2 mlong at intervals of not more than 9.0 m alongtheir length, and where there is an abruptchange in ramp direction. For barrier-freeramps, a minimum length of 1.5 m is usuallyprovided for the landing area. Exterior rampsare normally a minimum of 1.1 m in width, or1.5 m in width where space is required for twowheelchairs to pass, and are constructed ofmaterials that provide a slip-resistant,continuous and even surface. Ramps areparticularly well suited to serving large crowdsof people. It is not always feasible to providesidewalk grades suitable for barrier-free travel,such as where street grades exceed 5.0%. Inthese cases, it is desirable to provide analternate suitable route, if possible.

Stairs are effective in traversing significantvertical heights within a minimum horizontaldistance. Flexibility in stair design permitsadjustments to suit varying site constraints.Stairs, however, present a barrier to personsusing wheelchairs, people pushing strollers orbuggies, and cyclists. The elderly and peoplewith walking impairments may also be severelyrestricted by any appreciable height of stairs.Stairs slow normal pedestrian travel speeds byup to 30% and represent a hazard for largecrowds.

It is desirable to provide stairs at a constantgrade, with uniform run and rise dimensions,through the length of the stairway. Alternateroutes are normally provided for persons withwheelchairs or walking impairments. Stairwaystypically have three or more risers to ensurevisibility to the pedestrian and to prevent trippingoccurrences associated with unexpected singlesteps. Stairs with open risers or nosings aregenerally avoided to prevent possible problemswith toe snagging. Overhead lighting placed toone side and at the top of a stairway is usuallyeffective in illuminating the edge of each treadat night.

The minimum width of a stairway is normally1.1 m. The maximum vertical rise withoutprovision of a landing is normally 3.7 m. Wherelandings are provided, each landing is typicallyas wide as the stairway with a minimum lengthof 1.1 m. If awnings or other shelters areprovided above the stairway, the minimumvertical clearance provided is usually 2.05 m.

Stair runs are normally not less than 230 mmand not more than 355 mm, exclusive ofnosings. Risers are typically not less than125 mm and not more than 200 mm. A 355 mmrun combined with a 150 mm riser allowsrelatively steep slope to be traversed whileaffording a comfortably wide run. For barrier-free design, stair runs of 280 mm minimum andrisers of 180 mm maximum are usuallyprovided. The front edge of the stair treads areoriented at right angles to the direction of travelfor pedestrian safety. Runs and landings areprovided with a slip-resistant finish or areprovided with slip-resistant strips protruding notmore than 1 mm above the surface of each

Streetscaping


tread. A slope of 1% toward the forward edgeof each run is desirable to assure drainage.

Where ramps or stairways are 1.1 m or morein width, it is advantageous to provide handrailson both sides. In cases where ramps orstairways are more than 2.2 m in width,intermediate handrails are desirable and arenormally positioned to ensure that not more than1.65 m exists between adjacent handrails.

Handrail heights are normally in the range of800 mm to 920 mm, as measured vertically froma line drawn along the outer edge of the stairtreads or the surface of the ramp. At least one

of the handrails is normally continuousthroughout the length of the stairway or rampincluding landings. It is also typical to extend atleast one of the handrails 300 mm to450 mm beyond the top and bottom of thestairway or ramp.

Where stairways are provided within a streetright-of-way, it may also be desirable to providea parallel ramp to allow bicycles and strollersto be pushed up immediately adjacent to thestairs.

Figure 3.3.3.1 portrays a number of the designelements pertinent to stairways.1



agency normally has specific clearancerequirements which are to be honoured. Inmany cases, it is desirable to relocate theoverhead utility underground to avoid theconflict, while improving the aesthetics of thestreet right of way.

With respect to street lights, it is desirable toexamine the blocking effect of the future maturetree canopies on the illumination levels intendedfor the roadway and the pedestrian areas.Strategic spacing, consideration of tree canopyform, and pruning of trees relative to theluminaries is often sufficient to avoid significantproblems for the roadway illumination. It isdesirable to position trees midway betweenstreetlight poles and to prune the lower branchesso that unobstructed light reaches a point aminimum of 1.8 m above the mid-span pointsas illustrated on Figure 3.3.4.1.4 It is alsodesirable to select trees with thin, permeablecanopies to reduce the needs of pruning.Separate pedestrian style lighting may berequired to provide the levels of illuminancenecessary for the safety and security of thepedestrian area.

For the climatic conditions in most Canadianurban centres, it is important not to provide adense tree cover adjacent to pedestrian areas.The warmth provided by the sun is generallybeneficial for pedestrian comfort in temperateclimates. The strategic placement of deciduoustrees is effective in providing shade protectionduring hot summer afternoons while allowingthe sun to provide warmth during winter months.

Tree spacing and location are dependent on avariety of factors including:

• desired visual affect

• species of tree

• physical constraints, such as utilities,lighting, and underground structures

• vehicle/vehicle and vehicle/pedestrian sightline requirements

Each streetscaping project is normallyassessed on the basis of the existing conditionsand constraints toward identifying the mosteffective planting plan.

Tree grates are normally provided for trees plantedwithin a hard surfaced pedestrian area. Their usemaximizes the available pedestrian travel spacewhile allowing proper gas exchange at the air/soil contact zone. Tree grates are typicallymanufactured using durable concrete or cast-ironmaterials. It is important to provide surfacedrainage away from the tree trunk to assist inminimizing the intrusion of roadway salt and otherharmful materials into the soil and root system.Raised curbs around each tree pit may beeffective in limiting salt intrusion but are morerestrictive to pedestrian travel than grates whichare flush with adjacent sidewalks. Tree or othergrates not flush with the sidewalk or withopenings greater than 13 mm in diameter maypose a hazard for persons with reduced mobility,and are normally located laterally beyond theline of travel and clear sidewalk width.

Appropriate vegetation can be selected for useon embankment and cut slopes to effectivelycreate soft aesthetics, reduce maintenance andincrease slope stability.

3.3.4.3 Vehicular TrafficConsiderations

The location and configuration of vegetation aredetermined so as to maintain the sight linesrequired at street intersections and otherpedestrian crossing areas. Sight distancerequirements are discussed in Chapter 2.3 −Intersections. Shrubs less than 1.0 m in heightand trees with canopies providing at least 2.4 mof vertical clearance may be considered withinan intersection sight triangle. Hedges, highshrubs and coniferous trees which block sightlines are avoided in these critical areas.Generally, it is desirable to eliminate, or at leastrestrict, the type and amount of vegetation withinthe critical sight triangles at intersection areasto maintain pedestrian and vehicular safety.

The locations of traffic signs, particularlyregulatory and warning signs, and traffic signalsare normally co-ordinated with the plantinglayout. Vegetation at locations that may blockthe driver’s view of traffic signs and signals areavoided.

When creating a tree planting plan, consultationwith the adjacent property owners and business

Streetscaping


operators is desirable. It may be desirable notto block important or interesting buildings fromthe view of the passing vehicular traffic. Certainbuildings may be equally or more important tothe visual quality and character of the street thanplanted vegetation.

Trees with trunk diameters greater than 150 mmat maturity are considered fixed objects. Groupsof small trees or shrubs closely spaced mayhave the same effect as a single large tree.Therefore, for larger trees and tree groups, it isadvisable to locate trees in accordance with theclear zone guidelines, based on design speed,from the edge of the travel lane (existing orfuture) to the tree trunk, as outlined in Chapter3.1. Permitted locations for trees are often amatter of local policy, but it is generally desirableto avoid having large trees in close proximity ofvehicular travel lanes, such as within boulevardsless than 2.0 m and medians less than 4.5 m inwidth. When parking is provided along an urbanstreet where streetscaping is employed, theparking area generally provides a suitable bufferbetween the traffic lanes and the boulevardtrees and other fixed objects, and therefore thecurb to fixed object dimension is less critical.

A minimum setback of 750 mm from the curbface to the tree trunk face is generally desirablein all cases. This provides a suitable minimumclearance for passengers to open a vehicle doorand exit/enter reasonably unimpeded, reducesthe frequency of splashed salt and other harmfulmaterials onto the tree trunk and minimizes theintrusion of root growth into the road subgrade.

3.3.4.4 Roadside Treatments

The selection of the most appropriate roadsidearea treatments is influenced by a number offactors including:

• the total curb to property line (roadside)width available

• the clear sidewalk width required toaccommodate the anticipated pedestriancharacteristics and volumes

• the nature and characteristics of theadjacent land use

• the volume, speed and type of vehiculartraffic along the adjacent roadway

• the location of overhead and undergroundutilities

Generally, four options are available to thedesigner as illustrated in Figure 3.3.4.2.5 Eachlandscaping project is assessed on its individualcharacteristics. It may be advantageous oncertain projects to implement combinations ofoptions to suit varying land uses, vehicular trafficand parking conditions, and the physicalconstraints; combination of options may bemore visually stimulating in making themotorists more aware of the drivingenvironment and thus enhancing safety. Wherea change is made from one option to another, itis important to design the pedestrian routetransitions to be obvious and unobstructed.

A description and typical application of the fouroptions are outlined by the following:

Option A – Boulevard and Border VerticalFeatures

This treatment is particularly beneficial wherewide expanses of paved areas exist on eitherside of the roadside. An example is a pedestrianarea between a multi-lane road and a parkingarea for a regional shopping centre. The verticalfeatures and the created enclosure effectivelybuffer the pedestrian from both the busy roadand the adjacent land use. To provide anappropriate pedestrian scale, the ratio ofpedestrian area width to height of the verticalfeatures is normally in the range of 1:1 to 1:2.

Option B – Border Vertical Features Only

With this option, a buffer is introduced onlybetween the pedestrian area and the adjacentdevelopment and therefore provides a physicalseparation between the pedestrian area and theadjacent land uses. Common applications arealong off-street parking areas and adjacent toindustrial land uses, where large and unsightlyareas are visible to the pedestrian. Theaesthetics of residential land uses may also beimproved by this style of treatment. Thisarrangement may also be the only feasible optionwhere overhead utility lines exist along the



3.4.5 ALIGNMENTELEMENTS

The alignment elements in the followingparagraphs are generally applicable to bikepaths. Other classifications of bikeways aredesigned for motor vehicle traffic and thosestandards are adequate for bicycles, with theexception of stopping sight distance. Stoppingsight distance is greater for bicycles than motorvehicles, particularly in the case of steepdowngrades, and should be considered in thedesignation of bike lanes and bike routes.

3.4.5.1 General Approach

As for any transportation facility, there is aresponsibility to generate a collision free design.The standards and practices for bikeways thatfollow are intended to assist designers to meetthis responsibility. However, the bicycle is adistinct vehicle which is often used in locationsof substandard geometrics. In such cases,providing suitable warning signs along bikewaysis a significant consideration in maintainingsafety.

3.4.5.2 Design Vehicles

The suggested dimensions of a bicycle to beused in the design of bikeways are:

• length, 1.75 m

• width at pedals, 400 mm

• height to lowest pedal position, 100 mm

• width at handlebars, 800 mm

• height to handlebars, 1.25 m

• height to top of seated riders, 2.0 m

Desirable bikeway widths for design are asfollows:

• one-way, 1.20 m to 1.60 m

• two-way, 2.20 m to 2.60 m

3.4.5.3 Design Speed

The speed at which a cyclist travels is dependenton several factors, including the type andcondition of the bicycle, the purpose of the trip,the condition and location of the path, the speedand direction of the wind, and the physicalcondition of the cyclist. Paved bike paths aredesigned for a selected speed that is at leastas high as the preferred speed of the fastercyclists. In general, a minimum design speedof 30 km/h is used; however, when thedowngrade exceeds 4%, or if strong tailwindsprevail, a design speed of 50 km/h is advisable.

On unpaved paths, where cyclists tend to ridemore slowly, a lower design speed of 25 km/hcan be used or where the grades or theprevailing winds dictate, a higher design speedof 40 km/h can be used. Since bicycles have ahigher tendency to skid on unpaved surfaces,horizontal curvature design should take intoaccount lower coefficients of friction.

3.4.5.4 Stopping Sight Distance

Minimum stopping sight distance for bicyclesis the distance required to bring a bicycle to acontrolled full stop. It is a function of the cyclists’perception and brake reaction time, the initialspeed of the bicycle, the coefficient of frictionbetween the tires and the bikeway surface andthe braking capability of the bicycle. Thestopping sight distance is given by theexpression:

(3.4.1)

Where: SSD = stopping sight distance (m)

V = design speed (km/h)

f = coefficient of friction

G = grade (% up grade is positiveand down grade is negative)

The expression is based on a perception-reactiontime of 2.5 s. Table 3.4.5.1 illustrates minimumstopping sight distance for a range of speedsfrom 10 to 50 km/h and grades up to 12%. For

)100/gf(255

VV694.0SSD

2

++=

Bikeways


two-way facilities, the values for the descendingdirection control the design. Coefficient of friction(f) is taken to be 0.25 for paved surfaces, which

accounts for the poor wet weather brakingcharacteristics of many bicycles.2

Table 3.4.5.1 Minimum Stopping Sight Distance for Bicycles(Paved Surface, Wet Conditions)

3.4.5.5 Horizontal Alignment

Radius and Superelevation

The minimum radius of a circular curve for abikeway is a function of bicycle speed,superelevation, and coefficient of friction. Thesevariables are related by the expression:

(3.4.2)

Where: R = radius (m)

V = design speed (km/h)

e = superelevation (m/m)

f = coefficient of lateral friction

This relationship is used to determine theminimum design radius for given designspeeds. For most applications and conditions,the superelevation rate will range from aminimum of 0.02 to 0.05 m/m. The coefficientof lateral friction used for design of pavedbikeways varies from 0.3 at 25 km/h to 0.22 at50 km/h. For the design of unpaved surfaces,lateral friction factors are reduced to 50% ofthose of paved surfaces. Table 3.4.5.2 givescoefficient of lateral friction and minimum radiusfor a range of design speeds based onsuperelevation rates of 0.02 and 0.05 m/m.

Where curve radii less than those inTable 3.4.5.2 are used, or superelevation isunavailable, warning signs in advance of thecurve are appropriate.

Lateral Clearance on Horizontal Curves

Lateral clearance to obstructions on the insideof horizontal curves is based on the need to

)fe(127

VR

2

+=

Minimum Stopping Sight Distance (m)Design Speed (km/h)Grade

(%) 10 15 20 25 30 35 40 45 50121086420-2-4-6-8-10-12

888888999991010

13131313131414141515161617

18181919192020212122232426

-242525262627282930323436

--

3232333435363839424448

---

40414244454750535361

----

495153555861657076

-----

6163666973688492

------

7477818692100110

Notes: For the purposes of measuring stopping sight distance the height of eye is normally taken to be1.37 m and the height of object zero, to provide for impediments to bicycles at pavement level,such as potholes.For selection of design speed, refer to Subsection 3.4.5.3.



provide sufficient sight distance to an object onthe intended path of the bicycle for which therider has a need to stop. The line of sight to theobject is taken to the corner of the visualobstruction, and the stopping distance ismeasured along the intended path, which istaken to be the inside edge of the inner lane.

Figure 3.4.5.1 illustrates the method ofmeasurement and gives a mathematicalexpression for the calculation of lateralclearance. Table 3.4.5.3 gives the lateralclearance for a range of radii from 10 to 80 mand stopping sight distances from 10 to 100 m.

Table 3.4.5.2 Minimum Radii for Paved Bikeways

Figure 3.4.5.1 Lateral Clearance for Stopping Sight Distance

Design Speed(km/h)

Coefficient of LateralFriction

Minimum Radius for Design (m)

e = 0.02 m/m e = 0.05 m/m253035404550

0.300.280.270.250.230.22

152433476482

142130425773

Bikeways


The lateral clearance values shown occur at themid point of the curve.

3.4.5.6 Vertical Alignment

Grades

Grades greater than 5% are normally avoidedon bikeways. Where there are compellingreasons for exceeding 5%, the length is keptas short as possible and higher design speedsare desirable to accommodate higher speedsin the downhill direction. On long steepupgrades it is desirable to have a relatively flatarea of grade, in the order of less than 3%, every100 m for rest. Where new bike path isproposed, it is preferable to make the routelonger to maintain lower grades, than shorterwith higher grades.

The normal minimum longitudinal gradient forbikeways is 0.6%. Where surface drainage isprovided by adequate cross-slope and lateralslope of the ground away from the bikeway, theminimum grade may be zero.

Crest Curves

The minimum length for crest curves is basedon providing at least minimum stopping sight

distance (S), as described in Subsection 3.4.5.4.The eye height is taken to be 1.37 m and theobject height is taken to be zero, based on theability to see a fault in the bike path surfacesufficiently soon to be able to stop. Where designis predicated on a significant usage by children,a lower eye height may be appropriate.Table 3.4.5.4 gives minimum lengths for designspeeds up to 50 km/h and algebraic differencesin grade (A) up to 25%. If lengths are requiredfor intermediate values, the table may beinterpolated or the formula used. Stopping sightdistance is based on level grade. Where thereis a significant difference in approach anddeparture grades, adjustment to the length ofcurve to account for significant grade differencesmay be appropriate, based on the values inTable 3.4.5.1.

Sag Curves

Where bike paths are used in the hours ofdarkness, they are normally, for securityreasons, illuminated. There is little need to applysag curves sufficiently flat to provide sightdistance by headlight as for motorized vehiclesin non-illuminated areas. The criterion forbicycles, therefore, is comfort. The sag curve

Table 3.4.5.3 Lateral Clearance for Bicycles on Horizontal Curves

Clearance (m)Stopping Sight Distance (m)Radius

(m) 10 20 30 40 50 60 70 80 90 100101520253035404550556065707580

1.20.80.60.50.40.40.30.30.20.20.20.20.20.20.2

4.63.22.42.01.71.41.21.11.00.90.80.80.70.70.6

9.36.95.44.43.73.22.82.52.22.01.91.71.61.51.4

-11.59.27.66.45.64.94.43.93.63.33.12.82.72.5

--

13.711.59.88.67.66.86.15.65.14.74.44.13.9

--

18.615.913.812.110.79.68.78.07.36.86.35.95.6

---

20.818.216.114.412.911.810.89.99.28.28.07.5

----

22.920.518.416.615.213.912.811.911.110.49.8

----

27.925.222.820.718.917.416.115.014.013.110.8

-----

30.027.425.023.021.219.718.317.116.115.1

Note: No value is shown where deflection angle exceeds 180° (stopping sight distance > R).



These inexperienced cyclists have the option ofmaking a two-legged left turn by riding a coursesimilar to that followed by a pedestrian, ordismounting from their bicycles and walkingthem across the crosswalks (Figure 3.4.7.3).

3.4.7.5 Bikeway Ramps

At the intersection of bike paths and roadways,bikeway ramps are typically installed to facilitatemovement between the two. Where thepotential for conflict between bicycles and motorvehicle traffic is high, consideration is given toappropriate signs warning drivers and cyclistsof the conflict area.

Configurations for a typical corner layout and atypical mid-block layout are shown inFigure 3.4.7.6. Alternatives to ramps at bikepath / roadway intersections include raisedcrosswalks and platform intersections, whichfavour the cyclist over the motor vehicle.

3.4.7.6 Bikeways CrossingFreeway InterchangeRamps

Background

Motorized traffic on interchange ramps tend tooperate at fairly high free flow speeds; this tendsto increase the risk of more severe collisions. Itis critical to provide good visibility andmanoeuvring space to allow cyclists andmotorists to function / interface effectively andsafely. It is therefore desirable to accomplishcrossings in the shortest distance feasible,utilizing the highest intersecting angle feasible.

The following sections discuss recommendedat-grade crossings; however, grade separationdesigns utilizing a bicycle path could be used ifthe approach ramp elevations are appropriate,and if bicycle volumes are fairly high and motortraffic volumes are high. Standard bicycle pathgeometric guidelines would be applied to theapproaches to a grade separated crossing fora bikeway.

Width and Layout

It is desirable to control the location of cyclistsin an interchange area on a crossing roadway

by utilizing a separate shoulder / bike lane inorder to regulate cyclists crossing aninterchange ramp, and thus ensure cyclists andmotorists each know what to expect of oneanother. Since manoeuvring space is also acritical factor in reducing the risk of collisions, itis necessary to provide at least a 1.5 metre widebikeway for each direction of travel within theinterchange limits.

Cyclists should yield to motor vehicle traffic,hence, a bike yield sign should be erected tocontrol cyclists; a fairly tight design radius maybe used since cyclists should slow and yield atramp crossings.

Freeway / Expressway Exit (Crossing RoadwayEntrance) Type Ramps (Figure 3.4.7.7)

The freeway exit type ramp represents a lesshazardous crossing than the freeway entrancetype ramp; cyclists can see car / truck traffic,which the cyclist must manoeuvre through, onthe freeway exit ramp entering a crossingroadway. As a result, a fairly tight turning radiusdesign for the bikeway can be accepted.

The minimum recommended designparameters are displayed in Figure 3.4.7.7.

Freeway / Expressway Entrance (CrossingRoadway Exit) Type Ramps (Figure 3.4.7.8)

The freeway entrance type ramp is potentiallymore dangerous than the exit type ramp;cyclists must look over their shoulder toestablish the presence of oncoming motorvehicle traffic in order to weave across a ramplane. It is necessary to guide cyclists to intersectthe ramp at an angle which will encourage themto slow and check behind, with adequatedistance from the crossing, for vehicles. Thecyclists can then establish whether there areany turning cars which may necessitate caution/ stopping, or whether the way is clear and theycan proceed across the ramp. In order toprovide an adequate operating intersectionangle, and adequate stopping distance, thecyclists should be guided away from the rampand then back toward the ramp at an acceptablecrossing angle. The design configurationappears in Figure 3.4.7.8 with dimension detailsgiven in Table 3.4.7.2.

Bikeways


Figure 3.4.7.6 Typical Bikeway Ramps



Figure 3.5.2.1 Minimum Bus Bay Dimensions

For an articulated bus, a bus bay length of 25 m and 30 m tapers are suggested minimum dimensions.

Pullouts


Figure 3.5.2.2 Typical Island Type Bus Bay

3.1.2 EXPLICIT ANALYSIS OF ROADSIDE SAFETY FEATURES · Roadside Safety Page 3.1.2.2 December 2009...

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