Ashley River Bridge Traffic Study€¦ · Appendix A. 2015 Ashley River Bridge Traffic Study Update...

Ashley River Bridge Traffic Study Lane Closure Re-Evaluation

Charleston County Transportation Development

Charleston, SC August 2017


August 2017 | i

Contents

Executive Summary ...................................................................................................................................... 3

1 Project Overview ................................................................................................................................. 6

2 Traffic Data .......................................................................................................................................... 6

2.1 Traffic Volumes and Patterns .................................................................................................... 6

2.2 Travel Time Data ....................................................................................................................... 7

3 VISSIM Analysis .................................................................................................................................. 7

3.1 Measures of Effectiveness ........................................................................................................ 7

3.2 Calibration of Existing Condition (2016) Simulation Model ....................................................... 8

3.3 2016 Analysis Results ............................................................................................................... 9

3.4 Future Traffic Forecast ............................................................................................................ 13

3.5 2028 Analysis Results ............................................................................................................. 13

3.6 Expected Year of Failure ......................................................................................................... 16

4 Summary ........................................................................................................................................... 17

Tables

Table 1. HCM-Derived Composite Density LOS Thresholds ........................................................................ 8 Table 2. Existing Condition (2016) Model – Travel Time Calibration ........................................................... 9 Table 3. Existing Condition (2016) Model - Volume Calibration ................................................................... 9 Table 4. 2016 Link Density .......................................................................................................................... 10 Table 5. 2016 No Build and Build Intersection Operations ......................................................................... 13 Table 6. 2028 Level of Service ................................................................................................................... 14 Table 7. Future Conditions (2028) Intersection Operations ........................................................................ 15

Figures

Figure 1. VISSIM Link ID ............................................................................................................................. 11 Figure 2. 2016 No Build and Build Average Travel Time Results............................................................... 12 Figure 3. Future Conditions (2028) Average Travel Time Results ............................................................. 15 Figure 4. Average Build Density over Time ................................................................................................ 16

Appendices

Appendix A. 2015 Ashley River Bridge Traffic Study Update

Appendix B. Model Calibration

Appendix C. Signal Timings

Appendix D. Existing Conditions (2016) Analysis

Appendix E. Future Conditions (2028) Analysis


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Executive Summary The four-lane T. Allen Legare Bridge on Northbound US 17 provides one of only two connections across the Ashley River from the West Ashley community into downtown Charleston, SC. This bridge has been the topic of several studies to determine if it can be modified to safely accommodate bicycle and pedestrian traffic, including traffic studies in 2011 and 2015 that evaluated the potential impacts of eliminating one travel lane on the bridge and its immediate approach in order to accommodate a barrier-separated two-way shared-use path in the space currently used as the fourth travel lane. An additional study was completed in 2016 that evaluated the performance of the tests on the two proposed lane configurations performed in April and May of 2016.

The study summarized in this report provides an update to the traffic analysis completed in 2015, and analyzes traffic count data collected in 2016, as well as travel time data collected in conjunction with the 2016 study. The intent is to evaluate the operations of the proposed improvements with 2016 traffic as well as in 2028, which correlates to a 10 year outlook horizon from the implementation of the proposed improvements.

Evaluation Methodology

The evaluation has been completed through the use of the traffic engineering software VISSIM, which simulates the traffic operations of the area on the approach to the bridge, where Folly Road, US 17, and SC 61 merge together to create the existing four lane section. The VISSIM simulation is used due to the complex roadway and ramp configuration in the study area which has twelve possible origin-destination pairs and nine separate weaving sections.

Analysis Results

The VISSIM simulation results for 2016 show increases in travel times for each origin roadway through the study area in the Build condition. Section 2.2 of the report shows the limits of the travel time runs. The analysis shows travel time increases on Folly Road due to the merge condition / lane drop; the average travel time on Folly Road (east of Wesley Drive) is expected to increase from 2.00 minutes to 2.95 minutes (an increase of 57 seconds or 47%) in the Build condition. US 17 showed an increase in from 1.72 minutes in the No Build scenario to 2.10 minutes in the Build scenario (an increase of 22 seconds or 21%). Additionally, SC 61 increased from 1.72 to 1.92 minutes between the No Build and Build scenarios (an increase of 11.6 seconds or 11%).

As previously stated in the 2015 Traffic Study (Appendix A), it is common traffic engineering practice to strive to achieve at least level of service (LOS) E on urban roadways during the AM and PM peak hours. In the study area, the most accurate metric for LOS is vehicle density (vehicles per mile per lane). The overall average vehicle density results in acceptable levels of service for both the 2016 No Build (LOS C) and 2016 Build (LOS E) conditions. The change in LOS for the Build condition is not unexpected since the removal of one lane will have a direct effect on the overall average density of the study area. Additionally, individual segments along


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the corridor saw increases in density between the No Build to Build conditions that resulted in failing conditions (>45 veh/mi/ln). Folly Road (east of Albemarle Road) and the bridge segment itself rose from LOS C in the No Build scenario to LOS F in the Build scenario due to the new merge conditions. Segments along US 17 and SC 61 saw higher densities as well but did not see a decrease in LOS.

There were no modeled changes to traffic operations at intersections in the West Ashley area in 2016 due to the Build condition, with the exception of minor changes in delay at the Folly Road / Albemarle Road intersection. These changes at this intersection resulted in a change in the overall intersection LOS from LOS A to LOS B.

The VISSIM simulation results for 2028 showed the average travel time on Folly Road from Wesley Drive to the east is projected to increase from 2.22 minutes to 4.44 minutes (representing an increase of approximately 133 seconds). SC 61 showed an increase from 1.78 minutes to 2.33 minutes (an increase of 34 seconds or 31%). US 17 showed an increase in travel time from 1.80 minutes to 3.22 minutes (an increase of 85 seconds or 78.8%).

The overall average vehicle density (vehicles per mile per lane) in 2028 results in acceptable operations at LOS D (32.8 veh/mi/ln) for the No Build condition. The Build condition is expected to fall below acceptable operations at LOS F (58.6 veh/mi/ln). The ramp from Folly Road saw the largest changes in density along the corridor. The model indicated that the ramp was LOS D in the No Build condition but doubled the density in the Build condition which resulted in LOS F conditions. Additionally, a majority of segments along US 17 experienced failing conditions in the Build scenario where only one segment experienced failing conditions in the No Build scenario. The segments that make up the bridge saw decreased performance from LOS D in the No Build to LOS F in Build. See Table 6 in the report for further detail.

Intersections in the West Ashley area are not expected to be impacted in 2028 Build condition, with the exception of changes at the Folly Road / Albemarle Road intersection as well as the Bee Street / Lockwood Drive intersection. While delay at the Folly Road / Albemarle Road intersection is shown to increase due to the Build configuration related to the downstream merge / lane drop condition, the intersection is shown to still operate acceptably at LOS C overall. The Bee Street / Lockwood Drive intersection is expected to have increased delay which will result in a change of LOS from LOS C to LOS D.

The results of the density analysis for the 2016 and 2028 Build scenarios were used to develop an expected year of failure for the overall bridge study area. To determine the year of failure, an interpolation was performed between the overall merge area densities for the 2016 and 2028 Build scenarios. Using the interpolation, it was determined that failing conditions along the bridge could be expected by 2017.


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A qualitative analysis was performed on the roadway model to determine how effective the predicted mode shift would have to be to maintain the results from the 2016 Build analysis in 2028. It is assumed that if the volumes along the bridge remain the same in 2028 as in 2016, the simulated results observed in the 2016 Build scenario would be the same results observed in 2028. To maintain the same volume, the 411 additional vehicles being added over the next 12 years would have to be shifted to other modes of transportation to get across the bridge. At an average assumed rate of 1.2 persons per vehicle, this would result in a need of 493 people using other transportation modes including biking or walking along the new path during the AM peak hour in 2028.

Summary

This study has evaluated the traffic operational impacts that would occur if one travel lane were removed from the Northbound US 17 Bridge over the Ashley River and its approach in order to accommodate a barrier-separated two-way shared use path in the space currently used by the fourth travel lane. This study is an update of the previous 2015 traffic study to incorporate data collected in 2016. A VISSIM traffic simulation model was calibrated to the 2016 travel time and volumes on the four-lane section and used to evaluate the operational changes that are projected to occur with the conversion of the bridge and its approach to a three-lane section.

The traffic study update indicates the intersections in the surrounding areas would experience increases in delay but would not experience any change in LOS from the lane reduction on the bridge. The roadway density in the bridge area indicates the roadway is expected to experience failing traffic conditions in the 2028 Build scenario while also experiencing on average a 75% increase in travel time over the 2028 No Build scenario for all roadways in the study area.


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1 Project Overview The four-lane T. Allen Legare Bridge on Northbound US 17 provides one of only two connections across the Ashley River from the West Ashley community into downtown Charleston, SC. This bridge has been the topic of several studies to determine if it can be modified to safely accommodate bicycle and pedestrian traffic, including traffic studies in 2011 and 2015 that evaluated the potential impacts of eliminating one travel lane on the bridge and its immediate approach in order to accommodate a barrier-separated two-way shared-use path in the space currently used as the fourth travel lane. An additional study was completed in 2016 that evaluated the performance of the tests on the two proposed lane configurations performed in April and May of 2016.

The lane closure tests performed in April and May of 2016 indicated inconsistent travel times in comparison to the VISSIM model’s predicted travel time changes. Charleston County requested HDR re-evaluate the microsimulation model to include the 2016 volume and travel time data collected before and during these field tests. This study provides a summary of the results from the re-evaluation of the updated microsimulation model.

The traffic data was collected to answer the following questions:

How do the travel times from the microsimulation compare to travel time results from the 2016 lane closure tests?

What operational changes should be expected between the existing lane geometry scenario and the proposed three-lane section on the bridge scenario?

When is the bridge expected to reach conditions considered to be failing?

2 Traffic Data

2.1 Traffic Volumes and Patterns In the 2016 study, 72-hour traffic volume counts were collected at six locations in the study area including the three roadways approaching the bridge, mainline Northbound US 17, and the off-ramp at Lockwood Drive/Bee Street. Additionally, peak hour turning movement counts were collected at the intersection of Folly Road at Maybank Highway. These volumes were combined with those collected in the 2015 study to develop an existing volume set for the area. The counts were grown from the year they were collected to a base year of 2016 using a growth rate of 1.3% based on the changes seen in the volumes collected on the bridge. The previous report can be found in Appendix A.


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2.2 Travel Time Data An additional set of traffic data collected was travel time runs during the 7:00 AM to 9:00 AM peak period. The runs were conducted either using a GPS logger that recorded data at one second intervals including time, speed and position, or using a stopwatch and recording times at key points along the study corridor. Travel time runs were collected for a total of nine origin-destination (O-D) pairs, as follows:

1. SC 61 (at Wesley Drive) to Northbound US 17 at Lockwood Drive Off-Ramp

2. SC 61 (at Wesley Drive) to Northbound Lockwood Drive/Eastbound Bee Street

3. SC 61 (at Wesley Drive) to Southbound Lockwood Drive

4. US 17 (at Wesley Drive) to Northbound US 17 at Lockwood Drive Off-Ramp

5. US 17 (at Wesley Drive) to Northbound Lockwood Drive/Eastbound Bee Street

6. US 17 (at Wesley Drive) to Southbound Lockwood Drive

7. Folly Road (at Wesley Drive) to Northbound US 17 at Lockwood Drive Off-Ramp

8. Folly Road (at Wesley Drive) to Northbound Lockwood Drive/Eastbound Bee Street

9. Folly Road (at Wesley Drive) to Southbound Lockwood Drive

Travel time runs were collected before a field test of the proposed lane closure condition on March 24, 2016. The travel time runs for the modified lane merge condition in Test #2 were conducted on May 11, 2016.

3 VISSIM Analysis The evaluation of the removal of one travel lane on the Northbound US 17 Bridge and its approach in order to accommodate a barrier-separated shared use path was completed using the traffic simulation software, VISSIM. VISSIM is a microsimulation software that is widely used across the country to evaluate traffic operations within complex geometric configurations. VISSIM was previously used to evaluate the traffic operations in the West Ashley community as part of the US 17/SC 61 Improvements Project and was used for the Ashley River Bridge Traffic Study in 2011 and 2015. VISSIM allows the impacts of downstream disturbances and capacity issues to propagate back through the model; therefore, the traffic operation within each individual segment is influenced by the operations in adjacent segments and the study area as a whole. In contrast, the methods used in the Highway Capacity Manual (HCM) only look at isolated locations and do not fully account for queue spillback in an analysis.

3.1 Measures of Effectiveness The Measures of Effectiveness (MOE) that will be used in this project include travel time, density (vehicles per mile per lane), and level of service (LOS). As the density and LOS rise due to the reduction of a travel lane, the travel time through the corridor may not change significantly. Due to this, the travel time is considered the critical MOE for this project.


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It is common traffic engineering practice to strive to achieve at least LOS E on urban roadways during the peak hours. To determine an overall LOS for the entire study area, an average of the LOS thresholds for density was computed from the thresholds in the 2010 HCM for various facility types including multilane highway basic sections, multilane highway weaving sections, and ramp junctions (merge/diverge areas). This approach is used because the section in question is complex and cannot be defined by any one facility type. The average of thresholds from multiple facility types results in a single set of LOS values, which are shown in Table 1. The VISSIM simulation reports a density, volume and speed for each link segment by lane. Using weighted averages based on link volume, a weighted average density can be developed for each alternative.

Table 1. HCM-Derived Composite Density LOS Thresholds

LOS Multilane Highway

(veh/mi/ln) Multilane Highway Weaving

(veh/mi/ln) Ramp Junction

(veh/mi/ln) Average

(veh/mi/ln)

A 11 12 10 11.0

B 18 24 20 20.7

C 26 32 28 28.7

D 35 36 35 35.3

E 45 a a 45.0

Source: Transportation Research Board (TRB) Highway Capacity Manual (HCM) 2010. Average values account for multiple facility types across the analysis segment a LOS F is reached when demand exceeds capacity, but no specific density threshold defines that

point.

3.2 Calibration of Existing Condition (2016) Simulation Model Calibration of any simulation model is important to achieving reliable results. The 2016 No Build model was calibrated based on several inputs, most importantly of which is travel time based on the series of travel time runs discussed in Section 2.2. Several other model inputs were adjusted to help calibrate travel time, including desired free flow speed curves designed for each study segment, and driver parameters in merge areas.

The average of the measured existing conditions travel times based on the travel time runs completed for each roadway on the routes previously discussed are summarized in Table 2. The calibration of 2016 existing conditions in the VISSIM model included a comparison of the average results from ten (10) simulation runs to the measured average travel time based on the same route limits. The routes selected were along US 17, SC 61, and Folly Road from Wesley Drive to multiple locations on the east side of the bridge.


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Table 2. Existing Condition (2016) Model – Travel Time Calibration

Roadway Measured Travel

Time (min) VISSIM Travel

Time (min) Difference (sec)

SC 61 2.01 2.25 10.9

US 17 1.86 2.44 30.8

Folly Rd 2.41 2.69 18.0

Weighted Average 2.13 2.49 20.0

To calibrate the volumes, the VISSIM output for the ten runs was compared to the existing 2016 volumes. These volumes represent the total number of vehicles that are recorded in and processed through the simulation network, and are directly comparable to the measured traffic counts. In order to achieve proper calibration, the average VISSIM volumes should be within 15% of the existing volumes.

As shown in Table 3, the average volume for each of the three origin roadways was well within the 15% threshold. With the favorable travel time and volume results, the existing 2016 model is considered calibrated. Detailed analysis of the calibration can be found in Appendix B. The traffic signals coded in the VISSIM model use the existing signal timings provided by the City of Charleston. See Appendix C for the provided signal timings.

Table 3. Existing Condition (2016) Model - Volume Calibration

Roadway Measured Target AM Peak Hour Volume

VISSIM Average AM Peak Hour Volume

% Difference

US 17 1,266 1,251 -1%

SC 61 1,189 1,184 0%

Folly Rd 1,823 1,758 -4%

NB US 17 Bridge 4,278 4,198 -2%

3.3 2016 Analysis Results As discussed in Section 2.2, travel times were one of the metrics used to evaluate the performance of the proposed build design. Travel time results from VISSIM were computed for each roadway based on a weighted average of the travel times between each origin-destination pair (three destination points for each originating roadway). An overall weighted average was also computed across all roadways. The travel times for each originating roadway included the intersection approach at the Bee Street/Lockwood Drive signal to capture the reduced delays and queuing due to the proposed improvements at that location in the Build condition. Also, the travel times for Folly Road began at Wesley Drive which included the segment between Wesley Drive and Albemarle Drive to account for any delays at Albemarle Road due to the lane merging that could occur just downstream from the intersection in the Build condition.


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The results of the VISSIM analysis for the 2016 conditions in Table 4 indicate the overall average vehicle density within the study area results in acceptable levels of service for both the 2016 No Build (LOS C) and Build (LOS E) conditions. Additionally, the analysis indicates Folly Road will experience failing conditions as it approaches US 17 as well as the segments used to analyze the bridge. The change in LOS for the Build condition is not unexpected since the removal of one lane will have a direct effect on the overall average density of the study area. Additionally, US 17 experienced increases in density that did not result in a change of LOS. A map of the VISSIM Link segments is provided in Figure 1 to assist with identifying the density segments in Table 4.

Table 4. 2016 Link Density

VISSIM Link ID Link Description

No Build Existing Build

Average Density (veh/mi/ln) LOS


47 Folly Road 28.3 C 55.3 F

52 Folly Road 27.4 C 55.6 F

48 US 17 37.5 E 44.4 E

50 US 17 36.9 E 38.4 E

74 US 17 25.9 C 27.0 C

73 US 17 26.1 C 26.7 C

41 US 17 21.0 C 21.1 C

4 Merge of US 17 and Folly Road 31.4 D 51.3 F

76 SC 61 37.4 E 38.5 E

72 SC 61 37.1 E 37.5 E

56 SC 61 37.5 E 37.5 E

55 SC 61 38.1 E 37.8 E

45 SC 61 38.6 E 38.3 E

44 SC 61 36.5 E 36.0 E

42 SC 61 24.3 C 24.2 C

7 Merge of US17/Folly Road and SC 61 33.0 D 49.2 F

77 T. Allen Legare Bridge 26.5 C 46.8 F

101 T. Allen Legare Bridge 28.7 C 43.3 E

Weighted Average 28.7 C 44.9 E


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Figure 1. VISSIM Link ID for Link Density Analysis


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As shown in Figure 2, the average travel time for Folly Road traffic is projected to increase by 57 seconds or 47% in the 2016 Build condition compared to the existing condition. US 17 showed an increase from 1.72 minutes in the No Build scenario to 2.10 minutes in the Build scenario (an increase of 22 seconds or 21%). Additionally, SC 61 increased from 1.72 to 1.92 minutes between the No Build and Build scenarios (an increase of 11.6 seconds or 11%). Overall, the average additional travel time across all roadways in the Build condition is estimated at 34 seconds or 31% more than the existing condition. Detailed analysis results for the 2016 conditions analysis are included in Appendix D. In comparison to the average travel time runs from Test 2, there were increases of 14 seconds on SC 61, 40 seconds on US 17, and 60 seconds on Folly Road.

Figure 2. 2016 No Build and Build Average Travel Time Results

It is important to note the Build configuration did not impact the intersection operations at the upstream intersections in the West Ashley area because no volumes, lane configurations, or signal timings are proposed to be changed in this area. The only intersections anticipated to have increases in delay are the Folly Road / Albemarle Road intersection and the Lockwood Drive / Bee Street intersection. The Folly Road approach at the Folly Road / Albemarle Road intersection heading east towards downtown Charleston will have a delay increase to due to the downstream merge required at the lane drop point. Table 5 summarizes the average overall intersection delay and LOS for the existing and Build conditions at the five intersections immediately adjacent to the project. As shown in the table, the intersections studied experienced minimal impacts from the closure of the lane.

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

SC 61 US 17 Folly Rd All Roads

Ave

rage

Tra

vel T

ime

(min

)

Average Travel Time (2016)

No Build

Build

+12 sec / 11% +22 sec / 21%

+57 sec / 47%

+34 sec / 31%


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Table 5. 2016 No Build and Build Intersection Operations

Alternative Primary Road Secondary Road Intersection

Delay (sec/veh) LOS

No Build (Existing)

SC 61 Wesley Drive 23.6 C

US 17 Wesley Drive 49.2 D

Folly Road Wesley Drive 16.4 B

Folly Road Albemarle Road 9.1 A

Lockwood Drive Bee Street 26.1 C

Build

SC 61 Wesley Drive 23.9 C



Folly Road Albemarle Road 18.1 B


3.4 Future Traffic Forecast The forecasted growth rate in the Ashley River area was developed in the 2015 traffic study. Based on the adopted 2015 and 2040 Berkeley Charleston Dorchester Council of Governments (BCDCOG) regional travel demand models, the Ashley River Bridge is projected to see a 0.8% annual growth rate in daily traffic volumes. This growth rate was applied to the existing 2016 traffic volumes to develop 2028 forecasted traffic volumes.

3.5 2028 Analysis Results The results of the VISSIM analysis for the 2028 future conditions in Table 6 indicate the overall average vehicle density in the study area results in acceptable operations of LOS D for the No Build condition and failing operations of LOS F for the Build condition. This result confirms that Build condition traffic operations are forecasted to worsen to a failing level of operation by the year 2028 based on the projected regional growth. Additionally, Folly Road shows an increase in density that resulted in a reduction in operations from LOS D in the No Build condition to LOS F in the Build condition. US 17 also saw a reduction in operations from LOS D and E to LOS F for a majority of segments.


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Table 6. 2028 Level of Service

VISSIM Link ID Link Description

No Build Existing Build



47 Folly Road 30.6 D 66.1 F

52 Folly Road 29.5 D 70.5 F

48 US 17 43.6 E 68.8 F

50 US 17 45.5 F 64.9 F

74 US 17 30.0 D 46.6 F

73 US 17 29.5 D 43.6 E

41 US 17 24.3 C 31.3 D

4 Merge of US 17 and Folly Road 35.2 D 69.5 F

76 SC 61 41.2 E 46.3 F

72 SC 61 40.8 E 41.9 E

56 SC 61 41.5 E 41.7 E

55 SC 61 42.4 E 42.4 E

45 SC 61 42.9 E 42.9 E

44 SC 61 41.1 E 41.2 E

42 SC 61 27.3 C 27.3 C

7 Merge of US17/Folly Road and SC 61 37.1 E 62.4 F

77 T. Allen Legare Bridge 31.0 D 61.5 F

101 Lane Drop Before SC 61 31.9 D 55.9 F

Weighted Average 32.8 D 58.6 F

The average travel time results for the future 2028 conditions were computed using the same travel time segments and methodology as for 2016. As shown in Figure 3, the VISSIM simulation results for 2028 showed Folly Road traffic will continue to show the greatest change, with the average travel time projected to increase from 2.22 minutes to 4.44 minutes (representing an increase of approximately 133 seconds). SC 61 showed an increase from 1.78 minutes to 2.33 minutes (an increase of 34 seconds or 31%). US 17 is shown to have an increase in travel time from 1.80 minutes to 3.22 minutes (an increase of 85 seconds or 78.8%).


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Figure 3. Future Conditions (2028) Average Travel Time Results

Similar to the 2016 analysis, intersections in the immediate West Ashley area were analyzed to determine the impacts of the proposed Build condition. Table 7 summarizes the overall intersection delay and LOS for each intersection for the existing and Build conditions. An increase in delay was observed at all intersections in the study area since there were no changes in volumes, intersection geometry, and signal timings. Detailed results for the future conditions (2028) analysis are included in Appendix E.

Table 7. Future Conditions (2028) Intersection Operations

Alternative Primary Road Secondary Road Intersection

Delay (sec/veh) LOS

No Build (Existing)

SC 61 Wesley Drive 38.2 D



Folly Road Albemarle Road 13.0 B


Build

SC 61 Wesley Drive 40.2 D



Folly Road Albemarle Road 27.4 C

Lockwood Drive Bee Street 36.5 D

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

SC 61 US 17 Folly Rd All Roads

Ave

rage

Tra

vel T

ime

(min

)

Average Travel Time (2028)

No Build

Build

+33 sec / 31%

+85 sec / 79%

+133 sec / 100%

+88 sec / 75%


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3.6 Expected Year of Failure The results of the density analysis for the 2016 and 2028 Build scenarios were used to develop an expected year of failure for the overall bridge merge area. As mentioned previously, several segments showed increased delays to LOS F conditions but the overall area managed to be just under the threshold (45 veh/mi/ln) for failing conditions. To determine the year a failure, an interpolation was performed between the overall merge area densities for the 2016 and 2028 Build scenarios. Using the interpolation, it was determined that failing conditions along the bridge could be expected by 2017. Figure 4 summarizes the analysis performed. Additionally, all roadways saw an increase of at least 10% in travel times along all roadways in the study area in the 2016 analysis.

Figure 4. Average Build Density over Time

A qualitative analysis was performed on the roadway model to determine how effective the predicted mode shift would have to be to maintain the results from the 2016 Build analysis in 2028. The bridge currently sees 4,278 vehicles crossing over during the AM peak hour and this number is expected to grow to 4,689 vehicles by 2028. The 2016 Build analysis showed that the LOS expected along the bridge would be LOS E at 44.9 veh/mi/ln and increase to LOS F with an average density of 58.6 veh/mi/ln by 2028. It is assumed that if the volumes along the bridge remain the same in 2028 as in 2016, the simulated results observed in the 2016 Build scenario would be the same results observed in 2028. To maintain the same volume, the 411 additional vehicles being added over the next 12 years would have to be shifted to other modes of transportation to get across the bridge. At an average assumed rate of 1.2 persons per vehicle, this would result in a need of 493 people using other transportation modes including biking or walking along the new path during the AM peak hour in 2028.

25.0

30.0

35.0

40.0

45.0

50.0

55.0

60.0

65.0

2014 2016 2018 2020 2022 2024 2026 2028 2030

Ave

rage

Den

sity

(ve

h/m

i/ln)


August 2017 | 17

4 Summary This study has evaluated the traffic operational impacts that would occur if one travel lane were removed from the Northbound US 17 bridge over the Ashley River and its approach in order to accommodate a barrier-separated two-way shared use path in the space currently used by the fourth travel lane. This study is an update of the previous 2015 traffic study to incorporate data collected in 2016. A VISSIM traffic simulation model was calibrated to the existing travel time and volumes on the four-lane section and used to evaluate the operational changes that are projected to occur with the conversion of the bridge and its approach to a three-lane section.

The traffic study update indicates that the intersections in the surrounding areas would potentially experience minimal impacts from the lane reduction on the bridge. The roadway density in the bridge area indicates that the roadway is expected to experience failing traffic operational conditions in the 2028 Build scenario while also experiencing on average a 75% increase in travel time over the 2028 No Build scenario for all roadways in the study area.

Appendix

Appendix A:

2015 Ashley River Bridge Traffic Study Update

Ashley River Bridge Traffic Study Update T. Allen Legare Bridge (US 17 Northbound)

Charleston County Roadwise

Charleston, SC September 10, 2015


September 10, 2015 | i

Contents

Executive Summary ...................................................................................................................................... 1

Background ......................................................................................................................................... 1

Project Goals ....................................................................................................................................... 1

Evaluation Methodology ...................................................................................................................... 1

Key Findings ........................................................................................................................................ 1

Conclusion ........................................................................................................................................... 5

1 Introduction .......................................................................................................................................... 6

2 Data Collection and Field Observations .............................................................................................. 7

2.1 Traffic Counts ............................................................................................................................ 7

2.2 Historical Traffic Data .............................................................................................................. 12

2.3 Travel Time Runs .................................................................................................................... 12

2.4 Field Observations .................................................................................................................. 15

3 Evaluation of Three-Lane Roadway Section ..................................................................................... 18

3.1 Measures of Effectiveness ...................................................................................................... 18

3.2 Calibration of Existing Condition (2015) Simulation Model ..................................................... 19

3.3 Three Lane Section Configuration .......................................................................................... 23


3.5 Future Traffic Forecast ............................................................................................................ 28


3.7 Drawbridge Operations ........................................................................................................... 35

3.8 Analysis of Lane Change Volumes ......................................................................................... 35

3.9 Traffic Signal Operations ......................................................................................................... 37

4 Conclusions ....................................................................................................................................... 38

5 Appendices ........................................................................................................................................ 40

Tables

Table 1. HCM-Derived Composite Density LOS Thresholds ............................................................. 18

Table 2. Existing Condition (2015) Model - Travel Time Calibration ................................................. 19

Table 3. Existing Condition (2015) Model - Volume Calibration ........................................................ 23

Table 4. 2015 Level of Service .......................................................................................................... 27

Table 5. Existing Conditions (2015) Folly Road / Albemarle Road Intersection Operations .............. 28

Table 6. 2040 Level of Service .......................................................................................................... 33

Table 7. Future Conditions (2040) Folly Road / Albemarle Road Intersection Operations ................ 35

Table 8. Summary of Minimum Required Lane Changes .................................................................. 36

Table 9. Project Goals Evaluation Matrix .......................................................................................... 38


ii | September 10, 2015

Figures

Figure 1. Project Location Map and Traffic Count Locations ............................................................... 8

Figure 2. Northbound US 17 Bridge Daily Traffic Profile (March 2015) ............................................. 11

Figure 3. US 17 Bridges Historic Daily Traffic (2002-2014) ............................................................... 12

Figure 4. Travel Time Run Routes .................................................................................................... 13

Figure 5. Existing (2015) AM Peak Hour Traffic Volumes ................................................................. 20

Figure 6. Proposed Merge and Three-Lane Section Upstream of Bridge ......................................... 25

Figure 7. Proposed Configuration at Bee Street/Lockwood Drive Off-Ramp ..................................... 26

Figure 8. Existing Conditions (2015) Average Travel Time Results .................................................. 28

Figure 9. Projected Traffic Growth .................................................................................................... 30

Figure 10. Future (2040) AM Peak Hour Volumes ............................................................................ 31

Figure 11. Future Conditions (2040) Average Travel Time Results .................................................. 34

Appendices

Appendix A – Automated Roadway Traffic Counts

Appendix B – Turning Movement Counts

Appendix C – Travel Time Results

Appendix D – Existing Signal Timings

Appendix E – 2015 Simulation Results

Appendix F – BCDCOG Travel Demand Model Output

Appendix G – 2040 Simulation Results


September 10, 2015 | 1

Executive Summary

Background The four-lane T. Allen Legare Bridge on Northbound US 17 provides one of only two connections across the Ashley River from the West Ashley community into downtown Charleston. This bridge has been the topic of several studies to determine if it can be modified to safely accommodate bicycle and pedestrian traffic, including a previous 2011 traffic study that evaluated the potential impacts of eliminating one travel lane on the bridge and its immediate approach in order to accommodate a barrier-separated two-way shared use path in the space currently used as the fourth travel lane.

This study provides an update to the traffic analysis completed in 2011, and reflects traffic count data collected in 2015, as well as more recent regional travel demand model forecasts, which have been used to project traffic volumes forward to planning horizon year 2040. This study is intended to provide confirmation of the proposed design concept for the Build condition, including the proposed improvements at the Bee Street/Lockwood Drive off-ramp from Northbound US 17, and reflect future operations based on updated regional traffic forecasts.

Project Goals The No Build (existing) and Build conditions are being evaluated against four general project goals:

1. Safely accommodate multimodal mobility to and from the Charleston peninsula

2. Efficiently use existing infrastructure

3. Minimize impact to vehicle travel times

4. Minimize traffic impacts at intersections in the West Ashley community

Evaluation Methodology The evaluation has been completed through the use of the traffic engineering software VISSIM, which simulates the traffic operations of the area on the approach to the bridge, where Folly Road, US 17, and SC 61 merge together to create the existing four lane section. The VISSIM simulation is used due to the complex roadway and ramp configuration in the study area which has twelve possible origin-destination pairs and nine separate weaving sections.

Key Findings Traffic Counts

The peak traffic conditions last for less than two hours (7-8 AM, and a portion of the 8-9 AM hour), with drastically lower traffic volumes on the bridge over the other 22 to 23 hours of the day.


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Traffic volumes collected by SCDOT on the US 17 bridges (volumes are the sum of traffic on both the Northbound and Southbound bridges) have fluctuated up and down between 2002 and 2014, but the general daily volume trend has been relative flat (-0.3% per year decrease).

Traffic volumes collected by HDR on the approaches to the Northbound US 17 bridge showed the total volume on the bridge had grown by approximately 2% since previous counts were collected for the 2011 traffic study, resulting in an annual growth rate of about 0.5% per year between 2011 and 2015.

The 2011 traffic study used future traffic volume forecasts for year 2030, which were developed for the Charleston County Roadwise US 17/SC 61 Improvements Project, resulting in an average annual growth rate of 2.0%. Those traffic forecasts were based on the Berkeley Charleston Dorchester County of Governments (BCDCOG) adopted regional travel demand model that was in use at that time but developed prior to the severe recession that began in mid-2007. The current study update uses the latest travel demand model projections from the BCDCOG, which reflect less aggressive regional growth forecasts and a horizon year of 2040. The resulting annual growth rate is now 0.8%.



Build Concept Refinement

In addition to the shared use path, the current design concept for the Build condition improves vehicle capacity at the Bee Street / Lockwood Drive off-ramp by maintaining three through lanes on US 17 but also by adding a new exclusive left turn lane on the ramp. This improvement will decrease queuing and delay for vehicles exiting US 17 to Bee Street and northbound Lockwood Drive, resulting in smoother traffic flow at the off-ramp diverge point.

Analysis Results

The VISSIM simulation results for 2015 show only minor increases in travel times for each origin roadway through the study area due to the Build condition. With the improvements at the Bee Street / Lockwood Drive intersection, the travel times for SC 61 and US 17 are essentially unchanged in the Build condition. The analysis shows minor travel time increases on Folly Road due to the merge condition / lane drop; the average travel time on Folly Road is expected to increase from 1.98 minutes to 2.28 minutes (an increase of 15% or only 18 seconds) in the Build condition. A weighted average travel time across all three roadways shows an overall travel time increase of 8 seconds with the Build condition.

It is common traffic engineering practice to strive to achieve level of service (LOS) E on urban roadways during the AM and PM peak hours. In our study area, the most accurate metric for LOS is vehicle density (vehicles per mile per lane). The overall



average vehicle density results in acceptable levels of service for both the 2015 No Build (LOS C) and Build (LOS E) conditions. The change in LOS for the Build condition is not unexpected since the removal of one lane will have a direct effect on the overall average density of the study area. However, while density increased, the travel times through the study area did not change significantly as noted above.

There will be no changes to traffic operations at intersections in the West Ashley area in 2015 due to the Build condition, with the exception of minor changes in queuing and delay at the Folly Road / Albemarle Road intersection. However, the minor changes at this intersection do not result in a change in the overall intersection LOS (maintained at LOS B).

The VISSIM simulation results for 2040 continue to show only a minor increase in the average travel times across all roadways (2.20 minutes to 2.46 minutes, or a 16 second overall increase). With the Bee Street / Lockwood Drive intersection improvements, the travel times for SC 61 and US 17 are actually lower in the 2040 Build condition compared to the No Build condition with the existing intersection configuration. Folly Road traffic will continue to show the greatest change, with the average travel time projected to increase from 2.47 minutes to 3.34 minutes (representing an increase of about 50 seconds).

The overall average vehicle density (vehicles per mile per lane) in 2040 results in acceptable operations at LOS E for both the No Build and Build conditions. This result confirms that Build condition traffic operations will remain at acceptable levels through the planning horizon year 2040 based on the lower projected regional growth, in contrast to the results shown in the previous 2011 traffic study.

Intersections in the West Ashley area will not be impacted in 2040 due to the proposed Build condition, with the exception of minor changes at the Folly Road / Albemarle Road intersection. While delay and queuing at this intersection is shown to increase due to the Build configuration related to the downstream merge / lane drop condition, the intersection is shown to still operate acceptably at LOS E overall with the Folly Road approach at LOS D.



Conclusion In conclusion, the traffic study update confirms the findings of the previous 2011 traffic study and shows that only minor changes to traffic operations will occur with the Build condition based on today’s traffic volumes. Further, the lower regional growth projected by the BCDCOG travel demand model results in lower traffic forecasts to planning horizon year 2040 which are shown to result in acceptable traffic operations through 2040. The less aggressive growth rate is supported by the relatively flat traffic growth observed over the last ten years (which have been consistent during periods of growth and recession).

The proposed Build condition to add a shared use path in place of the fourth travel lane on the bridge and immediate approach achieves all of the stated project goals:

It provides a dedicated facility and safe route for bicycle and pedestrian travel between the West Ashley community and downtown Charleston which connects to the West Ashley Greenway.

It efficiently uses the existing infrastructure, which has excess capacity during the AM peak hour and large amounts of excess capacity in the other 22 to 23 hours of the day outside the AM peak period.

It is shown to result in only minor increases in vehicle travel times in both 2015 and 2040 analysis years. The average travel time for vehicles through the study area and crossing the bridge during the AM peak hour increases from 1.80 minutes to 1.94 minutes in 2015, and from 2.20 minutes to 2.46 minutes in 2040. This only represents average vehicle travel time increases of 7% and 12% for 2015 and 2040, respectively. Based on the peaking of traffic in the AM and considerably lower volumes outside the AM peak, there will be little to no increase in travel times for the other 22 to 23 hours of the day.

There will be no changes to traffic operations at intersections in the West Ashley area due to the proposed Build condition, other than minor changes at the Folly Road/Albemarle Road intersection which will still operate at acceptable levels of service in both 2015 (LOS B) and 2040 (LOS E).

Evaluation Criteria No Build (Existing) Build

Safely accommodate multimodal mobility to/from Charleston peninsula

No YES

Efficiently use existing infrastructure No YES

Minimize impact to vehicle travel times No YES

Minimize traffic impacts at intersections in West Ashley

YES YES



1 Introduction The Ashley River is the western boundary of downtown Charleston. Travel across the river near downtown is limited to US 17 (with Northbound traffic into downtown using the four-lane T. Allen Legare Bridge and Southbound traffic out of downtown using the three-lane World War I Memorial Bridge) and the Robert B. Scarborough (SC 30) Bridge. Both of these routes lack adequate bicycle and pedestrian facilities, which makes non-motorized travel across the Ashley River between the West Ashley community and downtown Charleston challenging and unsafe. The Northbound US 17 Bridge was identified to be the best candidate on which to construct a shared‐use path. Originally, the addition of a cantilevered pathway to the bridge was studied, but it was determined to be infeasible due to the loading constraints of the bridge bascule structure. The next alternative requested to be evaluated was the use of the outside lane of the Northbound US 17 Bridge as a barrier-separated shared use bicycle and pedestrian pathway, which would leave three lanes on the bridge for motorized traffic. The pathway would represent a major extension of the West Ashley Greenway, providing bicycle and pedestrian access between the West Ashley area and the Charleston peninsula.

The purpose of this study is to evaluate the impacts to motor vehicle traffic of eliminating one travel lane on the Northbound US 17 Bridge and its immediate approach in order to accommodate a barrier-separated two-way shared use path in the space currently used as the fourth travel lane. The evaluation has been completed through the use of the traffic engineering software VISSIM, which simulates the traffic operations of the area on the approach to the bridge, where Folly Road, US 17, and SC 61 merge together to create the existing four lane section. VISSIM analysis methods are used because the Highway Capacity Manual (HCM) methods are limited to freeway-ramp configurations and simple weave sections. However, the roadway and ramp configuration in the study area has multiple origin and destination points, which creates a complex section with twelve possible lane origin-destination pairs and nine separate weaving sections. Because the complex configuration of the study area exceeds the limitations of the HCM methods, the most appropriate way to evaluate the section is to simulate it.

This study provides an update to the traffic analysis completed in August 2011, and reflects traffic count data collected in 2015, as well as more recent regional travel demand model forecasts which have been used to project traffic volumes forward to horizon year 2040. The study is intended to provide confirmation of the proposed design concept, including the proposed improvements at the Bee Street/Lockwood Drive off-ramp from northbound US 17, and reflect future operations based on updated regional traffic forecasts. The No Build (existing) and Build conditions are being evaluated against four general project goals:

1. Safely accommodate multimodal mobility to and from the Charleston peninsula

2. Efficiently use existing infrastructure

3. Minimize impact to vehicle travel times

4. Minimize traffic impacts at intersections in the West Ashley community



2 Data Collection and Field Observations Based on previous studies and traffic data, the highest volumes of the day on the Northbound US 17 Bridge occur during the AM peak period. As such, the data collection for this project focused on conditions during the AM peak, corresponding with commuter traffic traveling into downtown Charleston from the West Ashley community. The data included roadway counts using automatic traffic recorders (ATRs), AM peak period intersection turning movement counts, and travel time runs.

Field observations were performed by the study team in March 2015, and included observations of traffic flow, vehicle platooning, queues, and weaving and merging characteristics.

2.1 Traffic Counts 72-hour roadway segment traffic counts were collected at the following locations in March and April 2015 to support the development of the VISSIM traffic simulation model:

1. SC 61 Ramp to Northbound US 17

2. Northbound US 17, south of (prior to) merge with Folly Road

3. Folly Road, north of Albemarle Road

4. Northbound US 17, north of the Bee Street/Lockwood Drive Off-Ramp

5. Northbound US 17 Off-Ramp, Eastbound Bee Street/Northbound Lockwood Drive

6. Northbound US 17 Off-Ramp, free flow lane to Southbound Lockwood Drive

AM peak period (7-9 AM) turning movement counts were collected at thirteen (13) signalized intersections in March and April 2015 in the West Ashley area, as well immediately downstream of the bridge in downtown Charleston, as follows:

1. US 17 and Magnolia Road

2. US 17 and Avondale Avenue

3. US 17 and Stocker Drive

4. US 17 and SC 171/Wesley Drive

5. Folly Rd and Albemarle Road

6. Folly Rd and SC 171/Wesley Drive

7. Folly Rd and Windermere Boulevard

8. Folly Rd and Yeamans Road

9. Folly Rd and Formosa Drive

10. SC 61 and Riverdale Drive

11. SC 61 and SC 171/Wesley Drive

12. Northbound US 17 Off-Ramp/Lockwood Drive

13. Southbound US 17 On-Ramp/Lockwood Drive

Lockwood Dr

Ashley River Bridge Traffic Study

Bee St

US 17 Southbound

US 17 Northbound

Wes

ley

DrFolly Rd

Folly

Rd

12

13

5

4

6

7

8

9

11

10

3

21

Stocker Dr

Riverdale Dr

Avondale Ave

Magnolia Rd

Paris

h Rd

SC 61

US 17

Yeamans Rd

Formosa Dr

Windermere Blvd

Albemarle Rd

Figure 1 | Project Location Map and Traffic Count Locations

72- Hour Automatic Traffic Recorder (ATR) CountAM Peak Period Turning Movement Count (7-9 am)

Legend:

X

4

12

3

X

6

5


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Figure 1 shows the study area and traffic count locations. These locations represent the key roadway segments and intersections on the immediate approach to the bridge and the immediate departure area from the bridge into downtown Charleston. All traffic counts are provided in Appendix A (Automated Roadway Traffic Counts) and Appendix B (Turning Movement Counts).

Figure 2 shows the average 24-hour traffic profile from the 72-hour counts for the Northbound US 17 bridge and the three immediate roadway approaches on US 17, SC 61, and Folly Road. As shown, the highest traffic volumes occur from 7-8 AM, with slightly lower volumes from 8-9 AM. However, traffic volumes on the bridge in all other hours of the day are dramatically lower. As such, the duration of the traffic conditions of most concern is less than two hours of the day.

Figure 2. Northbound US 17 Bridge Daily Traffic Profile (March 2015)

Source: HDR.

The AM peak hour intersection turning movement volumes were used to develop the peak hour volumes for simulation in VISSIM. Turning traffic volumes were balanced through the network, conservatively using higher volumes when there was a discrepancy between two competing numbers. As a result, the peak hour volume on the bridge included in the simulation was higher than those shown in Figure 2, at approximately 4,250 vehicles per hour. This peak hour volume was also higher than the peak hour volume on the bridge used in the 2011 traffic study (4,147 vehicles per hour).

The measured percentage of heavy vehicles from the roadway segment counts during the AM peak hour varied from 0.9% on Folly Road to 2.2% on SC 61 on the upstream side of the bridge, and from 0.6% for the eastbound left and through movements to


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Lockwood Drive and Bee Street to 2.5% for the eastbound right turn movement to southbound Lockwood Drive. Because these values were similar to the global 2% heavy vehicle value used previously in the 2011 Ashley River Bridge VISSIM analysis, the global 2% heavy vehicle value was maintained for this project update.

2.2 Historical Traffic Data The SCDOT annual traffic count program includes a count station located on the US 17 bridge (which includes both the northbound and southbound bridges). Traffic data from 2002 through 2014 (the most recent year for which data was available) shows that traffic volumes on the bridges have fluctuated slightly from year to year but the overall growth has been slightly negative (-0.3% per year). Figure 3 presents the SCDOT historic daily traffic counts on the US 17 bridges.

Figure 3. US 17 Bridges Historic Daily Traffic (2002-2014)

Source: SCDOT.

2.3 Travel Time Runs Travel time is the critical measure of effectiveness (MOE) for the analysis of this project, and as such, existing travel time data was collected for each of the three roadways that converge to make up the four-lane section on Northbound US 17. Travel time runs were completed during the AM peak period (7-9 AM) for SC 61, US 17, and Folly Road on the routes shown in Figure 4, each ending on the Bee Street/Lockwood Drive Off-Ramp. The existing condition travel time results were used to calibrate the VISSIM model, and then to compare the projected travel times based on the proposed three-lane section. Travel time results are provided in Appendix C.

SC 61

Lockwood Dr


Bee St

US 17 Southbound

US 17 Northbound

Folly Rd

Wes

ley

Dr

Albemarle Rd

US 17

US 17 Northbound

SC 61 Ramp

Figure 4 | Travel Time Run Routes

Folly Rd from Albemarle Rd to Bee St Travel Time Run Route

US 17 from Wesley Dr Northbound to Bee St Travel Time Run Route

SC 61 from Wesley Dr to Bee St Travel Time Run Route

Legend:


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2.4 Field Observations The following observations were made during the AM peak period for the study area:

Observed traffic flows during the AM peak period (7-9 AM) were relatively heavy within the four-lane section on US 17 Northbound on the bridge and the approach to the bridge. However, the volumes and lane changing maneuvers in this section rarely resulted in any noticeable speed decreases and the traffic remained in a free-flow condition. The slowdowns that were observed were typically the result of a single vehicle making a lane change during a short period of heavy traffic flow, affecting only the vehicles accommodating the maneuver; once the lane change was complete, free-flow conditions were quickly resumed.

AM peak hour traffic flow in the four-lane section approaching the bridge (looking south).

Traffic flow is regulated by the upstream signals on each of the three roadways that join together to make up the four-lane section. Signal operations were observed during the AM peak period along Wesley Drive between Folly Road and SR 61. The signals appeared to stay in coordination throughout the hour. It had previously been observed in 2011 that vehicle platoons from each signal generally arrived at the four-lane bridge approach section at about the same time, creating periods of heavier traffic flow followed by shorter periods with very little traffic. However, closer review of the signal operations in 2015 showed that the through movements for US 17 and SR 61 toward the bridge do have staggered green phases, which results in traffic flows from these roadways reaching the bridge at different times. Further discussion is provided later in the report regarding the feasibility of signal coordination modifications to further separate the vehicle platoons on the three roadways to provide for more uniform traffic flow on the bridge and its immediate approach.

The Folly Road approach to the four-lane section has relatively uniform lane utilization. Based on field observations, approximately 55% of the Folly Road traffic uses the outside lane, with 45% using the inside lane.

The lane merge for the Northbound US 17 approach to the four-lane section occurs suddenly over a short distance (approximately 375 feet from the first sign and


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pavement markings informing motorists the left lane ends and to merge right). Because the majority of drivers during the AM peak are likely commuters who drive the corridor regularly and know about the sudden lane merge, it was observed that most drivers had already merged into the right lane prior to the lane merge.

The short US 17 merge area on the approach to the Northbound US 17 bridge.

On the north side of the Northbound US 17 Bridge, the four lane section splits with three lanes continuing on Northbound US 17, and a two-lane off-ramp to Bee Street and Lockwood Drive. In this configuration, the second lane from the right (in the direction of travel) allows traffic to either exit to the off-ramp or continue on Northbound US 17. Along the off-ramp, the left lane provides access to Bee Street and Northbound Lockwood Drive via a signalized intersection, while the right lane is a free flow movement onto Southbound Lockwood Drive. Queues from the Bee Street/Lockwood Drive off-ramp signal were observed to back up near the end of the off-ramp, but rarely observed to back onto the US 17 mainline or affect diverging traffic operations at the off-ramp.

(Left) The diverge area on Northbound US 17 at the Bee Street / Lockwood Drive off ramp with three lanes continuing on US 17 and a two-lane off-ramp. (Right) Queuing on the Bee Street / Lockwood Drive off-ramp.

No pedestrians or bicyclists were observed using the Northbound US 17 Bridge, although this is expected due to the lack of dedicated facilities (only an approximate


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two-foot wide curb located adjacent to the low bridge railing is available). However, there were a number of pedestrians and bicyclists observed using the Southbound US 17 Bridge, which provides an approximate four-foot wide sidewalk at the back of curb on the outside of the bridge. Along this sidewalk, bicyclists were observed traveling in both directions. Although no instances were observed in which bicyclists traveling in opposite directions met on the bridge or bicyclists encountered pedestrians (in either direction), the narrow sidewalk width would make passing very challenging and dangerous in this situation.

Bicyclists observed on and near the Southbound US 17 bridge traveling north (left photo) and south (right photo).

No drawbridge activity was observed during the field review. Activation of the drawbridge during the AM peak period would result in queues extending into the area of the junction of US 17, Folly Road, and SC 61. At the completion of a drawbridge cycle when traffic began to move again, weaving operations would be negatively affected due to the higher traffic demand and greater vehicle density within the four-lane section.


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3 Evaluation of Three-Lane Roadway Section The evaluation of the removal of one travel lane on the Northbound US 17 Bridge and its approach in order to accommodate a barrier-separated shared use path was completed using the traffic simulation software, VISSIM. VISSIM is a microsimulation software that is widely used across the country to evaluate traffic operations within complex geometric configurations. VISSIM was previously used to evaluate the traffic operations in the West Ashley community as part of the RoadWise US 17/SC 61 Improvements Project and was used for the Ashley River Bridge Traffic Study in 2011. VISSIM allows the impacts of downstream disturbances and capacity issues to propagate back through the model; therefore, the traffic operation within each individual segment is influenced by the operations in adjacent segments and the study area as a whole. In contrast, the methods used in the HCM only look at isolated locations and do not fully account for queue spillback in the analysis.

3.1 Measures of Effectiveness The MOEs that will be used in this project include travel time, density (vehicles per mile per lane), and level of service (LOS). As mentioned previously, travel time is the critical MOE because the reduction of a travel lane will more greatly affect the roadway density and LOS. However, even if traffic flow is denser, the difference in travel time through the study area may not change significantly.

It is common traffic engineering practice to strive to achieve LOS E on urban roadways during the peak hours. To determine an overall LOS for the entire study area, an average of the LOS thresholds for density was computed from the thresholds in the 2010 HCM for various facility types including multilane highway basic sections, multilane highway weaving sections, and ramp junctions (merge/diverge areas). This approach is used because the section in question is complex and cannot be defined by any one facility type. The average of thresholds from multiple facility types results in a single set of LOS values, which are shown in Table 1. The VISSIM simulation reports a density, volume and speed for each link segment by lane. Using weighted averages based on link volume, a weighted average density can be developed for each alternative.

Table 1. HCM-Derived Composite Density LOS Thresholds

LOS Multilane Highway

(veh/mi/ln)

Multilane Highway Weaving

(veh/mi/ln) Ramp Junction

(veh/mi/ln) Average

(veh/mi/ln)

A 11 12 10 11.0

B 18 24 20 20.7

C 26 32 28 28.7

D 35 36 35 35.3

E 45 a a 45.0

Source: Transportation Research Board (TRB) Highway Capacity Manual (HCM) 2010. Average values account for multiple facility types across the analysis segment a LOS F is reached when demand exceeds capacity, but no specific density threshold defines that point.


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3.2 Calibration of Existing Condition (2015) Simulation Model Calibration of any simulation model is important to achieving reliable results. The existing model was calibrated based on several inputs, most importantly of which is travel time based on the series of travel time runs completed from each of the three roadway origin points to the Bee Street/Lockwood Drive Off-Ramp. Several other model inputs were adjusted to help calibrate travel time, including desired free flow speed curves designed for each study segment, and driver parameters in merge areas.

The average of the measured existing conditions travel times based on the travel time runs completed for each roadway on the routes shown previously in Figure 4 are summarized in Table 2. The calibration of 2015 existing conditions in the VISSIM model included a comparison of the average results from five (5) simulation runs to the measured average travel time based on the same route limits. The simulated travel time for each roadway was within 5% of the measured average travel time, which is well within the recommended industry tolerance of 15% to consider the model acceptably calibrated.

Table 2. Existing Condition (2015) Model - Travel Time Calibration

Roadway Measured Travel

Time (min) VISSIM Travel

Time (min) % Difference

SC 61 1.50 1.42 -5%

US 17 1.45 1.50 4%

Folly Rd 1.31 1.29 -1%

Figure 5 shows the existing 2015 AM peak hour volumes on the roadways within the study area. As shown, the Folly Road approach has the highest peak hour volume, with US 17 contributing the second highest volume, and SC 61 the lowest. In total, the four-lane section on the bridge and its immediate approach has an AM peak hour volume of nearly 4,250. Figure 5 also shows the volumes traveling from each origin point to each destination point within the study area.

To calibrate the volumes, the VISSIM output for the five runs was compared to the existing 2015 volumes. These volumes represent the total number of vehicles that are recorded in and processed through the simulation network, and are directly comparable to the measured traffic counts. In order to achieve proper calibration, the average VISSIM volumes should be within 15% of the existing volumes.

As shown in Table 3, the average volume for each of the three origin roadways was well within the 15% threshold. With the favorable travel time and volume results, the existing 2015 model is considered calibrated.

The traffic signals coded in the VISSIM model use the existing signal timings provided by the City of Charleston. See Appendix D for the provided signal timings.


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2581

1136

4249

1306 1807

620

1048

F

C

B

A

E

D

SC 61

Lockwood Dr


Bee St

US 17 Southbound

US 17 Northbound

Folly Rd

Wes

ley

Dr

Albemarle Rd

US 17

US 17 Northbound

SC 61 Ramp

Figure 5 | Existing (2015) AM Peak Hour Traffic Volumes

From To AM Peak Hour Volume

A D 446

A E 264

A F 1097

B D 322

B E 190

B F 794

C D 280

C E 166

C F 690

TOTAL 4249

Origin or Destination Point

Total AM Peak Hour Traffic

Legend:X

XX


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Table 3. Existing Condition (2015) Model - Volume Calibration

Roadway

Measured Target AM Peak Hour

Volume

VISSIM Average AM Peak Hour

Volume % Difference

US 17 1,306 1,253 -4%

SC 61 1,136 1,131 0%

Folly Rd 1,807 1,857 3%

NB US 17 Bridge 4,249 4,249 0%

3.3 Three Lane Section Configuration Based on the previous traffic studies completed and alternatives evaluated in the West Ashley community, there were limited new options available for eliminating one travel lane on the Northbound US 17 Bridge and its approach. Because it was desired to maintain the single lane for the SC 61 ramp as a lane addition to the Northbound US 17 section approaching the bridge rather than having this ramp merge into the section, and because US 17 already merges to a single lane, the most feasible option for removing a lane was to merge the two lanes from the Folly Road approach into a single lane. This would result in each roadway (SC 61, US 17, and Folly Road) contributing one lane to the three-lane section. To limit the amount of retaining wall and structure needed for the shared use path along the marshy roadside leading up to the bridge, the current concept includes merging the Folly Road traffic within approximately 900 feet from the Albemarle Road intersection, as shown in Figure 6. The merge is located within the tangent section of Folly Road and just prior to the location where Folly Road joins Northbound US 17.

At the downstream end of the bridge, capacity improvements are proposed at the Bee Street/Lockwood Drive Off-Ramp to add an exclusive left turn lane to the intersection approach, thereby resulting in a three lane ramp section. This improvement will be constructed before the lane reduction on the bridge is implemented and will maintain the existing two-lane off-ramp configuration. In the Build condition, the off-ramp would be reduced to a single lane at the diverge point from Northbound US 17, but expand immediately to three lanes. Figure 7 shows the proposed lane configuration in both the interim and Build conditions. This improvement will decrease queuing and delay for vehicles exiting US 17 to Bee Street and northbound Lockwood Drive, resulting in smoother traffic flow at the off-ramp diverge point.


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Figure 6. Proposed Merge and Three-Lane Section Upstream of Bridge

Proposed Build Conf guration

Interim Interchange Ramp Improvement

Barrier-separated shared used path

SC 61

Lockwood Dr


Bee St

US 17 Southbound

US 17 Northbound

Folly Rd

Wes

ley

Dr

Albemarle Rd

US 17

US 17 Northbound

SC 61 Ramp

Figure 7 | Three Lane Section Alternatives at Bee Street / Lockwood Drive Off-Ramp


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3.4 2015 Analysis Results As discussed earlier, travel times were one of the metrics used to evaluate the performance of the alternatives. Travel time results from VISSIM were computed for each roadway based on a weighted average of the travel times between each origin-destination pair (four destination points for each originating roadway). An overall weighted average was also computed across all roadways. The travel times for each originating roadway included the intersection approach at the Bee Street/Lockwood Drive signal to capture the reduced delays and queuing due to the proposed improvements at that location in the Build condition. Also, the travel times for Folly Road included the segment between Wesley Drive and Albemarle Drive to account for any delays at the Albemarle Road due to the lane merging that would happen just downstream from the intersection in the Build condition.

The results of the VISSIM analysis for the 2015 existing conditions in Table 4 show that the overall average vehicle density within the study area results in acceptable levels of service for both the 2015 No Build (LOS C) and Build (LOS E) conditions. The change in LOS for the Build condition is not unexpected since the removal of one lane will have a direct effect on the overall average density of the study area. However, while density increased, the travel times through the study area did not significantly change. As shown in Figure 8, the average travel time for Folly Road traffic is projected to increase by only 18 seconds in the Build condition compared to the existing condition. Overall, the average additional travel time across all roadways in the Build condition is estimated at only 8 seconds more than the existing condition. Detailed analysis results for the existing conditions (2015) analysis are included in Appendix E.


Alternative Average Density

(veh/mi/ln) LOS

No Build (Existing) 28.6 C

Build 38.0 E

It is important to note that the Build configuration would not change the intersection operations at the upstream intersections in the West Ashley area because no volumes, lane configurations, or signal timings are proposed to be changed in this area. The only intersection anticipated to have minor increases in delay is the Folly Road / Albemarle Road intersection; the Folly Road approach headed towards downtown Charleston will have a minor delay increase to due to the downstream merge required at the lane drop point. Table 5 summarizes the maximum queues, average delay, and LOS for each approach and the overall intersection for the existing and Build conditions at the Folly Road / Albemarle Road intersection. As shown, the maximum queues will increase more significantly on Folly Road, but the average delay change only decreases the LOS on that approach to LOS B.


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Figure 8. Existing Conditions (2015) Average Travel Time Results

Table 5. Existing Conditions (2015) Folly Road / Albemarle Road Intersection Operations

Alternative Approach Max Queue (ft) Approach Delay

(sec/veh) LOS

No Build (Existing)

EB: Folly Rd 264 3.6 A

NB: Albemarle Rd 186 25.6 C

SB: Ramp to Albemarle Rd 256 59.0 E

Overall Intersection --- 10.9 B

Build

EB: Folly Rd 785 11.4 B

NB: Albemarle Rd 288 43.3 D



3.5 Future Traffic Forecast The future traffic forecasts for this study were developed based on projections from the Berkeley Charleston Dorchester Council of Governments (BCDCOG) regional travel demand model. The BCDCOG provided model-projected traffic volumes for three scenarios:

2010 base year model – this represents the existing socioeconomic data (population and employment) and roadway network from year 2010.


September 10, 2015 | 29

2040 existing + committed (E+C) model – this represents the projected year 2040 socioeconomic data (population and employment) with the existing roadway network plus projects with committed construction funding in the 5-year Transportation Improvement Program (TIP).

2040 Long Range Transportation Plan (LRTP) model – this represents the projected year 2040 socioeconomic data (population and employment) with the proposed cost feasible roadway network from the LRTP. One of the roadway improvements included in the cost feasible roadway network for 2040 is the Mark Clark Expressway Extension, connecting between I-526 at US 17 and the James Island Connector at Folly Road.

The growth in traffic volumes between the 2010 base year model and the 2040 E+C model on the Northbound US 17 bridge was used as the growth percentage that was applied to existing balanced AM peak hour turning movement volumes in the study area. Future 2040 balanced traffic volumes on the Northbound US 17 bridge represented a 0.8% annual growth rate. In comparison, the previous 2011 traffic study used future traffic volume forecasts for year 2030, which were developed for the Charleston County Roadwise US 17/SC 61 Improvements Project, resulting in an average annual growth rate of 2.0%. Those traffic forecasts were based on the BCDCOG adopted regional travel demand model that was in use at that time; however, it should be noted that the previous model was developed prior to the severe recession that began in mid-2007. The current travel demand model projections from the BCDCOG reflect less aggressive regional growth forecasts and a horizon year of 2040. Figure 9 provides a comparison of the current and previous traffic volumes and growth assumptions.

The 2040 LRTP model projections were obtained to determine the potential impact of the Mark Clark Expressway Extension on the traffic volumes on the Northbound US 17 bridge and its immediate approach in the West Ashley community. Compared to the 2040 E+C model, the 2040 LRTP model shows the daily traffic volumes on the Northbound US 17 to be approximately 3% lower. With only minor decreases in traffic volumes on the Northbound US 17 bridge projected with the Mark Clark Expressway Extension in place, this study focuses on the more conservative E+C scenario for the future year conditions in 2040.

Figure 10 shows the projected 2040 AM peak hour volumes on the roadways within the study area, as well as the volumes traveling from each origin point to each destination point within the study area.

Daily traffic volumes from the BCDCOG travel demand model are provided in Appendix F.


30 | September 10, 2015

Figure 9. Projected Traffic Growth

3135

1371

1551215

1

762

1176

F

C

B

A

E

D

5073SC 61

Lockwood Dr


Bee St

US 17 Southbound

US 17 Northbound

Folly Rd

Wes

ley

Dr

Albemarle Rd

US 17

US 17 Northbound

SC 61 Ramp

Figure 10 | Future (2040 without MCE ) AM Peak Hour Traffic Volumes

From To AM Peak Hour Volume

A D 499

A E 323

A F 1329

B D 359

B E 233

B F 959

C D 318

C E 206

C F 847

TOTAL 5073

Origin or Destination Point

Total AM Peak Hour Traffic

Legend:X

XX


32 | September 10, 2015



September 10, 2015 | 33

3.6 2040 Analysis Results The results of the VISSIM analysis for the 2040 future conditions in Table 6 show that the overall average vehicle density in the study area results in acceptable operations at LOS E for both the No Build and Build conditions. This result confirms that Build condition traffic operations will remain at acceptable levels through the planning horizon year 2040 based on the lower projected regional growth, in contrast to the results shown in the previous 2011 traffic study.


Alternative Average Density

(veh/mi/ln) LOS

No Build (Existing) 35.8 E

Build 44.0 E

The average travel time results for the future 2040 conditions were computed using the same travel time segments and methodology as for 2014. As shown in Figure 11, the VISSIM simulation results for 2040 continue to show only a minor increase in the average travel times across all roadways (2.20 minutes to 2.46 minutes, or a 16 second overall increase). With the Bee Street / Lockwood Drive intersection improvements, the travel times for SC 61 and US 17 are actually lower in the 2040 Build condition compared to the No Build condition with the existing intersection configuration; this results primarily because of lower intersection delay at the Bee Street / Lockwood Drive off-ramp compared to the No Build condition. Folly Road traffic will continue to show the greatest change, with the average travel time projected to increase from 2.47 minutes to 3.34 minutes (representing an increase of about 50 seconds).


34 | September 10, 2015

Figure 11. Future Conditions (2040) Average Travel Time Results

Detailed analysis results for the future conditions (2040) analysis are included in Appendix G.

Similar to the 2015 analysis, intersections in the West Ashley area will not be impacted in 2040 due to the proposed Build condition, because no volumes, lane configurations, or signal timings are proposed to be changed in this area. The one exception is minor changes at the Folly Road / Albemarle Road intersection. Table 7 summarizes the maximum queues, average delay, and LOS for each approach and the overall intersection for the existing and Build conditions at the Folly Road / Albemarle Road intersection. While delay and queuing at this intersection is shown to increase due to the Build configuration related to the downstream merge / lane drop condition, the intersection is shown to still operate acceptably at LOS E overall with the Folly Road approach at LOS D.


September 10, 2015 | 35

Table 7. Future Conditions (2040) Folly Road / Albemarle Road Intersection Operations

Alternative Approach Max Queue (ft) Approach Delay

(sec/veh) LOS

No Build (Existing)

EB: Folly Rd 447 14.3 B

NB: Albemarle Rd 272 28.2 C



Build

EB: Folly Rd 1,181 49.6 D

NB: Albemarle Rd 984 110.3 F


Overall Intersection --- 59.7 E

3.7 Drawbridge Operations The traffic simulation does not take into consideration the conditions during a drawbridge activation event since such an event does not typically occur during the AM peak hour. It should be noted that implementing the recommended three-lane alternative would result in queue storage for 94 fewer vehicles on the bridge and its immediate approach during a drawbridge activation event. This reduction was computed by measuring the lane length that would be eliminated, measured from the lane merge point to the draw bridge stop bar (approximately 2,350 feet) and dividing by the average vehicle storage length of 25 feet. However, as discussed earlier, the traffic volumes approaching the bridge are substantially lower during all hours of the day outside of the 7-9 AM peak period. With a substantial amount of queue storage available to the closest upstream traffic signals, a drawbridge activation event outside of the AM peak hour is not a concern, even with one fewer lane available to store vehicles.

3.8 Analysis of Lane Change Volumes The proposed Build configuration will result in differences in the number of lane changes required to get from specific origin points to specific destination points on the Northbound US 17 bridge and its immediate approach. Table 8 presents a summary of the minimum lane changes required based on the 12 possible origin-destination pairs under the No Build configuration (existing four lane section) and the proposed Build configuration (three lane section). The table lists the volume for each origin-destination pair, the minimum number of lane changes required to get from the origin to the destination, and the total lane change volume. Volumes for both 2015 and 2040 are represented.

As shown in Table 8, the No Build (existing) four-lane section results in a minimum of 2,955 lane changes from the total 2015 AM peak hour volume of 4,249 vehicles on the bridge. However, the proposed three-lane Build configuration would only result in 2,397 required lane changes – a decrease of about 19%. In 2040, the Build configuration would result in a reduction of lane changes from 3,451 to 2,823, an approximate 18% reduction. Fewer required lane changes will result in smoother, more efficient traffic operations on the bridge and its approach.


36 | September 10, 2015

Table 8. Summary of Minimum Required Lane Changes

Origin Destination

No Build (4-Lane Section) Build (3-Lane Section)

Volume

Min # Lane

Changes

Total Lane

Changes Volume

Min # Lane

Changes

Total Lane

Changes

Existing Conditions (2015) Volumes

A: Folly Rd (outside lane)a D: Lockwood Dr SB 245 0 0 245 1 245

A: Folly Rd (outside lane)a E: Bee St / Lockwood NB 145 1 145 145 1 145

A: Folly Rd (outside lane)a F: US 17 North 603 1 603 603 1 603

A: Folly Rd (inside lane)a D: Lockwood Dr SB 201 1 201 201 0 0

A: Folly Rd (inside lane)a E: Bee St / Lockwood NB 119 0 0 119 0 0

A: Folly Rd (inside lane)a F: US 17 North 494 0 0 494 0 0

B: US 17 NB D: Lockwood Dr SB 322 2 644 322 1 322

B: US 17 NB E: Bee St / Lockwood NB 190 1 190 190 1 190

B: US 17 NB F: US 17 North 794 0 0 794 0 0

C: Ramp from SC 61 D: Lockwood Dr SB 280 3 840 280 2 560

C: Ramp from SC 61 E: Bee St / Lockwood NB 166 2 332 166 2 332

C: Ramp from SC 61 F: US 17 North 690 0 0 690 0 0

Total 4,249 --- 2,955 4,249 --- 2,397

Future Conditions (2040) Volumes

A: Folly Rd (outside lane)a D: Lockwood Dr SB 274 0 0 274 1 274

A: Folly Rd (outside lane)a E: Bee St / Lockwood NB 178 1 178 178 1 178

A: Folly Rd (outside lane)a F: US 17 North 731 1 731 731 1 731

A: Folly Rd (inside lane)a D: Lockwood Dr SB 225 1 225 225 0 0

A: Folly Rd (inside lane)a E: Bee St / Lockwood NB 145 0 0 145 0 0

A: Folly Rd (inside lane)a F: US 17 North 598 0 0 598 0 0

B: US 17 NB D: Lockwood Dr SB 359 2 718 359 1 359

B: US 17 NB E: Bee St / Lockwood NB 233 1 233 233 1 233

B: US 17 NB F: US 17 North 959 0 0 959 0 0

C: Ramp from SC 61 D: Lockwood Dr SB 318 3 954 318 2 636

C: Ramp from SC 61 E: Bee St / Lockwood NB 206 2 412 206 2 412

C: Ramp from SC 61 F: US 17 North 847 0 0 847 0 0

Total 5,073 --- 3,451 5,073 --- 2,823

Source: HDR. a Assumes 55% of existing Folly Rd traffic uses outside lane, and 45% uses inside lane, based on field observations.


September 10, 2015 | 37

3.9 Traffic Signal Operations Traffic flow to the Northbound US 17 bridge and its immediate approach is regulated by the upstream signals on each of the three roadways that join together to make up the existing four-lane section. Signal operations were observed during the AM peak period along Wesley Drive between Folly Road and SR 61. The signals appear to stay in coordination throughout the hour. It had previously been observed in 2011 that vehicle platoons from each signal generally arrived at the four-lane bridge approach section at about the same time, creating periods of heavier traffic flow followed by shorter periods with very little traffic. However, closer review of the signal operations in 2015 showed that the through movements for US 17 and SR 61 toward the bridge do have staggered green phases, which results in traffic flows from these roadways reaching the bridge at different times.

It had been suggested in the 2011 study that offsetting the upstream intersection signal timings might be possible such that vehicle platoons would not arrive at the merge area concurrently. Spreading the arrivals of vehicle platoons from the three originating roadways’ upstream signals would benefit the bridge and its approach by reducing vehicle densities in that section. Ideally, this would spread the traffic loading on the bridge and its approach more evenly, resulting in less pronounced periods of heavy traffic followed by periods of very light traffic. However, after a more thorough review of the existing signal timings, a change in signal offsets or cycle lengths is not recommended at this time. Based on the review, it was determined that these type of changes would likely only provide minor improvements to the traffic flow on Northbound US 17, while having the potential to disrupt current signal progression in the West Ashley area, thereby resulting in increased delay and queuing. Improvements in overall traffic flow and efficiency would be gained by updating and optimizing the signal phase split times at locations throughout the West Ashley area. Signal timing optimization has the potential to help offset any travel time losses that may be experienced based on the conversion to a three-lane section on the bridge and its approach.

It is important to recognize that traffic flow on the bridge and its immediate approach is generally free flow, and any delays experienced in this section are generally the result of traffic control located further downstream (e.g., in downtown Charleston). The improvements at the Bee Street/Lockwood Drive off-ramp will help to alleviate one potential bottleneck that may result in queues that would affect through traffic on Northbound US 17. In addition, the upstream traffic signals in the West Ashley area meter traffic traveling towards the bridge and its approach; therefore, the free flow bridge does not represent the critical segment, even with only three travel lanes. As traffic volumes continue to grow in the future, it is possible that the entire demand traffic flow may not be able to clear the upstream signalized intersections to even provide the full demand volume to the bridge and its immediate approach.

.


38 | September 10, 2015

4 Conclusions This study has evaluated the traffic operational impacts that would occur if one travel lane were removed from the Northbound US 17 Bridge over the Ashley River and its approach in order to accommodate a barrier-separated two-way shared use path in the space currently used by the fourth travel lane. The study is an update of the previous 2011 traffic study, which incorporates 2015 traffic count data and the latest regional future traffic projections. A VISSIM traffic simulation model was calibrated to the existing travel time and volumes on the four-lane section and used to evaluate the operational changes that are projected to occur with the conversion of the bridge and its approach to a three-lane section.

In conclusion, the traffic study update confirms the findings of the previous 2011 traffic study and shows that only minor changes to traffic operations will occur with the Build condition based on today’s traffic volumes. Further, the lower regional growth projected by the BCDCOG travel demand model results in lower traffic forecasts to planning horizon year 2040 which are shown to result in acceptable traffic operations through 2040. The less aggressive growth rate is supported by the relatively flat traffic growth observed over the last ten years (which have been consistent during periods of growth and recession).

Table 9 presents an evaluation matrix of the stated project goals.

Table 9. Project Goals Evaluation Matrix

Evaluation Criteria No Build (Existing) Build

Safely accommodate multimodal mobility to/from Charleston peninsula

No YES

Efficiently use existing infrastructure No YES

Minimize impact to vehicle travel times No YES

Minimize traffic impacts at intersections in West Ashley

YES YES

As shown, the proposed Build condition to add a shared use path in place of the fourth travel lane on the bridge and its immediate approach achieves all of the stated project goals:

It provides a dedicated facility and safe route for bicycle and pedestrian travel between the West Ashley community and downtown Charleston which connects to the West Ashley Greenway. In contrast, having no dedicated bicycle facility between West Ashley and downtown Charleston in the No Build condition serves as a huge barrier to safe multimodal access and mobility between these communities.

It efficiently uses the existing infrastructure, which has excess capacity during the AM peak hour and large amounts of excess capacity in the other 22 to 23 hours


September 10, 2015 | 39

of the day outside the AM peak period. It would also result in 18-19% fewer lane changes required compared to the existing four-lane configuration.

It is shown to result in only minor increases in vehicle travel times in both 2015 and 2040 analysis years. The average travel time for vehicles through the study area and crossing the bridge during the AM peak hour increases from 1.80 minutes to 1.94 minutes in 2015, and from 2.20 minutes to 2.46 minutes in 2040. This only represents average vehicle travel time increases of 7% and 12% for 2015 and 2040, respectively. Based on the peaking of traffic in the AM and considerably lower volumes outside the AM peak, there will be little to no increase in travel times for the other 22 to 23 hours of the day. The No Build condition, which also assumes no improvements to the Bee Street/Lockwood Drive off-ramp, would not result in minimized travel times as delays and queuing from the Bee Street/Lockwood Drive intersection would worsen to the point of causing negative impacts on Northbound US 17.

There will be no changes to traffic operations at intersections in the West Ashley area due to the proposed Build condition, other than minor changes at the Folly Road/Albemarle Road intersection which will still operate at acceptable levels of service in both 2015 (LOS B) and 2040 (LOS E).

Appendix B:

Model Calibration

Projected 2016 Volume

vph % GEHEBL 24 23 ‐1 ‐4.2% 0.2 +/‐ 100 vph Yes < 5 YesEBT 2091 2075 ‐16 ‐0.8% 0.4 +/‐ 15% Yes < 5 YesEBR 8 9 1 12.5% 0.3 +/‐ 100 vph Yes < 5 YesWBL 47 45 ‐2 ‐4.3% 0.3 +/‐ 100 vph Yes < 5 YesWBT 1761 1738 ‐23 ‐1.3% 0.5 +/‐ 15% Yes < 5 YesWBR 27 29 2 7.4% 0.4 +/‐ 100 vph Yes < 5 YesNBL 28 27 ‐1 ‐3.6% 0.2 +/‐ 100 vph Yes < 5 YesNBT 11 10 ‐1 ‐9.1% 0.3 +/‐ 100 vph Yes < 5 YesNBR 78 77 ‐1 ‐1.3% 0.1 +/‐ 100 vph Yes < 5 YesSBL 52 50 ‐2 ‐3.8% 0.3 +/‐ 100 vph Yes < 5 YesSBT 13 12 ‐1 ‐7.7% 0.3 +/‐ 100 vph Yes < 5 YesSBR 23 23 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesEBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBT 1832 1833 1 0.1% 0.0 +/‐ 15% Yes < 5 YesEBR 389 382 ‐7 ‐1.8% 0.4 +/‐ 100 vph Yes < 5 YesWBL 88 80 ‐8 ‐9.1% 0.9 +/‐ 100 vph Yes < 5 YesWBT 1277 1280 3 0.2% 0.1 +/‐ 15% Yes < 5 YesWBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBL 558 523 ‐35 ‐6.3% 1.5 +/‐ 100 vph Yes < 5 YesNBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBR 98 100 2 2.0% 0.2 +/‐ 100 vph Yes < 5 YesSBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBT 1536 1530 ‐6 ‐0.4% 0.2 +/‐ 15% Yes < 5 YesEBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBT 1161 1140 ‐21 ‐1.8% 0.6 +/‐ 15% Yes < 5 YesWBR 93 92 ‐1 ‐1.1% 0.1 +/‐ 100 vph Yes < 5 YesNBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBL 141 140 ‐1 ‐0.7% 0.1 +/‐ 100 vph Yes < 5 YesSBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBR 3 3 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesEBL 45 44 ‐1 ‐2.2% 0.1 +/‐ 100 vph Yes < 5 YesEBT 1632 1627 ‐5 ‐0.3% 0.1 +/‐ 15% Yes < 5 YesEBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBT 1217 1193 ‐24 ‐2.0% 0.7 +/‐ 15% Yes < 5 YesWBR 55 57 2 3.6% 0.3 +/‐ 100 vph Yes < 5 YesNBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBL 39 36 ‐3 ‐7.7% 0.5 +/‐ 100 vph Yes < 5 YesSBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBR 37 39 2 5.4% 0.3 +/‐ 100 vph Yes < 5 YesEBL 22 20 ‐2 ‐9.1% 0.4 +/‐ 100 vph Yes < 5 YesEBT 1540 1518 ‐22 ‐1.4% 0.6 +/‐ 15% Yes < 5 YesEBR 109 101 ‐8 ‐7.3% 0.8 +/‐ 100 vph Yes < 5 YesWBL 10 11 1 10.0% 0.3 +/‐ 100 vph Yes < 5 YesWBT 1171 1142 ‐29 ‐2.5% 0.9 +/‐ 15% Yes < 5 YesWBR 7 6 ‐1 ‐14.3% 0.4 +/‐ 100 vph Yes < 5 YesNBL 89 90 1 1.1% 0.1 +/‐ 100 vph Yes < 5 YesNBT 7 7 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesNBR 25 24 ‐1 ‐4.0% 0.2 +/‐ 100 vph Yes < 5 YesSBL 8 6 ‐2 ‐25.0% 0.8 +/‐ 100 vph Yes < 5 YesSBT 16 15 ‐1 ‐6.3% 0.3 +/‐ 100 vph Yes < 5 YesSBR 12 14 2 16.7% 0.6 +/‐ 100 vph Yes < 5 YesEBL 74 64 ‐10 ‐13.5% 1.2 +/‐ 100 vph Yes < 5 YesEBT 1239 1245 6 0.5% 0.2 +/‐ 15% Yes < 5 YesEBR 260 255 ‐5 ‐1.9% 0.3 +/‐ 100 vph Yes < 5 YesWBL 9 9 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesWBT 605 614 9 1.5% 0.4 +/‐ 100 vph Yes < 5 YesWBR 15 22 7 46.7% 1.6 +/‐ 100 vph Yes < 5 YesNBL 488 473 ‐15 ‐3.1% 0.7 +/‐ 100 vph Yes < 5 YesNBT 567 557 ‐10 ‐1.8% 0.4 +/‐ 100 vph Yes < 5 YesNBR 13 11 ‐2 ‐15.4% 0.6 +/‐ 100 vph Yes < 5 YesSBL 31 30 ‐1 ‐3.2% 0.2 +/‐ 100 vph Yes < 5 YesSBT 351 334 ‐17 ‐4.8% 0.9 +/‐ 100 vph Yes < 5 YesSBR 95 93 ‐2 ‐2.1% 0.2 +/‐ 100 vph Yes < 5 Yes

5 US 17 Stocker Drive

EB

WB

EB

SB

NB

EB

WB

WB

WB

SB

US 17

Meets? Measure Meets?Modeled Volume

(vph)Difference

Measure

Node # Primary Road Direction MovementSecondary Road

Field Balanced Volume(vph)

2 SC 61 Wesley Drive

NB

SB

3 US 17 Magnolia Road

4 US 17 Avondale Avenue

EB

NB

Wesley Drive

Ashley River ‐ AM Peak Hour VISSIM Volume Calibration

Calibrated Model ‐ VISSIM (Version 7.0)Volume Calibration

TargetsGEH Calibration Targets

1 SC 61 Riverdale Drive

EB

WB

NB

SB

NB

SB

EB

WB

NB

SB

6


vph % GEHMeets? Measure Meets?

Modeled Volume(vph)

DifferenceMeasure






EBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBL 631 631 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesWBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBR 19 3 ‐16 ‐84.2% 4.8 +/‐ 100 vph Yes < 5 YesNBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBT 1049 1030 ‐19 ‐1.8% 0.6 +/‐ 15% Yes < 5 YesNBR 1663 1635 ‐28 ‐1.7% 0.7 +/‐ 15% Yes < 5 YesSBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBT 620 596 ‐24 ‐3.9% 1.0 +/‐ 100 vph Yes < 5 YesSBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBL 249 246 ‐3 ‐1.2% 0.2 +/‐ 100 vph Yes < 5 YesEBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBR 168 170 2 1.2% 0.2 +/‐ 100 vph Yes < 5 YesWBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBL 97 96 ‐1 ‐1.0% 0.1 +/‐ 100 vph Yes < 5 YesNBT 2463 2422 ‐41 ‐1.7% 0.8 +/‐ 15% Yes < 5 YesNBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBT 1100 1082 ‐18 ‐1.6% 0.5 +/‐ 15% Yes < 5 YesSBR 151 143 ‐8 ‐5.3% 0.7 +/‐ 100 vph Yes < 5 YesEBL 5 5 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesEBT 4 4 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesEBR 46 45 ‐1 ‐2.2% 0.1 +/‐ 100 vph Yes < 5 YesWBL 11 10 ‐1 ‐9.1% 0.3 +/‐ 100 vph Yes < 5 YesWBT 2 2 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesWBR 42 41 ‐1 ‐2.4% 0.2 +/‐ 100 vph Yes < 5 YesNBL 48 43 ‐5 ‐10.4% 0.7 +/‐ 100 vph Yes < 5 YesNBT 2513 2485 ‐28 ‐1.1% 0.6 +/‐ 15% Yes < 5 YesNBR 2 2 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesSBL 28 28 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesSBT 1231 1208 ‐23 ‐1.9% 0.7 +/‐ 15% Yes < 5 YesSBR 9 8 ‐1 ‐11.1% 0.3 +/‐ 100 vph Yes < 5 YesEBL 23 23 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesEBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBR 2 1 ‐1 ‐50.0% 0.8 +/‐ 100 vph Yes < 5 YesWBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBT 2540 2513 ‐27 ‐1.1% 0.5 +/‐ 15% Yes < 5 YesNBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBT 1284 1258 ‐26 ‐2.0% 0.7 +/‐ 15% Yes < 5 YesSBR 4 5 1 25.0% 0.5 +/‐ 100 vph Yes < 5 YesEBL 1380 1345 ‐35 ‐2.5% 0.9 +/‐ 15% Yes < 5 YesEBT 7 7 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesEBR 2 0 ‐2 ‐100.0% 2.0 +/‐ 100 vph Yes < 5 YesWBL 6 6 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesWBT 5 4 ‐1 ‐20.0% 0.5 +/‐ 100 vph Yes < 5 YesWBR 14 14 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesNBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBT 1146 1151 5 0.4% 0.1 +/‐ 15% Yes < 5 YesNBR 11 12 1 9.1% 0.3 +/‐ 100 vph Yes < 5 YesSBL 26 22 ‐4 ‐15.4% 0.8 +/‐ 100 vph Yes < 5 YesSBT 523 516 ‐7 ‐1.3% 0.3 +/‐ 100 vph Yes < 5 YesSBR 737 724 ‐13 ‐1.8% 0.5 +/‐ 15% Yes < 5 YesEBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBT 1594 1552 ‐42 ‐2.6% 1.1 +/‐ 15% Yes < 5 YesEBR 69 69 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesWBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBL 88 87 ‐1 ‐1.1% 0.1 +/‐ 100 vph Yes < 5 YesNBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBR 227 226 ‐1 ‐0.4% 0.1 +/‐ 100 vph Yes < 5 YesSBL 2 4 2 100.0% 1.2 +/‐ 100 vph Yes < 5 YesSBT 154 148 ‐6 ‐3.9% 0.5 +/‐ 100 vph Yes < 5 YesSBR 562 543 ‐19 ‐3.4% 0.8 +/‐ 100 vph Yes < 5 Yes

7 Folly Road Wesley Drive

Maybank Highway

NB

SB

EB

WB

NB

SB

10 Folly Road Formosa Drive

NB

SB

9

EB

SB

Folly Road

8 Folly Road

Folly Road Yeamans Road

EB

SB

WB

NB

SB

Windermere Boulevard

WB

EB

WB

EB

WB

NB

EB

NB

12 Folly Road Albemarle Road

WB

11


vph % GEHMeets? Measure Meets?

Modeled Volume(vph)

DifferenceMeasure






EBL 414 395 ‐19 ‐4.6% 0.9 +/‐ 100 vph Yes < 5 YesEBT 350 347 ‐3 ‐0.9% 0.2 +/‐ 100 vph Yes < 5 YesEBR 759 735 ‐24 ‐3.2% 0.9 +/‐ 15% Yes < 5 YesWBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBR 182 180 ‐2 ‐1.1% 0.1 +/‐ 100 vph Yes < 5 YesNBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesNBT 905 899 ‐6 ‐0.7% 0.2 +/‐ 15% Yes < 5 YesNBR 54 56 2 3.7% 0.3 +/‐ 100 vph Yes < 5 YesSBL 104 104 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesSBT 811 795 ‐16 ‐2.0% 0.6 +/‐ 15% Yes < 5 YesSBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBT 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesEBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesWBL 711 702 ‐9 ‐1.3% 0.3 +/‐ 15% Yes < 5 YesWBT 107 107 0 0.0% 0.0 +/‐ 100 vph Yes < 5 YesWBR 109 106 ‐3 ‐2.8% 0.3 +/‐ 100 vph Yes < 5 YesNBL 628 629 1 0.2% 0.0 +/‐ 100 vph Yes < 5 YesNBT 873 843 ‐30 ‐3.4% 1.0 +/‐ 15% Yes < 5 YesNBR 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBL 0 0 0 NA 0.0 +/‐ 100 vph Yes < 5 YesSBT 204 198 ‐6 ‐2.9% 0.4 +/‐ 100 vph Yes < 5 YesSBR 157 160 3 1.9% 0.2 +/‐ 100 vph Yes < 5 Yes

14 Lockwood Drive Spring Street

EB

WB

NB

SB

13 Lockwood Drive Bee Street

EB

WB

NB

SB

2‐Hour 30‐MinUS 17 NB 94.8 103.8 105.0 113.0 10.2 9.2 10.8% 8.8%Bee St 185.8 235.0 200.1 222.3 14.3 ‐12.7 7.7% ‐5.4%Lockwood Dr SB 120.1 127.3 136.3 147.5 16.2 20.2 13.5% 15.9%Weighted Average 111.8 124.0 124.5 134.9 12.6 10.9 11.3% 8.8%US 17 NB 83.1 95.0 114.4 127.6 31.3 32.6 37.7% 34.3%Bee St 168.2 217.3 209.3 233.4 41.1 16.0 24.4% 7.4%Lockwood Dr SB 113.3 125.0 141.8 157.0 28.5 32.0 25.2% 25.6%Weighted Average 99.9 115.3 131.3 146.1 31.5 30.8 31.5% 26.7%US 17 NB 112.5 129.7 140.1 152.8 27.6 23.1 24.6% 17.8%Bee St 213.4 286.0 229.3 251.6 15.9 ‐34.4 7.4% ‐12.0%Lockwood Dr SB 127.4 142.7 146.2 157.1 18.8 14.4 14.8% 10.1%Weighted Average 121.4 143.2 147.8 161.3 26.4 18.0 21.8% 12.6%

All Roads (2016) Weighted Average 112.0 129.1 136.1 149.1 24.1 20.0 21.6% 15.5%

VISSIM 1 hr Avg

Field Averages 30‐Min Difference

2‐Hour Difference

Folly Rdat Wesley

Starting Point End PointVISSIM 30 Min Avg

SC 61

US 17

2‐Hour % Difference

30‐Min % Difference

Travel Time Calibration

Appendix C:

Signal Timings

Appendix D:

Existing Conditions (2016) Analysis

2016 Detailed AM Peak Hour Volume Summary

VISSIM VolumeAlternative Link # Name Run 1 Run 2 Run 3 Run 4 Run 5 Run 6 Run 7 Run 8 Run 9 Run 10 Avg

50 US 17 1,251 1,252 1,251 1,223 1,280 1,270 1,219 1,290 1,233 1,273 1,254 1,266 ‐1%72 SC 61 1,148 1,179 1,187 1,198 1,180 1,205 1,166 1,208 1,159 1,215 1,184 1,189 0%47 Folly Rd 1,798 1,751 1,752 1,765 1,743 1,777 1,772 1,716 1,772 1,729 1,758 1,823 ‐4%77 NB US 17 Bridge 4,228 4,194 4,222 4,234 4,235 4,252 4,206 4,238 4,187 4,237 4,223 4,278 ‐1%50 US 17 1,251 1,251 1,251 1,222 1,275 1,263 1,219 1,290 1,232 1,273 1,253 1,266 ‐1%72 SC 61 1,148 1,179 1,185 1,199 1,179 1,205 1,166 1,208 1,159 1,214 1,184 1,189 0%47 Folly Rd 1,797 1,747 1,747 1,765 1,719 1,782 1,772 1,718 1,770 1,728 1,754 1,823 ‐4%77 NB US 17 Bridge 4,232 4,193 4,217 4,235 4,193 4,265 4,204 4,234 4,174 4,234 4,218 4,278 ‐1%

Target Volume % Diff

2016 No Build (Existing Geometry + Ramp Improvements)

2028 Build (Off‐Ramp Improvements + 3‐Lane Section w/ Shared Use

Path)

2016 Link LOS Density Summary

2016 No Build (Off-Ramp Improvements Only; Existing Geometry)

Link Description Vol Density LOS47 Folly Road 1,758 28.3 C52 Folly Road 1,788 27.4 C48 US 17 1,238 37.5 E50 US 17 1,254 36.9 E74 US 17 1,268 25.9 C73 US 17 1,274 26.1 C41 US 17 1,281 21.0 C4 Merge of US 17 and Folly Road 3,026 31.4 D76 SC 61 Ramp 1,184 37.4 E72 SC 61 Ramp 1,184 37.1 E56 SC 61 Ramp 1,189 37.5 E55 SC 61 Ramp 1,186 38.1 E45 SC 61 Ramp 1,192 38.6 E44 SC 61 Ramp 1,219 36.5 E42 SC 61 Ramp 1,921 24.3 C7 Merge of US17/Folly Road and SC 61 4,203 33.0 D77 T. Allen Legare Bridge 4,223 26.5 C101 T. Allen Legare Bridge 4,180 28.7 C

Weighted Average 34,569 28.7 C

2016 Build (Off-Ramp Improvements + 3-Lane Section w/ Shared Use Path)

Link Description Vol Density LOS47 Folly Road 1,754 55.3 F52 Folly Road 1,783 55.6 F48 US 17 1,236 44.4 E50 US 17 1,253 38.4 E74 US 17 1,266 27.0 C73 US 17 1,272 26.7 C41 US 17 1,280 21.1 C4 Merge of US 17 and Folly Road 3,019 51.3 F76 SC 61 Ramp 1,184 38.5 E72 SC 61 Ramp 1,184 37.5 E56 SC 61 Ramp 1,189 37.5 E55 SC 61 Ramp 1,186 37.8 E45 SC 61 Ramp 1,192 38.3 E44 SC 61 Ramp 1,219 36.0 E42 SC 61 Ramp 1,921 24.2 C7 Merge of US17/Folly Road and SC 61 4,196 49.2 F77 T. Allen Legare Bridge 4,218 46.8 F101 T. Allen Legare Bridge 4,175 43.3 E

Weighted Average 34,527 44.9 E

Run 1 Run 2 Run 3 Run 4 Run 5 Run 6 Run 7 Run 8 Run 9 Run 10 AvgUS 17 NB 89.8 91.1 92.2 92.4 92.4 91.0 91.1 91.1 90.5 91.3 91.3Bee St 145.2 145.4 153.9 144.5 154.2 146.9 146.5 140.0 154.3 149.7 148.1Lockwood Dr SB 112.3 111.3 113.9 113.7 111.6 112.5 110.7 112.2 112.9 111.9 112.3Weighted Average 102.4 102.3 106.0 105.9 104.1 102.8 102.6 101.8 103.4 103.7 103.5US 17 NB 88.8 92.6 92.9 94.3 92.9 92.0 90.0 91.9 91.5 92.4 91.9Bee St 155.1 149.0 154.5 153.8 149.8 141.3 143.7 141.7 155.1 149.5 149.3Lockwood Dr SB 117.6 112.4 115.4 112.5 110.1 113.8 109.8 110.6 115.7 115.2 113.3Weighted Average 103.8 104.5 106.3 104.3 103.5 102.7 101.3 101.9 105.6 103.5 103.8US 17 NB 78.7 79.3 81.1 80.6 79.2 77.5 78.5 79.7 80.6 78.4 79.4Bee St 127.4 130.3 142.4 128.0 139.7 131.8 131.9 138.7 144.8 136.1 135.1Lockwood Dr SB 98.9 91.4 96.7 95.6 92.8 94.1 92.3 92.4 98.8 93.4 94.6Weighted Average 83.2 84.1 86.4 84.8 85.4 83.4 84.0 85.2 87.0 84.5 84.8US 17 NB 117.1 115.9 116.1 115.1 118.2 112.9 115.0 114.3 116.0 114.0 115.5Bee St 168.1 170.3 178.8 163.1 177.1 168.0 168.9 173.5 178.7 168.4 171.5Lockwood Dr SB 134.5 120.9 130.5 122.8 121.0 122.3 120.2 119.8 125.2 120.8 123.8Weighted Average 120.9 120.2 121.0 118.6 123.6 118.5 119.5 119.2 121.4 119.3 120.2

All Roads Weighted Average 110.7 110.3 112.1 110.5 112.1 109.3 109.4 108.7 111.7 109.9 110.5US 17 NB 101.8 95.9 94.2 95.6 116.2 94.6 96.0 109.8 97.4 102.7 100.4Bee St 167.3 154.2 147.8 154.0 184.3 154.9 155.9 179.7 170.3 169.9 163.8Lockwood Dr SB 123.1 118.9 121.2 120.5 144.4 121.6 123.5 142.1 124.6 129.6 126.9Weighted Average 114.6 108.4 108.7 111.1 131.7 108.4 110.8 126.3 112.7 118.4 115.1US 17 NB 107.0 104.0 103.2 105.8 152.0 101.9 102.6 135.8 105.4 110.0 112.8Bee St 162.7 160.8 166.0 167.8 215.9 154.6 165.4 189.5 171.2 175.8 173.0Lockwood Dr SB 134.1 125.8 128.4 125.6 174.4 130.0 130.8 165.2 129.3 138.5 138.2Weighted Average 120.1 116.6 117.5 116.5 164.5 114.7 117.5 149.0 119.8 123.2 126.0US 17 NB 103.2 98.6 95.9 97.5 148.8 96.3 97.8 140.5 100.3 108.1 108.7Bee St 153.3 145.7 156.3 146.7 221.9 152.7 159.9 197.9 160.3 176.1 167.1Lockwood Dr SB 121.0 113.3 113.1 120.8 170.8 118.4 127.5 172.7 128.4 140.0 132.6Weighted Average 107.6 103.2 101.0 102.3 156.7 102.5 104.8 146.6 107.0 115.6 114.7US 17 NB 162.1 164.5 154.3 152.0 238.7 150.1 157.3 217.0 159.5 161.3 171.7Bee St 217.5 215.3 220.9 207.5 317.5 207.0 229.9 273.8 222.6 226.2 233.8Lockwood Dr SB 175.1 165.9 163.3 170.2 244.1 166.4 184.2 259.1 171.9 180.6 188.1Weighted Average 165.9 168.5 159.4 156.4 245.8 156.0 164.0 222.4 165.2 167.7 177.1

All Roads Weighted Average 138.3 135.8 132.1 131.3 189.8 130.5 136.0 172.8 136.7 140.2 144.3

2016 VISSIM Travel Time Summary ‐ Peak 30 min

Alternative Starting Point End PointTravel Time (sec)

2016 No Build (Off‐Ramp Improvements Only; Existing

Geometry)

SC 61

US 17

Folly Rdat Albamarle

Folly Rdat Wesley

2028 Build (Off‐Ramp Improvements + 3‐Lane

Section w/ Shared Use Path)

SC 61

US 17


Folly Rdat Wesley

Appendix E:

Future Conditions (2028) Analysis

2028 Detailed AM Peak Hour Volume Summary

VISSIM VolumeAlternative Link # Name Run 1 Run 2 Run 3 Run 4 Run 5 Run 6 Run 7 Run 8 Run 9 Run 10 Avg

50 US 17 1,425 1,437 1,428 1,395 1,466 1,441 1,416 1,466 1,421 1,447 1,434 1,388 3%72 SC 61 1,266 1,292 1,307 1,290 1,285 1,316 1,284 1,311 1,272 1,321 1,294 1,303 ‐1%47 Folly Rd 1,944 1,904 1,873 1,881 1,883 1,881 1,888 1,853 1,916 1,880 1,890 1,998 ‐5%77 NB US 17 Bridge 4,674 4,648 4,634 4,609 4,671 4,675 4,609 4,671 4,627 4,665 4,648 4,689 ‐1%50 US 17 1,425 1,363 1,363 1,394 1,462 1,443 1,415 1,468 1,416 1,448 1,420 1,388 2%72 SC 61 1,263 1,293 1,305 1,287 1,285 1,318 1,284 1,312 1,267 1,321 1,294 1,303 ‐1%47 Folly Rd 1,863 1,782 1,661 1,828 1,817 1,856 1,852 1,741 1,703 1,851 1,795 1,998 ‐10%77 NB US 17 Bridge 4,588 4,243 4,282 4,558 4,578 4,657 4,576 4,529 4,354 4,651 4,502 4,689 ‐4%

2028 No Build (Existing Geometry + Ramp Improvements)

2028 Build (Off‐Ramp Improvements + 3‐Lane Section w/ Shared Use

Path)

Target Volume % Diff

2028 Link LOS Density Summary

2028 No Build (Off-Ramp Improvements Only; Existing Geometry)

Link Description Vol Density LOS47 Folly Road 1,890 30.6 D52 Folly Road 1,916 29.5 D48 US 17 1,424 43.6 E50 US 17 1,434 45.5 F74 US 17 1,444 30.0 D73 US 17 1,451 29.5 D41 US 17 1,461 24.3 C4 Merge of US 17 and Folly Road 3,336 35.2 D76 SC 61 Ramp 1,295 41.2 E72 SC 61 Ramp 1,294 40.8 E56 SC 61 Ramp 1,299 41.5 E55 SC 61 Ramp 1,296 42.4 E45 SC 61 Ramp 1,302 42.9 E44 SC 61 Ramp 1,334 41.1 E42 SC 61 Ramp 2,110 27.3 C7 Merge of US17/Folly Road and SC 61 4,623 37.1 E77 T. Allen Legare Bridge 4,648 31.0 D101 T. Allen Legare Bridge 4,599 31.9 D

Weighted Average 38,156 32.8 D

2028 Build (Off-Ramp Improvements + 3-Lane Section w/ Shared Use Path)

Link Description Vol Density LOS47 Folly Road 1,795 66.1 F52 Folly Road 1,814 70.5 F48 US 17 1,406 68.8 F50 US 17 1,420 64.9 F74 US 17 1,435 46.6 F73 US 17 1,445 43.6 E41 US 17 1,458 31.3 D4 Merge of US 17 and Folly Road 3,214 69.5 F76 SC 61 Ramp 1,293 46.3 F72 SC 61 Ramp 1,294 41.9 E56 SC 61 Ramp 1,298 41.7 E55 SC 61 Ramp 1,295 42.4 E45 SC 61 Ramp 1,301 42.9 E44 SC 61 Ramp 1,332 41.2 E42 SC 61 Ramp 2,107 27.3 C7 Merge of US17/Folly Road and SC 61 4,495 62.4 F77 T. Allen Legare Bridge 4,502 61.5 F101 T. Allen Legare Bridge 4,467 55.9 F

Weighted Average 58.6 F

Run 1 Run 2 Run 3 Run 4 Run 5 Run 6 Run 7 Run 8 Run 9 Run 10 AvgUS 17 NB 92.7 94.2 92.5 95.5 92.5 93.1 93.9 96.8 97.9 96.0 94.5Bee St 143.4 144.7 145.0 146.4 154.8 157.0 150.0 152.5 147.7 151.4 149.3Lockwood Dr SB 115.5 114.7 112.7 118.0 112.8 113.1 117.9 117.6 114.8 116.5 115.4Weighted Average 105.2 105.6 105.2 108.6 105.3 104.7 107.1 108.3 108.2 107.9 106.6US 17 NB 96.5 96.0 98.3 99.8 97.2 97.4 99.3 101.8 102.0 102.2 99.0Bee St 147.0 160.7 143.7 151.8 148.7 148.3 155.5 155.5 156.2 143.5 151.1Lockwood Dr SB 121.9 118.6 114.8 120.3 114.8 119.5 125.0 119.5 114.5 121.8 119.1Weighted Average 106.4 107.2 105.6 108.8 105.8 106.2 110.0 110.4 109.6 109.5 108.0US 17 NB 81.9 80.8 83.5 82.8 81.6 80.3 82.3 85.0 84.2 84.4 82.7Bee St 133.8 138.2 133.8 133.9 145.1 133.2 136.4 144.9 136.1 134.5 137.0Lockwood Dr SB 106.5 95.9 93.3 102.0 94.6 93.1 104.3 100.5 95.4 98.8 98.4Weighted Average 87.3 86.4 87.7 87.5 87.9 85.8 88.3 90.5 89.0 89.0 87.9US 17 NB 129.6 124.3 128.5 127.8 128.9 126.2 128.5 128.7 131.3 132.5 128.6Bee St 181.8 182.5 176.6 177.3 197.1 176.5 185.0 186.9 181.5 186.3 183.1Lockwood Dr SB 136.0 122.5 127.7 136.8 130.7 122.7 136.0 134.7 131.1 132.7 131.1Weighted Average 133.6 128.7 132.1 131.6 135.0 130.9 133.5 133.6 135.5 136.8 133.1

All Roads Weighted Average 117.3 115.4 115.8 117.7 117.6 115.8 118.8 118.8 119.7 119.9 117.7US 17 NB 116.2 146.8 142.7 132.3 117.8 103.1 102.1 140.4 144.5 106.3 125.2Bee St 172.4 208.4 206.3 203.8 183.4 167.9 166.0 189.5 205.9 167.2 187.1Lockwood Dr SB 143.8 179.8 178.2 159.6 146.3 128.5 130.5 158.8 172.1 127.6 152.5Weighted Average 130.7 163.4 161.3 149.2 133.6 116.6 117.6 150.5 159.5 119.0 140.1US 17 NB 132.5 180.4 323.7 212.9 144.3 118.4 115.0 235.8 241.9 119.5 182.4Bee St 197.9 218.4 378.3 265.6 204.2 176.7 184.5 295.4 287.9 174.3 238.3Lockwood Dr SB 161.2 192.4 368.7 241.0 170.4 138.3 141.1 252.8 278.4 139.8 208.4Weighted Average 144.2 186.6 338.2 223.4 155.5 127.3 127.0 244.8 255.7 128.2 193.0US 17 NB 133.9 166.6 293.1 179.4 148.7 111.6 112.0 210.7 240.2 111.4 170.8Bee St 183.4 214.9 389.4 220.9 216.3 166.9 169.2 286.2 293.1 173.6 231.4Lockwood Dr SB 161.4 165.3 340.0 198.2 168.8 138.0 135.3 253.5 285.0 130.9 197.7Weighted Average 139.1 171.0 302.2 183.3 155.9 118.0 118.5 218.7 247.0 117.3 177.1US 17 NB 212.4 237.5 426.2 274.4 238.0 191.5 185.7 316.9 355.5 176.0 261.4Bee St 257.8 272.7 508.5 315.9 303.5 249.2 244.2 381.2 396.4 241.8 317.1Lockwood Dr SB 229.5 242.9 443.4 326.5 255.5 199.6 205.8 339.4 430.4 184.8 285.8Weighted Average 215.9 240.4 432.5 278.5 244.4 197.3 191.3 322.4 361.1 181.7 266.5

All Roads Weighted Average 168.7 199.4 317.0 224.1 184.5 152.1 150.7 246.1 264.5 146.4 206.1

2028 VISSIM Travel Time Summary ‐ Peak 30 min

Alternative Starting Point End PointTravel Time (sec)

2028 Build (Off‐Ramp Improvements + 3‐Lane

Section w/ Shared Use Path)

SC 61

US 17


Folly Rdat Wesley

2028 No Build (Off‐Ramp Improvements Only; Existing

Geometry)

SC 61

US 17


Folly Rdat Wesley

Year AlternativeAverage Density (veh/ln/mi)

% Change from 2016 NB w Ramp

Speed (mph) on Bridge

% Change from 2016 NB w Ramp

LOS

No Build (Existing with Ramp Improvements)

28.7 0% 33.4 0% C

Build Test 2 44.9 57% 30.5 ‐9% E

No Build (Existing with Ramp Improvements)

32.8 14% 32.6 ‐2% D

Build Test 2 58.6 104% 25.9 ‐22% F

Density Summary

2028

2016

US 17 NB 91.3 100.4 94.5 125.2 9.1 3.2 33.9 30.7 10.0% 3.5% 37.2% 32.5%Bee St 148.1 163.8 149.3 187.1 15.8 1.2 39.0 37.8 10.6% 0.8% 26.4% 25.3%Lockwood Dr SB 112.3 126.9 115.4 152.5 14.7 3.1 40.2 37.1 13.0% 2.7% 35.8% 32.2%Weighted Average 103.5 115.1 106.6 140.1 11.6 3.1 36.6 33.5 11.2% 3.0% 35.3% 31.4%US 17 NB 91.9 112.8 99.0 182.4 20.8 7.1 90.5 83.4 22.7% 7.7% 98.4% 84.2%Bee St 149.3 173.0 151.1 238.3 23.6 1.7 89.0 87.2 15.8% 1.2% 59.6% 57.7%Lockwood Dr SB 113.3 138.2 119.1 208.4 24.9 5.8 95.1 89.3 22.0% 5.1% 83.9% 75.0%Weighted Average 103.8 126.0 108.0 193.0 22.2 4.2 89.3 85.1 21.4% 4.1% 86.1% 78.8%US 17 NB 115.5 171.7 128.6 261.4 56.2 13.2 145.9 132.8 48.7% 11.4% 126.4% 103.2%Bee St 171.5 233.8 183.1 317.1 62.3 11.7 145.6 134.0 36.3% 6.8% 84.9% 73.1%Lockwood Dr SB 123.8 188.1 131.1 285.8 64.3 7.3 162.0 154.7 51.9% 5.9% 130.8% 118.0%Weighted Average 120.2 177.1 133.1 266.5 56.9 12.9 146.3 133.4 47.3% 10.7% 121.7% 100.3%

All Roads Weighted Average 110.5 144.3 117.7 206.1 33.9 7.2 95.6 88.4 30.7% 6.5% 86.6% 75.2%

2016 NB w Ramp to 2028

NB

No Build (Existing with Ramp

Improvements)Build Test 2

2016 Travel Times (Sec) 2028 Travel Times (Sec) Total Travel Time Change (Sec)2016 NB w

Ramp to 2016 Build Test 2

Travel Time Summary

Folly Rdat Wesley

Starting Point End Point 2016 NB w Ramp to 2028

Test 2

2028 NB to 2028 Build

US 17

2016 NB w Ramp to 2028 Build Test 2

2028 NB to 2028 Build


NB

No Build (Existing with Ramp

Improvements)

Build Test 2

SC 61


Test 2

Travel Time Percent Change

Ashley River Bridge Traffic Study€¦ · Appendix A. 2015 Ashley River Bridge Traffic Study Update...

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