Appendix D Traffic Data and Reports.pdf

Appendix D

Traffic Data and Reports

GWMP_ VA 123 Interchange Modification Report-IMR (2017) Conditional IMR Approval for VA Route 123 (2018)

GWMP Traffic Data Report (2004) Travel Forecasting/Diversion Analysis Report (2017)

George Washington Memorial Parkway Virginia Route 123 Interchange Modification Report

Prepared for: Eastern Federal Lands Highway Division, Federal Highway Administration

Prepared by: Sabra, Wang & Associates, Inc.

Date: October 30, 2017

GWMP at Virginia Route 123 Interchange June 2017 Interchange Modification Report Page 1

George Washington Memorial Parkway/Route 123 Interchange Modification Report

Table of Contents

EXECUTIVE SUMMARY

1. INTRODUCTION

1.1. Background

1.2. Project Purpose

1.3. Project Location

2. METHODOLOGY

2.1. Related Studies

2.2. Key Assumptions

2.3. Traffic Analysis Methodology

3. EXISTING CONDITIONS

3.1. Demographics

3.2. Existing Land Use

3.3. Existing Roadway Network

3.4. Alternative Travel Modes

3.5. Interchanges

3.6. Existing Data

3.7. Operational Performance

3.7.1. Base Model Development and Calibration

3.7.2. GWMP Mainline Operations

3.7.3. Virginia Route 123 Intersection Analysis

3.8. Existing Safety Conditions

3.8.1. Crash Summary and History

3.8.2. Crash Rates

3.8.3. Crash Locations

3.8.4. Crash Type

3.8.5. Crash Severity

3.9. Existing Environmental Constraints

4. ALTERNATIVES CONSIDERED

4.1. No Build Alternative

4.2. Build Alternatives

4.2.1. Alternative 4

4.2.2. Alternative 5

4.3. Selection of Preferred Alternative

5. ROADWAY GEOMETRY

5.1. Design / Geometric Criteria

5.2. Waivers / Exceptions

5.3. Conceptual Design Plans and Typical Sections

6. TRAFFIC DATA

6.1. Background

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6.2. Traffic Data Collection

6.2.1. Daily Volume Counts

6.2.2. Intersection Turning Movement Counts

6.3. 2017 Existing Volume Network

6.4. Development of Future Traffic Forecasts

6.4.1. Future No Build / Build Forecasts

7. TRAFFIC ANALYSIS

7.1. Future Traffic Operations

7.1.1. Analysis of 2025 No-Build Conditions

7.1.2. Analysis of 2025 Build Conditions

7.2. Summary of Operational Analysis

7.3. Crash Data and Analysis

7.3.1. No Build Crash Analysis

7.3.2. Future Build Crash Analysis

8. LAND USE

8.1. Local Land Use and Status

8.2. Future Planned Development

9. ENVIRONMENTAL COMPLIANCE

Appendices

Appendix A: Alternative 4 Conceptual Design Plans Appendix B: Peak Hour Volumes Appendix C: VISSIM Freeway Schematics Appendix D: Capacity Analysis Results

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EXECUTIVE SUMMARY

The National Park Service (NPS) of the U.S. Department of the Interior (DOI) has identified a need for improvements to the George Washington Memorial Parkway (GWMP) between Interstate 495 and Spout Run Parkway. At the NPS’s request, the Eastern Federal Lands Highway Division (EFLHD) of the Federal Highway Administration (FHWA) performed planning and engineering studies to determine the best approach to rehabilitate the deteriorating mainline roadway pavement in northern section of the GWMP from Spout Run to I-495. In association with this larger scale rehabilitation project, this Interchange Modification Report (IMR) assesses the operational and safety impacts of the proposed modifications to the GWMP interchange with Virginia State Route 123. Upon receipt of Virginia Department of Transportation (VDOT) approval of this IMR, it is NPS’s intent to proceed with the final design and construction of the interchange modifications.

The primary purpose of this project is to address existing and future safety and operational concerns at the interchange. The proposed improvements are focused on increasing safety at the interchange, particularly for the ramps on the west side of the interchange which provide the connections to and from the southbound GWMP mainline travel lanes. Changes to lane configuration, ramp geometry including elimination of a loop ramp, as well as improvements to acceleration/deceleration lanes would be made to allow for smoother merging and diverging. The proposed improvements will also facilitate improved safety and traffic flow along southbound GWMP. While the proposed changes may affect operations in the vicinity of the interchange, they are not intended to add any additional capacity in the form of additional through lanes, ramps, acceleration/deceleration lanes, etc. Other improvements at the interchange will address drainage, signing, pavement markings, curb and gutter, and rehabilitation/resurfacing of existing ramps on the east side of the interchange which connect Route 123 to the northbound GWMP mainline.

The existing safety and operational concerns include the following:

1. In order to accommodate a free-flow condition for the eastbound Route 123 to southbound GWMP ramp, the two southbound lanes of GWMP merge into one lane just upstream of the eastbound-to-southbound ramp gore. During peak periods, the reduction in the number of southbound through lanes at the interchange causes congestion along the southbound GWMP mainline.

2. The weaving segment between the two loop ramps is a problem area along the southbound lanes of the GWMP. The distance between the gore points at these ramps is less than 450 feet.

If the average travel speeds in the southbound direction are close to the posted speed of 50 mph, vehicles attempting to exit on or off at the interchange encounter problems with the large speed differentials.

3. The proximity of the southbound GWMP off-ramp tie-in point on Route 123 to the Kirby Road intersection hampers traffic attempting to enter Route 123 from the off-ramp due to traffic queuing at the signalized intersection of Route 123 at Kirby Road.

Of the total 77 reported crashes within the study area over the past five years, 31 occurred along the Virginia Route 123 and GWMP mainline travel lanes in the vicinity of the interchange.

The criteria and process used to identify the Preferred Build Alternative are detailed in Chapter 4 of this IMR. The selection criteria included traffic operations and safety. Five alternatives were originally

Interchange Modification Report Page 4 developed for the GWMP / Route 123 (Chain Bridge Road/Dolley Madison Boulevard) interchange as part of the George Washington Memorial Parkway North Section Improvements Candidate Alternatives Report of which two (Alternative 4 and Alternative 5) were evaluated in greater detail as part of this study. Ultimately, these findings led to the development of the Preferred Alternative, Alternative 4 Modified. Alternative 4 Modified would provide improved safety and traffic operations compared to the No Build Alternative.

Future year traffic forecasts were generated for Opening Year 2025. Since the proposed improvements are not expected to substantially impact regional traffic patterns, one set of forecasts was developed for each time period and the same forecasts were applied to both the Build and No Build scenarios. Future year traffic forecasts were developed by estimating a linear growth rate between Existing Year (2017) and Opening Year (2025). The most recent MWCOG models (Version 2.3.66) for Existing (2017) and Opening Year (2025) were run and output ADTs were compared to calculate the annual growth percentage. Full details regarding the development of the future traffic forecasts for this study are provided in Chapter 6.

The Opening Year No Build and Build scenarios were analyzed using the methodologies in the 2016 edition of the Highway Capacity Manual (HCM6). Analyses were conducted using the HCS7 and Synchro software packages. These analyses were conducted for the mainline GWMP freeway segments, weaving segments, and ramp junctions (merge and diverge areas); analyses were also conducted for five intersections along Route 123, including the GWMP ramp terminals. Supplemental analyses were conducted for the entire study area using VISSIM. Details on the selection of the traffic analysis tools used in the analysis are provided in Chapter 2.

Operational analyses were conducted for Opening Year (2025) No Build and Opening Year (2025) Build conditions. Full details regarding the existing and future year operational analyses are documented in Chapter 3 and Chapter 7.

The operational analyses conducted for this IMR indicate that the Preferred Alternative 4 Modified design will provide improved operations along the GWMP southbound mainline travel lanes at the Virginia Route 123 interchange relative to the No-Build Alternative. Significant reductions in peak period congestion levels are expected in the southbound direction along the GWMP due to the elimination of the existing mainline lane drop through the interchange, while ramp modifications aimed at improving safety do not result in any adverse operational impacts on GWMP. Furthermore, the interchange modifications, including the proposed half signal on Route 123 at the southbound ramps entry points, will not result in additional congestion or major delays along Virginia Route 123.

A qualitative assessment of the future safety performance of the GWMP / Route 123 (Chain Bridge Road/Dolley Madison Boulevard) interchange was conducted to determine any safety-related impacts of the proposed roadway improvements. If no improvements are made at the interchange (No-Build), it is reasonable to assume that the existing crash patterns would be unlikely to change substantially and the number of collisions would increase as volumes increase.

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The expected impacts of Alternative 4 Modified are as follows:

• It would be expected that the number of rear-end and sideswipe crashes would be reduced in the southbound direction on the GWMP and the westbound direction of Route 123 due to the elimination of the existing weaving segments. Those crash types are common in weaving segments.

• Rear-end crashes would be reduced in the southbound direction on the GWMP, because the lane drop which causes recurring congestion would be removed. The reduction of crashes upstream of the interchange may be somewhat negated by creating a merging condition (rather than an additional travel lane) for the Route 123 eastbound to GWMP southbound ramp at the southern end of the interchange which may increase rear end and sideswipe crashes.

• It would be expected that sideswipe crashes in the westbound direction east of the Route 123 at Kirby Road intersection would be reduced by relocating the ramp from southbound GWMP to westbound Route 123. Alternative 4 Modified would increase the distance between the ramp tie-in point and the Kirby Road intersection, making it easier to make the maneuver to turn left at Kirby Road from Route 123. However, the addition of a new traffic signal (half signal) on Route 123 as part of Alternative 5 could lead to more rear end crashes.

FHWA Eight Policy Points Summary

The following section of the report outlines the eight (8) policy requirements associated with the conduct of interchange modification studies listed in the Federal Register (Vol. 74, August 27, 2009) as they apply to the GWMP / Route 123 (Chain Bridge Road/Dolley Madison Boulevard) interchange.

1. Need for the Access Point Revision

The need being addressed by the request cannot be adequately satisfied by existing interchanges to the Interstate, and/or local roads and streets in the corridor can neither provide the desired access, nor can they be reasonably improved (such as access control along surface streets, improving traffic control, modifying ramp terminals and intersections, adding turn bays or lengthening storage) to satisfactorily accommodate the design-year traffic demands (23 CFR 625.2(a)).

The primary purpose of this project is to address existing and future safety and operational concerns at the interchange. The proposed improvements are focused on increasing safety at the interchange, particularly for the ramps on the west side of the interchange. The previously identified Preferred Alternative was devised to improve upon the problematic operations associated with the tight radii of the on- and off-ramps, the substandard acceleration/deceleration lanes, the inadequate weaving between the two loop ramps, and the poor operating conditions at the intersection of GWMP off-ramp at Kirby Road. The proposed improvements will also facilitate improved safety and flow along the southbound GWMP mainline travel lanes.

2. Reasonable Alternatives

The need being addressed by the request cannot be adequately satisfied by reasonable transportation system management (such as ramp metering, mass transit, and HOV facilities), geometric design, and alternative improvements to the Interstate without the proposed change(s) in access (23 CFR 625.2(a)).

Alternative 4 and Alternative 5 from the “George Washington Memorial Parkway North Section Improvements (from Spout Run Parkway to I-495): Candidate Alternatives Report” were preliminarily analyzed prior to developing Alternative 4 Modified, the Preferred Alternative. Alternative 4 Modified

Interchange Modification Report Page 6 was compared to the No Build condition and will perform as well or better than the No Build condition in terms of operations and safety.

The primary purpose of this project as stated in Policy Point 1 is to address safety concerns. The safety concerns cannot be addressed without reconfiguring the ramps on the west side of the interchange. It should be noted that the ramp reconfigurations do not add/remove any existing movements to/from GWMP from/to Route 123. In fact, all merge/diverge access points on the GWMP remain in the same location except for the loop ramp for westbound Route 123 to southbound GWMP which is removed and consolidated with the eastbound Route 123 to southbound GWMP on ramp.

3. Operational and Collision Analysis

An operational and safety analysis has concluded that the proposed change in access does not have a significant adverse impact on the safety and operation of the Interstate facility (which includes mainline lanes, existing, new, or modified ramps, ramp intersections with crossroad) or on the local street network based on both the current and the planned future traffic projections. The analysis shall, particularly in urbanized areas, include at least the first adjacent existing or proposed interchange on either side of the proposed change in access (23 CFR 625.2(a), 655.603(d) and 771.111(f)). The crossroads and the local street network, to at least the first major intersection on either side of the proposed change in access, shall be included in this analysis to the extent necessary to fully evaluate the safety and operational impacts that the proposed change in access and other transportation improvements may have on the local street network (23 CFR 625.2(a) and 655.603(d)). Requests for a proposed change in access must include a description and assessment of the impacts and ability of the proposed changes to safely and efficiently collect, distribute and accommodate traffic on the Interstate facility, ramps, intersection of ramps with crossroad, and local street network (23 CFR 625.2(a) and 655.603(d)). Each request must also include a conceptual plan of the type and location of signs proposed to support each design alternative (23 U.S.C. 109(d) and 23 CFR 655.603(d)).

Operational analyses were conducted for Opening Year (2025) No Build and Opening Year (2025) Build conditions.

The operational analyses conducted for this IMR indicate that the Preferred Alternative 4 Modified design will provide improved operations along GWMP southbound at the Virginia Route 123 interchange relative to the No-Build Alternative. Significant reductions in congestion are expected in southbound direction of GWMP due to the elimination of the existing mainline lane drop through the interchange, while ramp modifications aimed at improving safety do not result in any adverse operational impacts on the GWMP mainline movements. Furthermore, the interchange modifications, including the proposed half signal on Route 123 at the southbound ramps, will not result in additional congestion or major delays along Virginia Route 123.

A qualitative assessment of the future safety performance of the GWMP / Route 123 (Chain Bridge Road/Dolley Madison Boulevard) interchange was conducted to determine any safety-related impacts of the proposed roadway improvements. If no improvements are made at the interchange (No-Build), it is reasonable to assume that the existing crash patterns would be unlikely to change substantially and the number of collisions would increase as volumes increase.

The expected impacts of Alternative 4 Modified are as follows:

• It would be expected that the number of rear-end and sideswipe crashes would be reduced in the southbound direction on the GWMP and the westbound direction on Route 123 due to the elimination of the existing weaving segments. Those crash types are common in weaving segments.

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• Rear-end crashes would be reduced in the southbound direction on the GWMP, because the lane drop which causes recurring congestion would be removed. The reduction of crashes upstream of the interchange may be somewhat negated by creating a merging condition (rather than an add lane) for the Route 123 eastbound to GWMP southbound ramp at the southern end of the interchange which may increase rear end and sideswipe crashes.

• It would be expected that sideswipe crashes in the westbound direction east of the Route 123 at Kirby Road intersection would be reduced by relocating the ramp from southbound GWMP to westbound Route 123. Alternative 4 Modified would increase the distance between the ramp tie-in point and the Kirby Road intersection, making it easier to make the maneuver to turn left at Kirby Road.

However, the addition of a new traffic signal (half signal) on Route 123 as part of Alternative 5 could potentially lead to more rear end crashes.

4. Access Connections and Design

The proposed access connects to a public road only and will provide for all traffic movements. Less than “full interchanges” may be considered on a case-by-case basis for applications requiring special access for managed lanes (e.g. transit, HOVs, HOT lanes) or park and ride lots. The proposed access will be designed to meet or exceed current standards (23 CFR 625.2(a), 625.4(a)(2), and 655.603(d)).

The existing GWMP / Route 123 (Chain Bridge Road/Dolley Madison Boulevard) interchange provides for all traffic movements between GWMP and Route 123 and will continue to do so under the Preferred Alternative. The interchange will connect the GWMP, a public road maintained by NPS, to Route 123, a public road maintained by VDOT. The proposed improvements are being designed to satisfy all relevant AASHTO and VDOT design criteria.

5. Land Use and Transportation Plans

The proposal considers and is consistent with local and regional land use and transportation plans. Prior to receiving final approval, all requests for new or revised access must be included in an adopted Metropolitan Transportation Plan, in the adopted Statewide or Metropolitan Transportation Improvement Program (STIP or TIP), and the Congestion Management Process within transportation management areas, as appropriate, and as specified in 23 CFR part 450, and the transportation conformity requirements of 40 CFR parts 51 and 93.

The Preferred Alternative is congruent with existing land uses and transportation plans for the Northern Virginia portion of the Washington DC Metropolitan Region. Local and regional growth was determined from the most recent version of the MWCOG regional travel demand forecasting model.

6. Future Interchanges

In corridors where the potential exists for future multiple interchange additions, a comprehensive corridor or network study must accompany all requests for new or revised access with recommendations that address all of the proposed and desired access changes within the context of a longer-range system or network plan (23 U.S.C. 109(d), 23 CFR 625.2(a), 655.603(d), and 771.111).

Currently, no additional interchange additions or modifications have been proposed along the study segment of the GWMP between the Capital Beltway (I-495) and the Spout Run Parkway interchanges.

7. Coordination

When a new or revised access point is due to a new, expanded, or substantial change in current or planned future development or land use, requests must demonstrate appropriate coordination has occurred between the development and any proposed transportation system improvements (23 CFR 625.2(a) and 655.603 (d)).

The request must describe the commitments agreed upon to assure adequate collection and dispersion of the

Interchange Modification Report Page 8 traffic resulting from the development with the adjoining local street network and Interstate access point (23 CFR 625.2(a) and 655.603 (d)).

The primary purpose of this project is to address existing and future safety and operational concerns at the interchange, not to increase capacity due to expected future development or changes to land use.

Coordination, with localities, specifically, Fairfax and Arlington Counties, Virginia will be organized as needed.

8. Environmental Process

The proposal can be expected to be included as an alternative in the required environmental evaluation, review and processing. The proposal should include supporting information and current status of the environmental processing (23 CFR 771.111).

NEPA requirements will be met for this project. Preparation of an environmental assessment (EA) is currently underway.

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1. INTRODUCTION

1.1. Background

The National Park Service (NPS) of the U.S. Department of the Interior (DOI) has identified a need for improvements to the George Washington Memorial Parkway (GWMP) between Interstate 495 and Spout Run Parkway. At the NPS’s request, the Eastern Federal Lands Highway Division (EFLHD) of the Federal Highway Administration (FHWA) performed planning and engineering studies to determine the best approach to rehabilitate the deteriorating northern section of the GWMP from Spout Run to I-495.

In April 2004, a Design Scoping Report, GWMP North Design for George Washington Memorial Parkway, Arlington County and Fairfax County, Virginia, was developed jointly by NPS and FHWA to determine what the improvement project should include. In February 2006, the George Washington Memorial Parkway North Section Improvements Candidate Alternatives Report was released, which documented the process, information, and analysis the project team used to develop alternative concepts to rehabilitate the North Section of the GWMP. A critical part of the improvement project involves rehabilitating and reconstructing the GWMP interchange with Virginia Route 123 (Chain Bridge Road/Dolley Madison Boulevard). The Candidate Alternatives Report outlines several alternative concepts for this interchange.

This Interchange Modification Report (IMR) assesses the operational and safety impacts of the proposed modifications to the GWMP interchange with Route 123. Upon receipt of VDOT approval of this IMR, it is NPS’s intent to proceed with the final design and construction of the interchange modifications.

Opening year is currently anticipated to be in 2025. Preparation of an environmental assessment (EA) is currently underway.

1.2. Project Purpose

The primary purpose of this project is to address existing and future safety and operational concerns at the interchange. The proposed improvements are focused on increasing safety at this interchange, particularly for the ramps on the west side of the interchange that connect traffic movements on Route 123 to and from southbound GWMP mainline. Changes to acceleration/deceleration lanes will be made to allow for smoother merging and diverging. The proposed improvements will also facilitate improved safety and flow along southbound GWMP. While the proposed changes may affect operations in the vicinity of the interchange, they are not intended to add any additional capacity in the form of additional through lanes, ramps, acceleration/deceleration lanes, etc. Other improvements at the interchange will address drainage, signing, pavement markings, curb and gutter, and rehabilitation/resurfacing of existing ramps on the east side of the interchange which connect Route 123 to the GWMP northbound mainline.

Several specific safety issues have been identified by NPS/FHWA:

1. In order to accommodate a free-flow condition for the eastbound Route 123 to southbound GWMP ramp, the two southbound lanes of GWMP merge into one lane just upstream of eastbound-to-southbound ramp terminal. During peak periods, the reduction in the number of

Interchange Modification Report Page 10 available southbound through lanes at the interchange causes congestion along the southbound GWMP mainline.

2. The weaving segment between the two loop ramps is a problem area along the southbound lanes of the GWMP. The distance between the gore points at these ramps is less than 450 feet.

If the average travel speeds in the southbound direction are close to the posted speed limit of 50mph, vehicles attempting to exit on or off at the interchange encounter problems with the large speed differentials.

3. The proximity of the southbound GWMP off-ramp tie-in point on Route 123 to the Kirby Road intersection hampers traffic attempting to enter Route 123 from the off-ramp due to traffic queuing at the signalized intersection of Route 123 at Kirby Road.

The alternatives under consideration will be analyzed for safety implications and traffic operations as part of this study.

1.3. Project Location

The GWMP interchange with Route 123 is located in the McLean area of Fairfax County, Virginia. Route 123 runs through the center of Fairfax County in a crescent shape, connecting a number of the most urbanized areas in the County. Route 123 (Chain Bridge Road/Dolley Madison Boulevard) crosses the GWMP at a point approximately halfway between the Capital Beltway and the merge with Spout Run Parkway. For the purposes of this IMR, the GWMP is assumed to run in a north-south direction and Route 123 is assumed to run in an east-west direction.

The Study Area for this IMR includes the following roadway segments:

• George Washington Memorial Parkway: From south of the Spout Run Parkway merge/diverge to north of the CIA interchange

• Virginia Route 123 (Chain Bridge Road/Dolley Madison Boulevard): From west of Merchant Lane/Savile Lane to east of Crest Lane/McCay Lane

Figure 1-1 shows a map of the Study Area, which is comprised primarily of residential land along Route 123 and primarily wooded park land along the GWMP.

GWMP at Virginia Route 123 Interchange April 2017 Interchange Modification Report Page 11

Figure 1-1: Study Area

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2. METHODOLOGY

This Interchange Modification Report (IMR) was developed following the applicable VDOT and FHWA criteria. This request adheres to the regulations and guidance provided in the August 31, 2010, FHWA “Interstate System Access Information Guide” and addresses the eight (8) policy points detailed in the August 27, 2009, update to the Federal Register. Additionally, this request follows the organizational structure identified in the VDOT Location and Design Division’s Instructional and Informational Memorandum (IIM-LD-200.9) Interstate, NHS Non-Interstate and Non-NHS (IJR/IMR Guidance).

2.1. Related Studies

The following studies were reviewed for their applicability to the proposed modifications to the GWMP at Virginia Route 123 (Chain Bridge Road/Dolley Madison Boulevard) interchange. Relevant data from these studies were used as appropriate to support the development of this IMR:

• George Washington Memorial Parkway North Section Improvements (from Spout Run Parkway to I-495): Candidate Alternatives Report – February 2, 2006 o Key Information: Purpose of North Section Improvements, Route 123 Interchange Alternatives

• George Washington Memorial Parkway North Environmental Assessment Traffic Operation Analysis – April 2017 o Key Information: Baseline volumes, VISSIM model.

2.2. Key Assumptions

Key assumptions used to develop this IMR are as follows:

Study Area: The Study Area for this IMR is summarized in Section 1.3. The Study Area extends along the GWMP from south of the Spout Run Parkway merge/diverge to north of the GWMP/CIA interchange. On Virginia Route 123 (Chain Bridge Road/Dolley Madison Boulevard) the Study Area extends from west of Merchant Lane/Savile Lane to east of Crest Lane/McCay Lane.

Existing Year and Opening Year: An Existing Year of 2017 and an Opening Year of 2025 were assumed for this study. Per VDOT and EFLHD, it was agreed that future year 2040 (the MWCOG regional Long Range Transportation Plan (LRTP) horizon year) would not be included in this IMR. Additionally, it was agreed that while Existing Year volumes would be developed, existing analysis results would not be included as part of this IMR.

Peak Hours for Analysis: The weekday AM and PM peak hours were identified as the critical periods for analysis. These peaks were selected due to higher total traffic volumes and because the GWMP/Route 123 interchange serves as a connection between two primary commuter routes.

Traffic Data: Updated traffic volume data was obtained in April 2017 for the GWMP/Route 123 interchange and intersections along Route 123. Additional information regarding the traffic volume data used for this study can be found in Chapters 3 and 6.

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Crash Data: Crash data for Route 123 was provided by VDOT for the three-year period between January 1, 2014, and December 31, 2016. Crash data for the GWMP was provided by EFLHD for the period between January 1, 2010, and January 1, 2012. The most recent three-year period for each segment was analyzed, and additional information on the crash data and analysis can be found in Chapter 3.

Future Traffic Forecasts: The Opening Year (2025) traffic forecasts for this study were developed by determining future year linear growth from the ADTs of the MWCOG models. These growth rates were applied to the Existing balanced turning movement volumes to develop Opening Year AM/PM peak hour turning movement volumes. A complete summary of the traffic forecasting process used to develop the volumes for this study can be found in Chapter 6.

Future Transportation Network Improvements: This IMR assumes no other future improvements to the transportation network in the Study Area.

Alternatives: Alternative 4 and Alternative 5 from the George Washington Memorial Parkway North Section Improvements Candidate Alternatives Report (February 2, 2006) were analyzed as part of this study. Additional detail on the alternatives can be found in Chapters 4 and 5.

2.3. Traffic Analysis Methodology

The nature of the proposed improvements and the traffic characteristics of the Study Area indicate that several methodologies are appropriate for evaluating operations for this IMR.

Mainline GWMP Operations and Ramps: Based on a review of the specific characteristics of this project and the alternatives likely to be considered, it was concluded that the HCS 7 software, implementing the 6th edition of the Highway Capacity Manual (HCM), would be most appropriate to evaluate operations along GWMP. HCS provides spot analyses of locations along the corridor, including freeway segments, and merge, diverge and weaving segments. Key measures of effectiveness from HCS 7 evaluated for this IMR include density (passenger cars/mile/lane), speed (mph), and level-of-service (LOS). These MOEs were used to compare the No Build and Build Alternatives and to verify that the proposed modifications will provide safe and efficient operations along the GWMP. The results of the HCS 7 analyses are summarized in Chapter 7 of this report.

However, the analyses performed using the HCS 7 software do not account for the potential impacts of upstream or downstream bottlenecks on a freeway segment or junction. Therefore, the microsimulation tool VISSIM (Version 7.00 Build 16) was utilized to develop a simulation model of the entire study area of the GWMP, including all of the defined study area intersections on Route 123. This model was used to evaluate the overall operations of the corridor and the interaction between segments/roadways. Key measures of effectiveness from VISSIM evaluated for this IMR include density (vehicles/mile/lane), speeds (mph), and level-of-service (LOS). All VISSIM results were based on an average of 10 one hour simulation runs. These MOEs were used to compare the No Build and Build Alternatives and validate the results determined from the HCS 7 analysis.

Local Roadway Network: Utilizing the standard methodologies presented in the 2010 Highway Capacity Manual, the software package Synchro Version 9.1 (Build 912, Revision 4) was utilized to assess operations at the study intersections along Route 123 (Chain Bridge Road/Dolley Madison Boulevard).

Measures of effectiveness reported from Synchro (applying the HCM Reports feature) for the signalized

Interchange Modification Report Page 14 and unsignalized intersections along Route 123 include level of service (LOS), volume to capacity (v/c) ratio, and average estimated vehicle delay.

Similar to the analyses performed for the mainline, Synchro software does not account for the potential impacts of upstream or downstream bottlenecks/queues. Therefore, the VISSIM model was utilized to evaluate the overall operations of the Route 123 corridor and any interactions between adjacent signals.

Key measures of effectiveness from VISSIM evaluated for the local roadway network include 95th percentile queue lengths. All VISSIM results were based on an average of 10 one hour simulation runs.

These queue lengths were used to compare the No Build and Build Alternatives and validate the results determined from the Synchro analysis.

Additional information regarding the operations of the local roadway network and ramps can be found in Chapters 3 and 7.

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3. EXISTING CONDITIONS

3.1. Demographics

The GWMP interchange with Route 123 is located in the McLean area of Fairfax County, Virginia. Route 123 runs through the center of Fairfax County in a crescent shape, connecting a number of the most urbanized areas in the County. According to the 2010 census, Fairfax County’s population was approximately 1,081,725, and there were approximately 391,627 housing units located within the County. McLean is a census-designated area that has a population of 48,115 and is home to the headquarters of the United States Central Intelligence Agency (CIA).

3.2. Existing Land Use

The GWMP runs parallel to the western shore of the Potomac River and is bordered by protected park land and several NPS recreational sites. Along Route 123, the land use is primarily residential in nature.

The CIA headquarters is located northwest of the GWMP/Route 123 interchange. A small gas station is located on the southwest quadrant of the Route 123 and Kirby Road intersection.

3.3. Existing Roadway Network

The Study Area for this IMR includes roadways of varying types, ranging from National Highway System (NHS) facilities to local roads, as discussed below:

George Washington Memorial Parkway (GWMP): GWMP is classified as part of the National Highway System (NHS) and is owned and maintained by the NPS. The roadway runs parallel to the western shore of the Potomac River south from the Capital Beltway Interstate 495 at the American Legion Bridge through Fairfax and Arlington Counties and the City of Alexandria to Mount Vernon. The Parkway provides access to several NPS recreational sites and also serves as a major commuter route between Northern Virginia and Washington, DC. The Parkway is a controlled access roadway with a posted speed limit of 50mph. The roadway has two lanes per direction and is comprised of two separate horizontal and vertical alignments for the northbound and southbound directions between the Spout Run Parkway and Capital Beltway interchanges. The GWMP typically has unpaved shoulders and a wide grassy median.

Virginia Route 123 – Chain Bridge Road/Dolley Madison Boulevard (Route 123): Route 123 is a VDOT owned and maintained Other Principal Arterial that runs through the center of Fairfax County in a crescent shape, connecting a number of the most urbanized areas in the County. Route 123 is part of the National Highway System. To the west of the GWMP interchange, Dolley Madison Boulevard is a four-lane divided highway with a posted speed of 45 mph and is characterized as a full access roadway with turn bays and signalized intersection. East of the interchange with the GWMP, Chain Bridge Road transitions to a two-lane full access roadway with a posted speed of 30mph and several residential driveways and neighborhood access points.

Merchant Lane/Savile Lane: Merchant Lane/Savile Lane are local roads with one lane in each direction that provide access for primarily residential land uses to Route 123.

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Kirby Road (VA-695): Kirby Road is a major collector with one lane in each direction that is maintained by VDOT.

Pine Tree Road: Pine Tree Road is a local road with one lane in each direction that provides access for residential land uses to Route 123.

Crest Lane/McCay Lane: Crest Lane/McCay Lane are local roads with one lane in each direction that provide access for primarily residential land uses to Route 123.

3.4. Alternative Travel Modes

There are few options within the Study Area and surrounding area for the use of alternative travel modes.

Rail Service: No passenger rail service is available in or around the Study Area.

Bus Service: The Washington Metropolitan Area Transit Authority (WMATA) provides regular, fixed-route/fixed schedule service through the study area. The Chain Bridge Road Line (Routes 15K & 15L) provides service between the East Falls Church Metro Station and the Rosslyn Metro Station. Both routes travel along Route 123 west of the GWMP/Route 123 interchange. Route 15L travels along Chain Bridge Road east of the interchange and Route 15K uses the GWMP south of the interchange. Both routes provide weekday peak period service with headways of roughly 30 minutes.

High-Occupancy Vehicle (HOV) Alternatives: No High-Occupancy Vehicle (HOV) lanes exist in or around the Study Area.

3.5. Interchanges

There are three interchanges along GWMP located within the Study Area. A description of the configuration for each interchange is provided below:

GWMP at Route 123 Interchange: Route 123 crosses the GWMP at a point approximately halfway between the Capital Beltway and the merge with Spout Run Parkway. The Route 123 interchange serves as a connection between two primary commuter routes. A large portion of the traffic carried by this interchange includes vehicles traveling between Washington, DC, (to the southeast), and McLean or Tysons Corner (to the west). As a result, two of the ramps carry traffic volumes that are five to ten times higher than the other ramps: (1) from northbound GWMP to westbound Route 123 and (2) from eastbound Route 123 to southbound GWMP.

The interchange can be described as a partial cloverleaf with loop ramps and directional ramps in three out of the four quadrants of the interchange: northeast, northwest, and southwest. In the southbound lanes of GWMP a unique traffic pattern exists at the interchange where through traffic is forced to use only the single left-hand lane while the right-hand lane terminates at the ramp to eastbound Route 123.

The right-hand lane on the southbound GWMP picks up again at the merge point of the on-ramp from eastbound Route 123.

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GWMP at CIA Interchange: Located to the north of the GWMP at Route 123 interchange, access to the CIA from the GWMP is provided via a trumpet interchange. The CIA interchange consists of a two-lane overpass and four ramps; two ramps convey southbound GWMP traffic entering or leaving the CIA and two ramps provide service for northbound GWMP traffic. The CIA main entrance gate and adjacent ramp terminals are oriented immediately west of the GWMP. All traffic movements outside of the gate are free-flow.

GWMP at Spout Run Parkway Interchange: Located to the south of the GWMP at Route 123 interchange, Spout Run Parkway diverges/merges with the GWMP. In the northbound direction, three lanes feed two northbound lanes on the GWMP and two westbound lanes on Spout Run Parkway, with the center lane operating as a choice lane. In the southbound direction, two lanes on Spout Run Parkway merge to one lane before merging with the GWMP. A full add lane is provided for this merge onto the southbound GWMP mainline. This three-lane southbound section then transitions into only two southbound lanes between the Spout Run Parkway and the Francis Scott Key Bridge.

3.6. Existing Data

The existing traffic volume used in this study is summarized in Chapter 6. Existing data was compiled from a variety of sources:

• 48-hour classification counts for all GWMP/Route 123 interchange ramps and GWMP mainline were collected in April 2017.

• AM and PM peak period turning movement counts were collected at five intersections along Route 123 (Chain Bridge Road/Dolley Madison Boulevard): Crest Lane, Northbound GWMP Ramps, Pine Tree Road, Kirby Road, and Merchant Lane in April 2017.

• Data from the George Washington Memorial Parkway North Environmental Assessment Traffic Operation Analysis, which was provided by VDOT & FHWA/EFL, was used for the CIA ramps and Spout Run Parkway ramps .

Based on the available data sources, a network of existing 2017 AM and PM peak hour volumes were compiled. See Chapter 6 for additional detail.

3.7. Operational Performance

Operational analysis for this IMR was conducted using the analysis tools HCS7 and Synchro Version 9.1 (Build 912, Revision 4) as well as the microsimulation tool VISSIM (Version 7.00 Build 16). HCS7 and Synchro are based on the methodologies presented in the Highway Capacity Manual. The HCS7 software was used for capacity analyses for freeway segments, weaves, and ramp junctions along GWMP. Synchro was used for capacity analyses for the ramp terminal intersections and adjacent intersections along the Route 123 corridor. Supplemental analyses were conducted using VISSIM.

VISSIM is a microsimulation modeling software that can represent traffic flow on roadway networks containing both surface streets and freeways. VISSIM is capable of assessing the interaction between adjacent freeway segments and/or intersections, particularly under saturated or congested conditions.

VISSIM was used for this study to supplement the HCS7 analyses along the GWMP corridor and to provide maximum queue lengths for the Synchro analyses along the Route 123 corridor.

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3.7.1. Base Model Development and Calibration

The microsimulation traffic analysis in VISSIM was conducted based on the processes described in VDOT’s Traffic Operations and Safety Analysis Manual (TOSAM) – Version 1.0 and the VDOT VISSIM User Guide Version 1.0. A base VISSIM model was developed using existing scaled aerial photography for the project Study Area. The existing AM and PM peak hour volumes were then input in VISSIM, and the model was run using a 30 minute initialization period followed by a one hour recording period. The model runs were recorded to determine how closely the simulation matched the field counted traffic volumes and traffic speeds from INRIX.

INRIX gathers speed positions from real-world vehicles to determine the average speed for all significant roads and gathers and archives real-time traffic data at time periods down to one minute intervals. The University of Maryland and INRIX teamed together as part of the I-95 Coalition Vehicle Probe Project to make this data available across 10 states through the RITIS. The Regional Integrated Transportation Information System (RITIS) is an automated data sharing, dissemination, and archiving system that includes many performance measure, dashboard, and visual analytics tools that help agencies to gain situational awareness, measure performance, and communicate information between agencies and to the public. Speeds from RITIS/INRIX that were collected for the time period between March 1 and March 30, 2017 on Tuesdays through Thursdays during the AM (7-9AM) and PM (4:30-7PM) peak periods.

These observed travel speeds were then input into the VISSIM model used for this IMR analysis.

To confirm the calibration of the model, the simulated traffic volumes, speeds, and travel times along the GWMP and Route 123 were compared to the INRIX and field collected data. Default parameters were changed as needed during calibration to ensure model outputs were within the TOSAM microsimulation model calibration thresholds. The TOSAM calibration thresholds are summarized in Table 3-1.

Table 3-1: TOSAM Microsimulation Model Calibration Thresholds

Source: TOSAM – Version 1.0 (November 2015)

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For all analysis scenarios, the AM and PM peak models were run for a total of ten (10) one-hour simulations (based on unique random number seeds) with a 30 minute initialization period preceding data collection. The number of runs was determined by utilizing the VDOT Sample Size Determination Tool (Version 2.0). The Sample Size Determination Tool measured variations in average segment speed over 6 segments from an initial 10 runs in both the AM and PM peak hour simulations as outlined in TOSAM. The tool determined the 10 runs in both the AM and PM VISSIM models met the required tolerance error and confidence intervals and no additional runs were required.

Table 3-2 and Table 3-3 include a comparison of the field-collected existing AM and PM peak hour traffic volumes to the throughput reported in the existing AM and PM peak VISSIM models. The comparison was performed for each of the mainline GWMP and Route 123 segments upstream and downstream of the interchange as well as each of the interchange ramps. The model volumes are based on an average of ten (10) simulation runs.

Table 3-2: Comparison of Existing Throughput versus Model Throughput – AM Peak Hour

Existing VISSIM Difference (%) Threshold (%) 2070 1958 -5% 5% 2650 2656 0% 5% 140 150 7% 15% 350 344 -2% 10% 15 13 -13% 20% 940 933 -1% 10% 265 281 6% 15%

1015 1028 1% 5% 2695 2693 0% 5% 3240 3245 0% 5% 1915 1924 0% 5% 1410 1430 1% 5% 1030 1029 0% 5% 530 538 2% 10%

VA 123 WB downstream of Kirby VA 123 EB upstream of Kirby VA 123 WB upstream of Crest Ln VA 123 EB downstream of Crest Ln

GW Pkwy SB On-Ramp from VA 123 WB GW Pkwy NB Off-Ramp to VA 123 EB/WB GW Pkwy SB Off-Ramp to VA 123 EB GW Pkwy SB On-Ramp from VA 123 EB GW Pkwy SB downstream of VA 123 GW Pkwy NB upstream of VA 123

AM Peak - Throughput Data Collection Measurement

GW Pkwy SB upstream of VA 123 GW Pkwy NB downstream of VA 123 GW Pkwy SB Off-Ramp to VA 123 WB GW Pkwy NB On-Ramp from VA 123 EB/WB

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Table 3-3: Comparison of Existing Throughput versus Model Throughput – PM Peak Hour

Existing VISSIM Difference (%) Threshold (%) 2275 2279 0% 5% 1850 1837 -1% 5% 125 125 0% 15% 285 275 -4% 10% 110 106 -4% 20% 1365 1364 0% 5% 170 171 1% 15% 1500 1456 -3% 5% 3590 3534 -2% 5% 2930 2921 0% 5% 1780 1774 0% 5% 2675 2589 -3% 5% 850 848 0% 10% 1170 1136 -3% 5%

VA 123 WB upstream of Crest Ln

PM Peak - Throughput

VA 123 EB downstream of Crest Ln

Data Collection Measurement

GW Pkwy SB On-Ramp from VA 123 EB GW Pkwy SB downstream of VA 123 GW Pkwy NB upstream of VA 123 VA 123 WB downstream of Kirby VA 123 EB upstream of Kirby

GW Pkwy SB Off-Ramp to VA 123 WB GW Pkwy NB On-Ramp from VA 123 EB/WB GW Pkwy SB On-Ramp from VA 123 WB GW Pkwy NB Off-Ramp to VA 123 EB/WB GW Pkwy SB Off-Ramp to VA 123 EB

GW Pkwy SB upstream of VA 123 GW Pkwy NB downstream of VA 123

The results in Table 3-1 and Table 3-2 indicate that the simulated GWMP and Route 123 link volumes and interchange ramps within VISSIM closely match the field observed AM and PM peak traffic volumes.

Furthermore, all of the percent differences between the existing counts and VISSIM modeled volumes fall within the respective thresholds outlined in TOSAM.

A comparison of the average VISSIM-modeled vehicle speeds indicated that the model was accurately modeling the travel speeds along GWMP in both directions during both peak hours. The simulated speeds over 6 segments were compared to the existing average speeds from INRIX on GWMP and Route

123. Table 3-4 and Table 3-5 include a comparison of the existing AM and PM peak average segment speeds to the average segment speeds reported in the existing AM and PM peak VISSIM models.

Table 3-4: Comparison of Existing Average Speeds versus Model Average Speeds – AM Peak Hour

Number Segment INRIX VISSIM Difference Threshold 1 GW Pkwy SB (From I-495 to VA 123) 47 44 -3 7 2 GW Pkwy SB (From VA 123 to Spout Run) 26 32 6 7 3 GW Pkwy NB (From Spout Run to VA 123) 50 53 3 7 4 GW Pkwy NB (From VA 123 to I-495) 55 53 -2 7 5 VA 123 EB (From Georgetown Pike to GWMP) 34 34 0 5 6 VA 123 WB (From Kirby Rd to Georgetown Pike) 37 32 -5 5

AM Peak - Speeds (mph)

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Table 3-5: Comparison of Existing Average Speeds versus Model Average Speeds – PM Peak Hour

Number Segment INRIX VISSIM Difference Threshold 1 GW Pkwy SB (From I-495 to VA 123) 45 51 6 7 2 GW Pkwy SB (From VA 123 to Spout Run) 43 50 7 7 3 GW Pkwy NB (From Spout Run to VA 123) 42 49 7 7 4 GW Pkwy NB (From VA 123 to I-495) 27 30 3 7 5 VA 123 EB (From Georgetown Pike to GWMP) 17 18 1 5 6 VA 123 WB (From Kirby Rd to Georgetown Pike) 37 32 -5 5

PM Peak - Speeds (mph)

The results in Table 3-4 and Table 3-5 indicate that the simulated AM and PM peak hour speeds are within the TOSAM required 7 mph, for freeway links on GWMP, and 5 mph, for arterial links on Route 123, of the average AM and PM peak hour INRIX speeds for each segment and time period.

Comparisons of the AM and PM VISSIM-modeled travel times versus the INRIX reported existing AM and PM travel times is provided in Table 3-6 and Table…