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ARMY NAVY DRIVE
MARCH | 2017TRAFFIC STUDY
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Traffic Study
Army Navy Drive Traffic Study
Arlington County, VA
Prepared For: Arlington County, Division of Transportation 2100 Clarendon Boulevard, Suite 900 Arlington, VA 22201 (703) 228-3681
Prepared By: Kittelson & Associates, Inc. 1850 Centennial Drive, Suite 130 Reston, Virginia 20191 (703) 885-8970
Project Manager: Brandon Nevers, Pr. Eng., P.E. Lead Analyst: Jon Crisafi, P.E.
Project No. 11834.32
March 2017 Updated: June 2017
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TABLE OF CONTENTS
Executive Summary ................................................................................................................................ 1
Operations Findings ..................................................................................................................................................................... 1
Scenario Findings ......................................................................................................................................................................... 4
Geometric Recommendations ..................................................................................................................................................... 5
Signal-Related Recommendations ............................................................................................................................................. 12
Introduction ..................................................................................................................................... 15
Study Area ................................................................................................................................................................................. 15
Scope of Project......................................................................................................................................................................... 15
Existing Conditions ............................................................................................................................... 21
Transportation Facilities ............................................................................................................................................................ 21
Transit Facilities ......................................................................................................................................................................... 22
Existing Conditions Traffic Analysis ........................................................................................................................................... 22
Existing Conditions Findings ...................................................................................................................................................... 26
Travel Demand Modeling ..................................................................................................................... 29
Network Modifications – 2015 Model ....................................................................................................................................... 29
Study Area Conditions – 2020 Model ........................................................................................................................................ 32
Study Area Conditions – 2040 Model ........................................................................................................................................ 32
Design Concept Refinement ................................................................................................................ 35
Initial Design Concept ................................................................................................................................................................ 35
Initial Observations.................................................................................................................................................................... 35
Bicycle Treatments .................................................................................................................................................................... 37
Transit Treatments .................................................................................................................................................................... 37
Qualitative Evaluation ............................................................................................................................................................... 45
Concept Refinement .................................................................................................................................................................. 46
Future Conditions Analysis................................................................................................................... 49
Background Developments ....................................................................................................................................................... 49
Year 2020 and 2040 No-Build .................................................................................................................................................... 50
Year 2020 and 2040 Build .......................................................................................................................................................... 59
Comparison Across All Scenarios ............................................................................................................................................... 68
Summary of Findings ............................................................................................................................ 81
Scenario Findings ....................................................................................................................................................................... 84
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Recommendations ............................................................................................................................... 87
Geometric Recommendations ................................................................................................................................................... 87
Signal-Related Recommendations ............................................................................................................................................. 93
References ..................................................................................................................................... 96
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LIST OF FIGURES
Figure 1 – S Joyce Street/Army Navy Drive Recommendations Summary ............................................ 6
Figure 2 – Pentagon Mall Garage/Army Navy Drive Recommendations Summary .............................. 7
Figure 3 – S Hayes Street/Army Navy Drive Recommendations Summary ........................................... 8
Figure 4 – S Fern Street/Army Navy Drive Recommendations Summary ............................................. 9
Figure 5 – S Eads Street/Army Navy Drive Recommendations Summary ........................................... 10
Figure 6 – Army Navy Drive/12th Street S Recommendations Summary ........................................... 11
Figure 7 – Existing Lane Configurations and Traffic Control Devices ................................................... 16
Figure 8 – Existing Traffic Operations – Weekday AM Peak Hour ....................................................... 24
Figure 9 – Existing Traffic Operations – Weekday PM Peak Hour ....................................................... 25
Figure 10 – Modified Network in Army Navy Drive Study Area .......................................................... 30
Figure 11 – Original Network in Army Navy Drive Study Area ............................................................ 31
Figure 12 – Initial Design Concept Considerations .............................................................................. 36
Figure 13 – S Joyce Street Median Transit-Lanes Concept Movements .............................................. 39
Figure 14 – Parking Garage Driveway Median-Transit-Lanes Concept Movements ........................... 40
Figure 15 – S Hayes Street Median-Transit-Lanes Concept Movements ............................................ 40
Figure 16 – S Joyce Street Outside-Transit-Lanes Concept Movements ............................................. 42
Figure 17 – Parking Garage Driveway Outside-Transit-Lanes Concept Movements ........................... 43
Figure 18 – S Hayes Street Outside-Transit-Lanes Concept Movements ............................................ 43
Figure 19 – Joyce Street AM (left) and PM (right) Ring-and-Barrier .................................................... 44
Figure 20 – Joyce Street AM (left) and PM (right) Ring-and-Barrier .................................................... 44
Figure 21 – Hayes Street AM (left) and PM (right) Ring-and-Barrier ................................................... 45
Figure 22 – Location of Background Developments ............................................................................ 49
Figure 23 – No-Build Lane Configuration and Traffic Control Devices ................................................ 51
Figure 24 – Year 2020 No-Build Traffic Operations – Weekday AM Peak Hour .................................. 52
Figure 25 – Year 2020 No-Build Traffic Operations – Weekday PM Peak Hour .................................. 53
Figure 26 – Year 2040 No-Build Traffic Operations – Weekday AM Peak Hour .................................. 54
Figure 27 – Year 2040 No-Build Traffic Operations – Weekday PM Peak Hour .................................. 55
Figure 28 – Build Lane Configuration and Traffic Control Devices ...................................................... 63
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Figure 29 – Year 2020 Build Traffic Operations – Weekday AM Peak Hour ........................................ 64
Figure 30 – Year 2020 Build Traffic Operations – Weekday PM Peak Hour ........................................ 65
Figure 31 – Year 2040 Build Traffic Operations – Weekday AM Peak Hour ........................................ 66
Figure 32 – Year 2040 Build Traffic Operations – Weekday PM Peak Hour ........................................ 67
Figure 33 – Average Network Delay for All Vehicles by Scenario ........................................................ 69
Figure 34 – Average Network Delay for Passenger Cars by Scenario .................................................. 69
Figure 35 – Average Network Delay for Transit by Scenario ............................................................... 70
Figure 39 - Summary of Transit Travel Time Increases at S Hayes St/Army Navy Dr .......................... 71
Figure 40 – Spot Speeds during AM Peak Hour ................................................................................... 73
Figure 41 – Spot Speeds during PM Peak Hour ................................................................................... 73
Figure 42 – Intersection Delay during AM Peak Hour ......................................................................... 75
Figure 43 – Intersection Delay during PM Peak Hour .......................................................................... 75
Figure 44 – Measured Southbound Queue Storage at S Hayes Street/Army Navy Drive ................... 76
Figure 45 – S Joyce Street/Army Navy Drive Recommendations Summary ........................................ 87
Figure 46 – Pentagon Mall Garage/Army Navy Drive Recommendations Summary .......................... 88
Figure 47 – S Hayes Street/Army Navy Drive Recommendations Summary ....................................... 89
Figure 48 – S Fern Street/Army Navy Drive Recommendations Summary ......................................... 90
Figure 49 – S Eads Street/Army Navy Drive Recommendations Summary ......................................... 91
Figure 50 – Army Navy Drive/12th Street S Recommendations Summary ......................................... 92
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LIST OF TABLES
Table 1 Intersections with Peak Hour LOS E or Worse by Scenario....................................................... 2
Table 2 Army Navy Drive Traffic Study Intersections .......................................................................... 15
Table 3 Summary of Roadways within Study Area .............................................................................. 21
Table 4 Existing Peak Hour Conditions - Intersection Delay and LOS .................................................. 23
Table 5 Two-way Volume Comparison for Army Navy Drive ............................................................... 31
Table 6 Lane-Configuration Revisions for Median-Transit-Lanes Concept .......................................... 38
Table 7 Estimated Cycle-Length Increase or Decrease (in Seconds Compared to Existing Conditions)
Required to Accommodate Demand with Median Transit Lanes ........................................................ 39
Table 8 Lane-Configuration Revisions for Median-Transit-Lanes Concept .......................................... 41
Table 9 Estimated Cycle-Length Increase or Decrease (in Seconds Compared to Existing Conditions)
Required to Accommodate Demand with Outside Transit Lanes ....................................................... 42
Table 10 Evaluation of Median and Outside Transit Lanes ................................................................. 46
Table 11 Transit Travel Times .............................................................................................................. 71
Table 12 Intersection Performances during AM Peak Hour ................................................................ 74
Table 13 Intersection Performances during PM Peak Hour ................................................................ 74
Table 14 Maximum simulated Queues at Southbound Hayes Street/Army Navy Drive Intersection 76
Table 15 Maximum simulated Queues at Eastbound Eads Street/Army Navy Drive Intersection ..... 77
Table 16 Intersections with Peak Hour LOS E or Worse by Scenario .................................................. 82
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APPENDICES
Appendix A - Calibration Summary Memorandum
Appendix B – VISSIM Existing Traffic Operations Results
Appendix C – TDM Network Modifications
Appendix D – TDM Model Volume Plots
Appendix E – Existing and Future TDM Volumes and Field Measurements
Appendix F – Transit Lane Concept Analysis
Appendix G – Background Development Site Plans
Appendix H – VISSIM Future Traffic Operations Results
Appendix I – Signal Timing Parameters
SECTION 1
Executive Summary
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EXECUTIVE SUMMARY
Arlington County has begun an effort to modify the existing Army Navy Drive corridor in Pentagon City
to better accommodate transit users, pedestrians, and cyclists. In support of this effort, a detailed
traffic operations analysis was performed for the Design Concept developed by the County, which
includes a two-way protected bike lane, median transit way, and enhanced pedestrian crossings. This
concept was evaluated through microsimulation modeling. Existing conditions models were developed
and calibrated for weekday a.m. and p.m. peak periods. These models were then used to develop
future scenarios for Year 2020 (opening year) and Year 2040 (design year) for both the no-build
condition (background development only) and the build condition (background development and
implementation of the Design Concept).
The Design Concept evolved through a series of multimodal operational analyses and discussions with
Arlington County staff. This resulted in modifications to lane configurations at certain intersection
approaches, additional and reconfigured bicycle facilities, and relocated transit lanes from the median
to curbside.
This report summarizes the iterative design and analysis process used to evaluate and modify the
Design Concept along with the overall findings and recommendations for advancing the project forward
to the next stage of the design process.
The following sections highlight the key findings from the operational analyses conducted for existing,
future no-build, and future build conditions.
OPERATIONS FINDINGS
While the purpose of the Design Concept is to promote and accommodate active transportation
(pedestrians and bicyclists) and transit use along Army Navy Drive, this study focuses on the automobile
and transit performance associated with the proposed improvements. Given the right-of-way
constraints along the Army Navy Drive corridor, trade-offs are inherent when accommodating multi-
modal needs. For corridors that undergo complete street improvements to provide pedestrian, bicycle,
and transit facilities, oftentimes traffic operations for vehicles degrade due to the reduction of travel
lanes and intersection capacity. The purpose of this study is to identify the level of impact to traffic
operations along the corridor and identify mitigation strategies to reduce impacts while
accommodating safety and the performance needs of non-auto users.
The operational analysis of existing, future no-build, and build traffic conditions identified several
intersections and movements that experience long queues, traffic congestion, and turning movements
that operate at Level of Service (LOS) E or F, which causes motorists at those movements to experience
high delays. Table 1 summarizes which intersections are anticipated to experience this by scenario.
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Table 1 Intersections with Peak Hour LOS E or Worse by Scenario
Peak Hour Intersection 2015 Existing 2020 No-Build 2020 Build 2040 No-Build 2040 Build
AM
Army Navy Drive & Joyce
Army Navy & Pentagon Mall E E
Army Navy & Hayes E E F
Army Navy & Fern
Army Navy & Eads E E E
Army Navy & 12th* F* F E E F
PM
Army Navy Drive & Joyce
Army Navy & Pentagon Mall
Army Navy & Hayes E
Army Navy & Fern E E
Army Navy & Eads F F F F
Army Navy & 12th* * F F F F
*Indicates unsignalized intersection configuration
While individual intersection operations do not reflect the complete picture of how the system
performs under different Design Concepts, it helps identify the location of bottlenecks and “hot spots”
to warrant more-detailed investigation.
S Joyce Street/Army Navy Drive
Positioned on the western end of the corridor, the intersection at S Joyce Street/Army Navy Drive is
anticipated to operate at LOS D or better under all scenarios. Notable findings include:
The eastbound approach experiences higher delays under the build scenarios notably due to
heavy left-turn movements limited by protected-only phasing.
The 2040 build scenario is exacerbated by heavier volume demands on all approaches,
particularly left-turns.
Pentagon Mall Garage/Army Navy Drive
The intersection at Pentagon Mall Garage/Army Navy drive is expected to experience LOS E or worse
under both 2040 no-build and build scenarios during the weekday a.m. peak hour. Notable findings
include:
The westbound left-turn movement into the parking garage experiences the highest delay of all
movements at the intersection in all scenarios.
Reconfiguration of the parking garage exit in the build scenario is anticipated to accommodate
traffic demands without undue delay and queuing.
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S Hayes Street/Army Navy Drive
The intersection of S Hayes Street/Army Navy Drive is among the most critical along the corridor. It is
projected to operate at LOS E, or worse, under both build scenarios and 2040 no-build conditions
during the weekday a.m. peak hour. In all scenarios, the intersection’s connection to Interstate-395 (I-
395) and Washington Boulevard required queuing to be managed on the southbound approach to
prevent spillback onto the freeways. Notable findings include:
Northbound left turns experience high delays under both build and no-build conditions.
Southbound lefts experience high delays attributed to high demand.
Dual southbound left turn lanes were analyzed but have limited benefit due to queuing on the
downstream approach.
Results from the Vissim simulation analysis indicate that the maximum queue on the
southbound approach is not anticipated to spillback onto either I-395 or Washington Boulevard
under any future scenario analyzed.
S Fern Street/Army Navy Drive
The S Fern Street/Army Navy Drive intersection is mostly a point between the bottlenecks at S Hayes
Street and S Eads Street. The intersection is anticipated to operate at LOS E, or worse, only during the
2040 scenarios, mostly driven by queue spillback and heavy side street demands. Notable findings
include:
The northbound approach is anticipated to experience high delays in all future scenarios.
Eastbound delays at the intersection are mostly due to queue spillback from the S Eads
Street/Army Navy Drive intersection.
S Eads Street/Army Navy Drive
The intersection at S Eads Street/Army Navy Drive is a bottleneck along the corridor, given it is used to
access northbound I-395 and bus routes destined to the Pentagon. Both no-build and build lane
configurations have notable limitations in facilitating the traffic demand in future scenarios. Notable
findings include:
Eastbound left-turn queues consistently spill back through S Fern Street and S Hayes Street,
limiting throughput of the western intersections.
The heavy eastbound left-turn movement demand conflicts with a heavy westbound through
movement demand, thus competing for green time and causing delays to automobiles and
buses.
Northbound S Eads Street is constrained by a single approach lane given the relatively short
turn pockets.
The I-395 HOT lanes and associated improvements are expected to improve the operations at S
Eads Street and may relieve some of the anticipated congestion.
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Army Navy Drive/12th Street S
The intersection is currently unsignalized. Based on Arlington County plans, the intersection is planned
to be signalized in conjunction with the neighboring Clark Street/12th Street S intersection in the future.
The signalization will include the addition of median-running transit lanes as part of the 12th Street S
transit facility project. These improvements were assumed in the all future build and no-build
conditions. Notable findings from the analysis of this intersection include:
If unsignalized, the southbound movements are projected to experience significant queuing and
delay.
If signalized based on current plans, the following operational inefficiencies are anticipated: o Long clearance intervals due to the separation of the two intersections (12th Street and
Clark Street); o Limited flexibility to reallocate green time across phases due to the two-intersection
phasing. o The intersection (in conjunction with 12th Street S/Clark Street) has heavy turning
volumes compared to through volumes.
SCENARIO FINDINGS
Existing Conditions
General findings from the simulation analysis of existing conditions include:
Simulation results match with field observations of queues and driver behavior.
Simulation results at the intersection level are comparable to the Synchro analysis results.
Future No-Build Conditions Findings
General findings from the simulation analysis of no-build conditions include:
Significant congestion was observed in both future years during the weekday a.m. and p.m.
peak hours, notably at S Hayes Street, S Fern Street, S Eads Street and 12th Street
intersections.
Queue storage on the southbound S Hayes Street approach (I-395 ramp) is accommodated
through 2040 for both a.m. and p.m. peak hours.
The observed bottleneck is the eastbound approach at S Eads Street/Army Navy Drive. The
current eastbound lane configuration consists of a left-through and through-right layout,
which negatively impacts the progression of left-turn and through movements. The future-
year simulation analysis shows that demand is heavy on all legs with the predominant
conflicting movements being the eastbound left-turn movement and westbound through
movement. With heavy volumes destined to northbound I-395 and the limitation of a single
receiving lane, congestion is not expected to be alleviated by signal timing and phasing
improvements.
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Future Build Conditions Findings
General findings from the simulation analysis of build conditions include:
Significant congestion was observed in both future years during both weekday a.m. and
p.m. peak hours, notably at S Hayes Street, S Fern Street, S Eads Street, and 12th Street S
intersections.
Queue storage on the southbound S Hayes Street approach (I-395 ramp) accommodates the
back of queue through 2040 for both weekday a.m. and p.m. peak hours.
Both build and no-build conditions show a major network bottleneck at the S Eads
Street/Army Navy Drive intersection.
o Similar to the no-build analysis the future-year simulation analysis indicates heavy
demand on all legs; the main conflicting movements are the eastbound left-turn
movement and westbound through movement. With heavy volumes destined to the
northbound direction towards I-395 and the limitation of a single receiving lane,
congestion is not expected to be alleviated by signal timing and phasing improvements.
o Queue storage for the eastbound left-turn is recommended to be extended as far as
possible, but block spacing remains a limiting factor. Even with maximum storage, left-
turn queue spillback is anticipated.
The overall Design Concept reduces vehicular capacity along Army Navy Drive by
reallocating right-of-way to non-auto users. However, as summarized in Table 1, all study
intersections anticipated to operate at LOS E, or worse, in 2040 will do so under both build
and no-build conditions, with the only exception being the intersection of Army Navy
Drive/S Hayes Street.
GEOMETRIC RECOMMENDATIONS
The following section summarizes the geometric recommendations, shown graphically in Figures 1
through 6.
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1. Joyce Street/Army Navy Drive
a. Northbound approach should be designed with a bike box configuration to
accommodate WB cyclists exiting the bicycle facility and continuing WB on Army Navy
Drive or turning right onto Joyce Street.
b. Westbound approach should be able to accommodate U-turns to provide access to the
Harris Teeter parking garage due to closing the existing median left-turn lane.
c. Southbound approach requires maintaining a left-turn lane with minimum storage
consistent with existing configuration.
Figure 1 – S Joyce Street/Army Navy Drive Recommendations Summary
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2. Parking Garage/Army Navy Drive
a. The northbound approach should be modified to a dedicated left-turn, dedicated
through, and dedicated right-turn lane configuration.
b. Pentagon Transit Center Considerations - Resolution with the ultimate design of the
Transit Center by the Pentagon must consider the west crosswalk as the latest designs
currently do not depict this pedestrian crossing. Include revised southbound approach
to shared left/through lane and dedicated right-turn lane.
c. The westbound left-turn lane requires additional storage.
i. The current left-turn lane length shown in the Design Concept between Parking
Garage (on westbound Army Navy Drive) and Hayes Street (on eastbound Army
Navy Drive) should accommodate anticipated queues.
ii. Storage length of the westbound left-turn lane is as follows:
1. WB Army Navy Drive @ Parking Garage = 130-ft; 75-ft taper
Figure 2 – Pentagon Mall Garage/Army Navy Drive Recommendations Summary
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3. Hayes Street/Army Navy Drive
a. The near-side bus stop along eastbound Army Navy Drive requires pedestrian
accommodations across the two-way bike lanes; consider similar treatment to mid-
block stop between Joyce Street and Parking Garage.
b. The northbound bike lane should be aligned along the curb rather than between the
through and right-turn lanes to prevent right-turning cyclists from conflicting with right-
turning vehicles. The model assumed that northbound left-turning cyclists would merge
into the vehicle lanes, but there are alternatives for accommodating left-turning cyclists.
A two-stage left-turn bike box could be installed or a bike signal/phase could be
considered. Although, an exclusive bike phase would result in a longer cycle length.
c. The southbound right-turn lane should have advanced signage of pedestrian crossing for
the channelized lane to encourage motorists to reduce speeds.
d. Dual southbound left-turn lanes have been considered but are not recommended. The
eastbound downstream through capacity limits any benefit of dual left-turn lanes.
e. Storage length of the left-turns lane are as follows:
i. EB Army Navy Drive @ Hayes Street = 220-ft; 60-ft taper
ii. WB Army Navy Drive @ Hayes Street = 125-ft; 60-ft taper
Figure 3 – S Hayes Street/Army Navy Drive Recommendations Summary
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4. Fern Street/Army Navy Drive
a. Consider access management alternatives, such as limiting ingress at the driveway on
the far-side of eastbound Army Navy Drive at Fern Street and potential to implement
right-out only configuration to reduce conflicts with pedestrians and cyclists.
b. The northbound approach should be reconfigured as a designated left-turn lane,
through lane, and designated right-turn lane.
c. Storage length of the left-turns lane are as follows:
i. EB Army Navy Drive @ Fern Street = 150-ft; 60-ft taper
ii. WB Army Navy Drive @ Fern Street = 50-ft; 60-ft taper
Figure 4 – S Fern Street/Army Navy Drive Recommendations Summary
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5. Eads Street/Army Navy Drive
a. The eastbound left-turn lane requires the maximum storage possible within the block
due to heavy bus movements and traffic demands.
b. Consider revisions to the westbound approach to reduce conflict points; the design
should consider:
i. Restricting westbound traffic movements from US 110 (Jefferson Davis Highway)
from turning left onto Eads Street.
ii. Providing better accommodations at the existing pedestrian crossing on the US-
110 off-ramp. The County will conduct a marked crosswalk study in order to
determine what treatments are warranted for this location. The study will be
submitted to VDOT in a separate memorandum.
c. The northbound approach would benefit from elongating the two-lane cross-section
south to 11th Street S for additional capacity.
d. Storage length of the left-turns lane are as follows:
i. EB Army Navy Drive @ Eads Street = 420-ft; 60-ft taper
ii. WB Army Navy Drive @ Eads Street = 135-ft; 60-ft taper
Figure 5 – S Eads Street/Army Navy Drive Recommendations Summary
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6. Army Navy Drive /12th Street S
a. Transit-only lanes between Army Navy Drive and 12th Street S should be converted to
general traffic lanes to improve traffic throughput.
i. Transit-only lanes between both intersections do not reduce bus delay with
recommended signal timing/phasing, which allows buses to use the segment
exclusively.
b. Prohibit westbound left turns due to sight distance concerns. Must provide westbound
U-turn movement at S Eads Street/12th Street S intersection to access garage.
Figure 6 – Army Navy Drive/12th Street S Recommendations Summary
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SIGNAL-RELATED RECOMMENDATIONS
A 130-second cycle length is recommended for 2020 weekday a.m. peak hour build scenario.
A 140-second cycle length is recommended for 2020 weekday a.m. peak hour and both 2040
weekday a.m. and p.m. peak hour scenarios.
Implement protected-only left-turn phasing along Army Navy Drive to reduce conflicts between
westbound left-turning vehicles, pedestrians, and bicyclists.
Eastbound/westbound bicycle movements along the bike facility will run concurrently with the
eastbound through phase.
Ensure all pedestrian intervals meet MUTCD recommended standards.
The Army Navy Drive/12th Street S intersection meets traffic signal warrants under Year 2020
and Year 2040 volume conditions and should be signalized. It is recommended that this
intersection run on the same controller as Clark Street/12th Street S and will be constructed as
part of the Crystal City Potomac Yard (CCPY) Transitway Extension project.
All analyzed signal timing parameters found in Appendix I.
SECTION 2
Introduction
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INTRODUCTION
The purpose of the Army Navy Drive Traffic Study is to evaluate and provide recommendations for
Arlington County’s proposed Design Concept for Army Navy Drive between Joyce Street and 12th Street,
which is intended to better accommodate transit users, pedestrians, and cyclists. This study analyzes
the operational effects of the reconfigured corridor to identify fatal flaws and areas of potential
improvement as the project progresses toward final design.
STUDY AREA
The study area comprises the northern section of Pentagon City, which is a commercial area due south
of The Pentagon. The area is roughly bounded to the north and west by I-395, to the east by US 1, and
to the south by 15th Street South. Army Navy Drive is the northern most commercial arterial that has
direct access to I-395 and indirect access to US 1. Table 2 details the intersections that are included in
the study analysis.
Table 2 Army Navy Drive Traffic Study Intersections
No. Intersection Control
1 S Joyce St/Army Navy Drive Signalized
2 Mall Driveway/Army Navy Drive Signalized
3 S Hayes St/Army Navy Drive Signalized
4 S Fern St/Army Navy Drive Signalized
5 S Eads St/Army Navy Drive Signalized
6 Army Navy Drive/12th St S Unsignalized
7 S Joyce St @ Bonefish Driveway Signalized
8 S Hayes St/12th St S Signalized
9 S Fern St/12th St S Signalized
10 S Eads St/12th St S Signalized
Figure 7 shows a map of the study area and details the existing lane configurations of the study
intersections.
SCOPE OF PROJECT
The evaluation of the study area has been broken down into the following components:
Evaluation of existing conditions
Travel demand modeling for future traffic volumes
Design Concept evaluation
Evaluation of future conditions
These components are further detailed in subsequent sections of the report.
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Analysis Periods
Traffic data were examined to identify which peak hours to analyze in order to provide the most insight
to operational constraints of the roadway network. After reviewing weekend and weekday traffic data,
it was determined that the weekday a.m. and p.m. peak periods were the heaviest traveled.
Future analysis years were determined to remain consistent with the regional travel demand model:
Year 2015 – Existing conditions
Year 2020 – Opening year conditions
Year 2040 – Design year conditions
As a result of these analysis periods, a total of ten (10) scenarios were modeled for the traffic study in
five groupings:
1. 2015 Existing Conditions (AM and PM)
2. 2020 No-build Conditions (AM and PM)
3. 2040 No-build Conditions (AM and PM)
4. 2020 Build Conditions (AM and PM)
5. 2040 Build Conditions (AM and PM)
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SECTION 3
Existing Conditions
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EXISTING CONDITIONS
The Army Navy Drive corridor is a commercial roadway in Arlington County, Virginia, just south of The
Pentagon’s campus. The area is bounded to the north and west by I-395, to the east by US 1, and to the
south by 15th Street South.
TRANSPORTATION FACILITIES
The study area roadway network is comprised of major collectors and minor arterials. The summary of
these facilities is found in Table 3.
Table 3 Summary of Roadways within Study Area
Roadway Functional
Classification1 Orientation Number of Lanes
Posted Speed (mph)2 Sidewalks
Bicycle Lanes
On-Street Parking
Army Navy Drive Major Collector East-West 6 35 Yes No Yes4
Joyce Street Minor Arterial North-South 4 25/353 Yes Yes Yes
Hayes Street Minor Arterial North-South 6 30 Yes Yes Yes
Fern Street Major Collector North-South 2 30 Yes No Yes
Eads Street Major Collector North-South 2 30 Yes Yes Yes
12th Street Major Collector East-West 2 30 Yes No Yes
1 Per VDOT Functional Classification map: http://www.virginiadot.org/projects/fxn_class/maps.asp (Reference 1)
2 Mph represents miles per hour
3 Joyce Street has a posted speed limit of 25 miles per hour south of Army Navy Drive and 35 miles per hour north of Army Navy Drive
4 On-street parking is available on Army Navy Drive west of Fern Street on the south side
As shown in Table 3, the street network in the study area is largely accommodating to urban traffic,
including a mostly comprehensive sidewalk network on all streets and available on-street parking.
The parcels to the north of Army Navy Drive and south of I-395 are mostly surface parking lots, largely
utilized by Pentagon employees. The parcels south of Army Navy Drive are mostly commercial uses
including Pentagon City Mall.
Pedestrian and Bicycle Facilities
Nearly all roadways within the network have pedestrian facilities including sidewalks and crosswalks at
intersections.
Currently Army Navy Drive has no dedicated bicycle facilities; however, three of the major north-south
streets have striped bicycle lanes. Joyce Street and Hayes Street have bicycle lanes on either side of the
street that terminate at Army Navy Drive. Eads Street has a two-way bike lane facility on the west side
of the street. These north-south connections currently end at a major east-west route in Army Navy
Drive leaving cyclists “stranded” without dedicated facilities to proceed. This circumstance provides
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further justification for implementing an east-west facility on Army Navy Drive that would link the trail
connection near Long Bridge Park to the Columbia Pike/S Joyce Street intersection.
TRANSIT FACILITIES
Army Navy Drive currently has six bus stops along the corridor; four westbound stops, and two
eastbound stops. These are simple curb-side signed stops, some providing bus shelters for passengers.
Along Hayes Street is a dedicated bus pull-out stops between Army Navy Drive and 15th Street which
services the Pentagon City Mall and surrounding commercial uses and serves as a connection point to
the Pentagon City METRO station at Hayes Street and 12th Street. Bus routes and stops also run along
Joyce Street and Eads Street.
EXISTING CONDITIONS TRAFFIC ANALYSIS
The traffic study began with developing existing conditions models to provide a datum comparison to
future scenarios. The development of these existing conditions models (for Year 2015 weekday a.m.
and p.m. peak-hour periods) first required a calibration effort to assess how closely the model
replicates real-world conditions. Following the calibration effort, operational performance metrics were
collected and summarized.
Existing Conditions Calibration
Developing existing conditions models requires honing in on key operations and effects that best
replicate real-world conditions in an effort to provide a simulated scenario that is comparable to actual
traffic experiences. The calibration effort was conducted to focus on the following elements per
guidance from the VDOT TOSAM (Reference 2):
Capacity (traffic volumes) – compares the traffic volumes processed at intersections within the
model to turning movement counts collected in the field.
Travel Times – compares simulated vehicle travel times to those collected in the field along
specified routes.
Spot Speeds – compares average vehicle speeds at point locations between simulated vehicles
and vehicle speed data collected in the field.
Visual Calibration – compares qualitative traffic patterns, observed in the field, that have
notable influence on the traffic operations in the study area (e.g. queuing, yielding behavior).
Achieving specified targets across these elements have been agreed to be sufficient to consider the
existing conditions models as acceptable representations of real-world traffic conditions. The details of
the calibration process and target achievement are found in the Calibration Summary Memorandum in
Appendix A.
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Existing Peak Hour Traffic Operations
Existing conditions models were run 10 times each using random vehicle seeding to produce varying
vehicle arrivals in the model. Operational performance metrics were captured for average vehicle delay,
the corresponding Level of Service (LOS), and maximum simulated queue lengths. Figure 8 and Figure 9
summarize the existing conditions intersection operational results during the weekday a.m. and p.m.
peak hours.
Table 4 summarizes the intersection delay and LOS results for the study intersections during the
weekday a.m. and p.m. peak periods under existing traffic conditions. These results were compared
against intersection delay and LOS results presented in the Synchro 9 models prepared by the County.
Table 4 Existing Peak Hour Conditions - Intersection Delay and LOS
Intersection
AM PM
VISSIM Synchro (HCM 2000) VISSIM Synchro (HCM 2000)
Delay LOS Delay LOS Delay LOS Delay LOS
Army Navy Drive & Joyce 21.2 C 19.8 B 26.0 C 26.0 C
Army Navy & Pentagon Mall 24.0 C 14.6 B 17.2 B 14.6 B
Army Navy & Hayes 33.2 C 48.5 D 24.5 C 43.1 D
Army Navy & Fern 18.8 B 13.9 B 22.7 C 21.4 C
Army Navy & Eads 32.9 C 23.7 C 41.3 D 19.5 B
Army Navy & 12th1 51.9 F 239.5 F 11.2 B 25.4 D
Joyce & North Driveway 19.6 C 13.2 B 16.1 C 18.5 C
12th & Hayes 30.6 C 10.3 B 12.8 B 21.6 C
12th & Fern 15.4 B 17.1 B 17.4 B 19.6 B
12th & Eads 12.0 B 8.5 A 14.0 B 12.1 B
1Unsignalized Intersection
Overall, study intersections simulated comparably operate as expected when compared to the Synchro
analysis results. Deviations from Synchro are largely attributed to VISSIM using a measured delay rather
than a formulaic calculation as done in deterministic methodologies like Synchro. These minimum
deviations suggest that the existing a.m. and p.m. peak models are operating as expected. Appendix B
contains the complete set of operational results and model output data for existing conditions.
26
EXISTING CONDITIONS FINDINGS
The operational analysis of existing traffic conditions identified several intersections and movements
that experience long queues, traffic congestion, and turning movements that operate at LOS F.
Army Navy Road/Eads Street
o Eastbound left-turn movement operates at LOS F during p.m. peak hour.
12th Street / Hayes Street
o Southbound left-turn movement operates at LOS F during a.m. peak hour.
Army Navy Road/12th Street
o The critical movement at the Army Navy Drive and 12th Street intersection is the
southbound left-turn, which operates at LOS F during the a.m. peak hour. This is due to
a combination of factors including southbound left-turn demand and a limited number
of gaps in traffic on eastbound 12th Street because of traffic volumes. The vehicle delays
contribute to queue build-up, which was determined from the VISSIM simulation to be
nearly 766 feet at the maximum simulated measurement during the a.m. peak hour.
o Field observation indicates that the southbound left-turning vehicles generally perform
a “rolling” stop when there’s no opposing traffic (most do not fully stop). The queue
accumulates pretty quickly from a platoon of eastbound vehicles arriving at the stop bar
when a pedestrian or a vehicle on 12th is using the intersection, but then the queue is
processed pretty readily. Vehicles do not make a full-stop and just slow down and treat
the stop sign as a yield sign. The developed simulation model well captured drivers’
behavior at this location and reflected the actual operational conditions.
o These results correspond well to visual observations of queuing during field visits. Traffic
congestion and queuing at this intersection is substantially less during the p.m. peak
hour.
Army Navy Drive/Hayes Street
o Southbound left-turning queues of approximately 1,085 feet were observed to extend
back on the off-ramp during the weekday a.m. peak hour. The queue was observed to
increase as demand on the eastbound approach of I-395 increased. No queue spill-back
onto the freeway was observed during the simulation.
o In short, both a.m. and p.m. scenarios indicate that the queues at southbound Hayes
Street can be accommodated within the existing off-ramp storage capacity. The a.m.
peak period experiences the longest queues from the freeways.
General findings
o Simulation results match with the field observations of queues and driver behavior.
o All intersections simulated comparably operate as expected when compared to the
Synchro analysis results.
SECTION 4
Travel Demand Modeling
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TRAVEL DEMAND MODELING
The Metropolitan Washington Council of Governments’ (MWCOG) travel demand model was used in
this study as a tool for projecting future traffic volumes for the Army Navy Drive Traffic Study.
Modifications were made, driven by validation assessments, to the model network within the Army
Navy Drive study area in order to improve the accuracy of the model output. This resulted in the model
output more adequately reflecting conditions in the field. The traffic volumes forecast by the modified
model in the base year of 2015 compare favorably with the turning movement counts in the field. Such
measures of model performance as the percentages of differences in volumes and the root-mean
square estimate (RMSE) of the modified model are much better than the original model. An NCHRP 255
analysis was then conducted to develop turning-movement volumes for more in-depth traffic
operations evaluation for the 2020 and 2040 conditions This section provides a summary of the model
modifications, the future year model (2020 and 2040) conditions and the results of the NCHRP 255
analysis.
NETWORK MODIFICATIONS – 2015 MODEL
Numerous inconsistencies were found in the 2015 travel demand model, including incorrect number of
travel lanes, improper coding of links (e.g., incorrect link connections or links coded at incorrect places),
Traffic Analysis Zones (TAZs), and centroid connectors. The MWCOG model network also did not include
some key links needed for the Army Navy Drive study area. KAI added or extended individual streets so
that relevant study intersections and links would be represented in the network. By applying these
modifications, the network in the study area more-closely represented the actual highway network.
The network modifications were then tested for the 2015 base year. Once a satisfactory validation was
obtained, these were applied to the 2020 and 2040 model networks. The detailed summary of the
network modifications is attached in Appendix B. Figure 10 shows the modified MWCOG model
network of the Army Navy Drive study area. Figure 11 shows the original MWCOG model network of
the Army Navy Drive study area.
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Figure 10 – Modified Network in Army Navy Drive Study Area
31
Figure 11 – Original Network in Army Navy Drive Study Area
The changes made to the network significantly improved the comparison of the 2015 model output for
the a.m. and p.m. peak hours with the field counts (i.e., traffic turning movement counts). The detailed
output model volumes in the study area are attached in Appendix D. Table 5 summarizes the total link
volume differences and the RMSE for the Army Navy Drive study corridor (i.e., Army Navy from S Joyce
St and 12th St S) for the a.m. peak hour and p.m. peak hour, respectively. As shown in the table, the
total model volume in the modified model is close to the turning movement counts (within 5% range).
The percentage of difference and RMSE of the modified model are much better than the original model.
The link-level comparisons of model volumes and field measurements are attached in Appendix E.
Table 5 Two-way Volume Comparison for Army Navy Drive
Peak Hour Field Count
Original Model Modified Model
Model Volume Percent %RMSE Model Volume Percent %RMSE
AM 16,349 11,291 -31% 71% 17,141 5% 39%
PM 17,942 13,102 -27% 52% 17,484 -3% 29%
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Although the final fit between the model volumes and the counts is much improved, some movements
at individual intersections are still significantly off from the field observations. Therefore, the NCHRP
255 method was used later to develop the VISSIM inputs instead of directly using the volume
forecasted by the regional travel demand model. Based on the link volumes forecasted by the regional
travel demand model, growth rates were calculated through the NCHRP 255 method and the growth
rates were then applied on the corresponding field observations to forecast the future conditions.
It should be noted that the MWCOG travel demand model only produces peak period (a.m. and p.m.)
traffic volumes. The peak hour traffic volumes used in this study were calculated based on the peak-
hour factors suggested by the MWCOG travel demand model: 41.7% for the a.m. peak hour and 29.4%
for the p.m. peak hour. The project team also calculated the peak-hour factors (i.e., peak hour
volume/peak period volume) based on two tube-count locations on Army Navy Drive (between S Hayes
Street and S Fern Street, and between S Eads Street and 12th Street S). This was done in order to
validate the values suggested by the model. According to the tube counts, the corresponding peak hour
factors are 42.0% (average of 39% and 45%) for a.m. peak hour and 29.0% (average of 28% and 30%)
for p.m. peak hour. This correlates well with the values used in the MWCOG travel demand model.
STUDY AREA CONDITIONS – 2020 MODEL
As previously stated, the network modifications applied in the 2015 model above were also included in
the 2020 model network. The detailed 2020 model volumes in the study area are attached in Appendix
E. In order for more in-depth traffic operations evaluation for the 2020, turning movement counts were
developed using the NCHRP 255 procedure for the intersections along Army Navy Drive. These turning
movement volumes were then adjusted for analysis purposes in the following ways:
Traffic volumes were rounded to the nearest five vehicles per hour;
Traffic volumes were balanced between each pair of adjacent intersections; and,
In cases where existing volumes exceeded the developed NCHRP 255 volumes, the existing
volumes were used for analysis (i.e. all volumes were assumed to either increase or remain
unchanged between the existing year and 2040).
Appendix E summarizes 2020 model volumes and the corresponding turning-movement volumes
developed by the NCHRP 255 procedure for a.m. peak hour and p.m. peak hour, respectively.
STUDY AREA CONDITIONS – 2040 MODEL
As with the 2020 model, the network modifications applied in the 2015 model were applied to the 2040
model network. The 2040 turning-movement volumes of the intersections along Army Navy Drive were
also developed using the NCHRP 255 procedure. The detailed 2040 model volumes in the study area are
attached in Appendix E.
SECTION 5
Design Concept Refi nement
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DESIGN CONCEPT REFINEMENT
INITIAL DESIGN CONCEPT
The initial Design Concept called for improvements to Army Navy Drive between Joyce Street and 12th
Street including:
Median transit lanes between Joyce Street and Hayes Street.
Protected bike lanes on the south side of Army Navy Drive from Joyce Street to 12th Street.
Incorporation of a transit facility between Joyce Street and the Parking Garage Driveway.
INITIAL OBSERVATIONS
KAI conducted an initial screening of the concept, and developed a list of observations to consider prior
to modeling (as depicted in Figure 12). These included transit (blue), vehicular (red), bicycle (green),
and pedestrian (yellow) considerations. Major takeaways included:
Bicycle treatments should be further evaluated to address the following observations:
o Conflicts could exist between bicycle movements and other modes at the
intersections, requiring exclusive bicycle phases.
o The location of the protected bike lanes could cause confusion for inexperienced
cyclists attempting to enter and exit the facility.
o Conflicts between right-turning vehicles and bicyclists in the protected bike lanes
could exist.
The median transit lanes should be further evaluated to address the following observations:
o Conflicts could exist between bus movements and other modes at the intersections,
requiring exclusive transit phases.
o Mixed traffic could accidentally enter the median transit lanes, particularly at Joyce
Street and Hayes Street where buses would be turning into and out of the lanes.
o Transit stops located in the median could cause confusion for riders.
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Figure 12 – Initial Design Concept Considerations
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BICYCLE TREATMENTS
Based on initial observations, consideration was given to moving the protected bike lanes to the north
side of Army Navy Drive or into the median (in place of the transit lanes). However, the decision was
made to keep the protected bicycle lanes on the south side of the corridor for the following reasons:
Keeping the protected bike lanes on the south side of Army Navy Drive (versus the north
side) provides easier access to the major commercial developments in the area.
Having the protected bike lanes on the south side of the corridor (versus the median) also
provides flexibility with the signal equipment. It allows bicyclists moving into and out of the
facility to progress with vehicular traffic without the use of bicycle signal heads and
exclusive bicycle phases. Conflicts between bicycles and other modes can be reduced
through the use of bike boxes.
The observations related to conflicts between bicycles and other modes should be fully resolved in the
design phase. Guidance will be required for bicyclists as well as other modes as they interact with the
protected bike lanes.
The remainder of the operational analysis was conducted assuming that the protected bike lanes will be
located on the south side of Army Navy Drive.
TRANSIT TREATMENTS
Two concepts were ultimately evaluated for the exclusive transit lanes – (1) median transit lanes and (2)
outside transit lanes. Both concepts were evaluated using critical movement analysis for existing a.m.
and p.m. volumes. Critical movement analysis not only provided insights into the potential conflicts at
the intersections, but also provided an estimated cycle length that would be required to accommodate
demand. This type of analysis is only planning-level, and many assumptions (outlined in Appendix F)
had to be made; critical movement analysis was beneficial because it provided a quick method for
comparing the alternatives.
As expected from the initial observations, there were many conflicts between buses and other modes
when considering the median transit lanes. These conflicts required exclusive transit phases, which
increased cycle lengths, as well as lane-configuration revisions at some of the intersections. In order to
fully vet the concept, outside transit lanes were also evaluated.
While a full assessment of all five intersections in the study area was completed (available in Appendix
F), this section focuses on Joyce Street, the Parking Garage Driveway, and Hayes Street. The concepts
remain the same at Fern Street and Eads Street, so those intersections had less influence on the
location of the transit facility.
38
Median-Transit-Lanes Concept
In addition to the location of the transit lanes, a decision had to be made about which buses would use
the transit lanes. There are high-capacity buses that run along Army Navy Drive. These travel to/from
the north leg of Joyce Street, turn onto Army Navy Drive, and travel to/from the south leg of Hayes
Street. In order for the exclusive transit lanes to be most effective, all buses along the corridor would
need to utilize them (not just the high-capacity buses).
However, several scenarios were evaluated using critical movement analysis, in order to assess the
effect of high-capacity buses versus all buses using the transit facility:
Median-transit-lanes concept with high-capacity buses
Median-transit-lanes concept with all buses
Revised lane configuration with high-capacity buses
Revised lane configuration with all buses
The revised-lane-configuration scenarios incorporate changes at several intersections to reduce
conflicts between modes and ultimately decrease the required cycle length. Revisions included in these
scenarios are listed in Table 6.
Table 6 Lane-Configuration Revisions for Median-Transit-Lanes Concept
Intersection Lane-Configuration Revision Reason for Recommended Change
Parking Garage Driveway
Changed eastbound approach to left and through-right lanes (instead of left-through and through-right lanes)
Left-turn lane is required unless split phasing is used on the eastbound and westbound approaches
Changed northbound approach to left, through, and dual right lanes (instead of left, left-through, and right lanes)
Using left and through lanes is better for driver expectations
Dual right-turn lanes reflect existing conditions at the parking garage
Changed southbound approach to left and through-right lanes (instead of left-through and right lanes)
Using left and through-right lanes is better for driver expectations
Hayes Street Reversed right-turn lane and bike lane (so that bike lane is on the outside)
With the protected bike lanes on the south side of Army Navy Drive, weaving would occur between vehicles and bicycles with the right-turn lane on the outside
Table 7 summarizes the increase or decrease in cycle length that would be required to accommodate
demand during the a.m. and p.m. peaks for each of the scenarios. Most of the scenarios require an
increase in cycle length to accommodate demand. This is expected because the number of through
lanes along the corridor has been reduced to provide space for the exclusive transit lanes.
Most likely, median transit lanes would have all buses using the facility (as shown in Figure 13, Figure
14, and Figure 15) and would require lane-configuration revisions. In particular, revisions would be
required at the Parking Garage Driveway. Without left-turn lanes, the eastbound and westbound
movements would have to be split phase, so that left-turning vehicles would not conflict with buses in
the exclusive transit lanes. This drives the cycle length up to nearly 180 seconds in the p.m. peak (using
39
only existing volumes). In order to provide a more-reasonable cycle length, eastbound and westbound
left-turn lanes would be required. However, this would reduce the eastbound through movement to
one lane.
Table 7 Estimated Cycle-Length Increase or Decrease (in Seconds Compared to Existing Conditions) Required to Accommodate Demand with Median Transit Lanes
Concept
Joyce Street Parking Garage Driveway Hayes Street
AM PM AM PM AM PM
Existing Condition 100 100 100 100 100 100
Median-Transit-Lanes Concept with High-Capacity Buses +14 +10 +57 +77 +45 +43
Median-Transit-Lanes Concept with All Buses +31 +29 +57 +77 +69 +73
Revised Lane Configuration with High-Capacity Buses +14 +10 +6 -11 +45 +43
Revised Lane Configuration with All Buses +31 +29 +6 -11 +69 +73
Figure 13 – S Joyce Street Median Transit-Lanes Concept Movements
40
Figure 14 – Parking Garage Driveway Median-Transit-Lanes Concept Movements
Figure 15 – S Hayes Street Median-Transit-Lanes Concept Movements
41
Outside-Transit-Lanes Concept
Reducing the eastbound through movement down to one lane, as required in the median-transit-lanes
concept, may not be possible because of queuing. An outside-transit-lanes concept was assessed to
determine if major lane-configuration revisions could be avoided. Again, several scenarios were
evaluated using critical movement analysis:
Outside-transit-lanes concept with high-capacity buses
Outside-transit-lanes concept with all buses
Revised lane configuration with high-capacity buses
Revised lane configuration with all buses
The revised-lane-configuration scenarios incorporate changes at several intersections to reduce
conflicts between modes and ultimately decrease the required cycle length. Revisions included in these
scenarios are listed in Table 8.
Table 8 Lane-Configuration Revisions for Median-Transit-Lanes Concept
Intersection Lane-Configuration Revision Reason for Recommended Change
Parking Garage Driveway
Changed northbound approach to left, through, and dual right lanes (instead of left, left-through, and right lanes)*
Using left and through lanes is better for driver expectations
Dual right-turn lanes reflect existing conditions at the parking garage
Changed southbound approach to left and through-right lanes (instead of left-through and right lanes)*
Using left and through-right lanes is better for driver expectations
Hayes Street Reversed right-turn lane and bike lane (so that bike lane is on the outside)
With the protected bike lanes on the south side of Army Navy Drive, weaving would occur between vehicles and bicycles with the right-turn lane on the outside
*Lanes have since been reconfigured for the ultimate concept; see Geometric Recommendations for details.
Unlike the median-transit-lanes concept, the outside-transit-lanes concept assumes that the transit
lanes will be shared with right-turning vehicles. Therefore, only high-capacity buses will likely utilize the
transit facility; other buses (not turning to/from the north leg at Joyce Street or the south leg at Hayes
Street) will utilize the traditional travel lanes. If all buses were to use the transit facility, right-turning
vehicles could experience long delays waiting behind buses requesting exclusive transit phases. Transit
will still be receiving a benefit from the right-turn-only/transit lanes, but the benefit will not be as high
as with exclusive transit lanes.
Table 9 summarizes the increase or decrease in cycle length that would be required to accommodate
demand during the a.m. and p.m. peaks for the four scenarios listed above. The values that are less
than those under the median-transit-lanes concept are highlighted in green. It is clear from the table
that significant benefit can be achieved at the Parking Garage Driveway with the outside transit lanes.
This concept allows buses to travel with vehicular traffic because left-turning vehicles do not conflict
with through bus movements.
42
Most likely, outside transit lanes would have only high-capacity buses using the facility (as shown in
Figure 16, Figure 17, and Figure 18) and would not require lane-configuration revisions to reduce the
cycle length. Ring-and-barrier diagrams for this concept (for Joyce Street, the Parking Garage Driveway,
and Hayes Street), developed in preparation for modeling, are shown in Figure 19, Figure 20, and Figure
21.
Table 9 Estimated Cycle-Length Increase or Decrease (in Seconds Compared to Existing Conditions) Required to Accommodate Demand with Outside Transit Lanes
Concept
Joyce Street Parking Garage Driveway Hayes Street
AM PM AM PM AM PM
Existing Condition 100 100 100 100 100 100
Outside-Transit-Lanes Concept with High-Capacity Buses +14 +10 +40 +29 +45 +43
Outside-Transit-Lanes Concept with All Buses +31 +27 +40 +29 +69 +73
Revised Lane Configuration with High-Capacity Buses +14 +10 -4 -11 +45 +43
Revised Lane Configuration with All Buses +31 +27 -4 -11 +69 +73
Note: Table cells highlighted in green represent values that are lower with outside transit lanes than with median transit lanes.
Figure 16 – S Joyce Street Outside-Transit-Lanes Concept Movements
43
Figure 17 – Parking Garage Driveway Outside-Transit-Lanes Concept Movements
Figure 18 – S Hayes Street Outside-Transit-Lanes Concept Movements
44
Figure 19 – Joyce Street AM (left) and PM (right) Ring-and-Barrier
Figure 20 – Joyce Street AM (left) and PM (right) Ring-and-Barrier
45
Figure 21 – Hayes Street AM (left) and PM (right) Ring-and-Barrier
QUALITATIVE EVALUATION
While the results of the critical movement analysis are a key component of the Design Concept
evaluation, there were several other metrics used to assess the advantages and disadvantages of the
transit facility concepts. Table 10 summarizes the evaluation criteria used to qualitatively assess
whether a slight or significant advantage was anticipated with median or outside transit lanes. The
following categories were assessed:
Vehicle operations
Transit operations
Conflicts at intersections
Conflicts along segments
User expectations at intersections
User expectations along segments
46
Table 10 Evaluation of Median and Outside Transit Lanes
Evaluation Criteria
Median Transit Lanes
Outside Transit Lanes Notes
Vehicle Operations ✔
Fewer transit-only phases are required with outside transit lanes (particularly at the Parking Garage intersection), which results in more time for other vehicles during the cycle.
Combining the transit and right-turn lanes on the outside allows extra cross-section space to be used for other movements, increasing capacity for vehicles in those lanes.
Transit Operations ✔ Inside transit lanes are exclusive transit lanes, resulting in more-reliable travel times
for buses (i.e. more-consistent headways).
However, with outside transit lanes, transit can run concurrently with additional vehicle movements, meaning transit receives more green time during the cycle.
Minimize Conflicts at Intersections ✔
Buses using outside transit lanes conflict with fewer vehicle movements at intersections. In other words, outside transit can run concurrently with adjacent left-turning, through, and right-turning traffic, but inside transit must often utilize a transit-only phase.
Inside transit lanes create the potential for vehicles to accidentally turn into the transit lanes, which are median-separated.
Minimize Conflicts Along Segments ✔
Outside transit lanes create the potential for weaving maneuvers into and out of the right-turn-only/transit lanes.
Buses using outside transit lanes may block other drivers’ view of contraflow bicycles.
User Expectations at Intersections ✔
Bus drivers would be making atypical movements from inside transit lanes, requiring transit-only signals.
Inside transit lanes would require guidance to prevent vehicles from following buses into the transit lanes.
User Expectations Along Segments ✔
Outside transit lanes would allow for more-conventional, curbside bus stops.
OVERALL ✔
LEGEND ✔ = Significant Advantage ✔ = Slight Advantage
CONCEPT REFINEMENT
Based on the results of the critical movement analysis and qualitative evaluation, the County decided
that the outside-transit-lane concept should be modeled. The following changes were made to the
initial Design Concept:
Transit lanes were moved to the outside lanes between Joyce Street and Hayes Street.
Transit lanes will also serve right-turning vehicles by restricting through vehicles (except for
buses) at the intersections.
Bicyclists leaving the protected bike lanes on the south side of Army Navy Drive from Joyce
Street to 12th Street will utilize bike boxes and run concurrently with vehicular traffic.
Some of the additional lane-configuration revisions listed in Table 8 were not incorporated into the
revised concept but should be considered in the design phase.
SECTION 6
Future Conditions Analysis
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FUTURE CONDITIONS ANALYSIS
Understanding how implementing the Design Concept will affect traffic conditions in the future aids in
identifying potential flaws in the design that would not be captured under current conditions.
Background developments within the study area were also considered. It should be noted that the I-395
HOT lanes and associated improvements were not included in the analysis.
BACKGROUND DEVELOPMENTS
For future year analyses, background infrastructure and land-use developments were included to
account for their impact to the traffic network. Future planning accounts for the completion of 12th
Street S between Fern Street and Eads Street and there are three notable developments anticipated to
affect the Study: the Pentagon Transit Center, PenPlace, and 400 Army Navy Drive. Figure 22 shows the
locations of these developments within the study area. Site plans for all developments can be found in
Appendix G.
Figure 22 – Location of Background Developments
12th Street Completion/Transit Facility
The most notable infrastructure improvement is the completion of the 12th Street South alignment
between Fern Street and Eads Street, which had not been constructed at the time this study began
(construction completed in 2016). This connection has been modeled as a two-lane cross-section
(consistent with the blocks on either end). In addition to the connection between Fern Street and Eads
Street, 12th Street S was modified to accommodate a proposed median bus lane facility between Eads
Street and Clark Street, requiring Army Navy Drive/12th Street S to be signalized. This facility assumed a
50
single median transit lane and single all-traffic lane in each direction. Intersections at Eads Street and
Army Navy Drive were reconfigured to accommodate bus-only signal phasing, allowing buses to re-
integrate with traffic outside of the new bus facility. Details regarding the proposed configuration of
12th Street and the modeled signal phasing timing are included in Appendix I.
Pentagon Transit Center
The Pentagon and WMATA are developing a transit center at the northeast corner of S Joyce St/Army
Navy Drive. The transit center is in preliminary design by internal Pentagon staff. The current plans
show and 8-bay sawtooth design with the access to the center being directly adjacent to the Army Navy
Drive travel lanes. The operation of this center is currently under development, but is considered to be
used by WMATA, ART, commuter bus routes, and tourist buses.
PenPlace
Vornado/Charles E. Smith is in the process of developing a commercial complex, referred to as
PenPlace, just south of Army Navy Drive between Fern Street and Eads Street (Reference 3). The
PenPlace development is intended to retain the existing Marriott Residence Inn in the northwest
portion of the site and proposes four new office buildings and a hotel. The development fronts the
newly constructed connection of 12th Street South between Fern Street and Eads Street and an
additional two east-west access driveways. The total development anticipates adding 149 a.m. peak
trips (47 in, 102 out) and 235 p.m. peak trips (131 in, 104 outs).
400 Army Navy Drive
The site at 400 Army Navy Drive (positioned at the southeast corner of Army Navy Drive/S Eads St) is
planned for redeveloping the existing 235,000 square-foot office building with a 452 unit multi-family
residential development (Reference 4). The redevelopment does not propose the construction of any
new access driveways onto Army Navy Drive or S Eads St. The total development anticipates reducing
the total number of a.m. and p.m. peak hour trips due to the change in land use from commercial office
to multi-family residential.
YEAR 2020 AND 2040 NO-BUILD
No-build scenario was developed and analyzed to forecast how the study network would operate at the
future planning horizon without the implementation of the Design Concept. Figure 23 shows the no-
build condition lane configuration and traffic control devices at the study intersections as modeled;
analysis began in 2015 prior to completion of 12th Street South. Figure 24 and Figure 25 summarize the
delay and LOS results for the study intersections during the weekday a.m. and p.m. peak periods under
2020 traffic conditions. Figure 26 and Figure 27 detail the 2040 no-build traffic operations results.
56
With increasing traffic demand in the year 2020 and 2040, traffic performance within the study area
will deteriorate. Individual intersection operations will vary from time period to time period due to
changes in traffic demands and adjustment to signal timing/phasing between future Years 2020 and
2040 (i.e. it is unlikely to see a consistent change in operations intersection-to-intersection between
analysis years). Under the no-build condition, congestion along Army Navy Drive is anticipated to
mostly be concentrated toward the east side of the corridor and focused around the Eads Street/Army
Navy Drive intersection. For both peak hours, Eads Street/Army Navy Drive is anticipated to operate at
LOS E/F in both Year 2020 and Year 2040. It is this center of congestion that spills to neighboring
intersections and is largely limited by the capacity of the vehicle trips destined northbound toward the
north I-395 on-ramp. Heavy eastbound left demands conflicting with heavy westbound through
demands (from the US 110 off-ramp and westbound Army Navy Drive traffic) result in limited protected
green time. All 2020 and 2040 no-build traffic operations results can be found in Appendix H. Overall
intersection operations are summarized in Table 12 and Table 13.
The operational analysis of no-build traffic conditions in Year 2020 identified intersection approaches
that continue experiencing long queues and traffic congestions that operate at LOS E or worse, which
are summarized below:
S Hayes Street/ Army Navy Drive
o Eastbound approach will operate at LOS F during the p.m. peak hour, driven by left- and
through- traffic demands.
o Northbound and southbound approaches will operate at LOS E during the a.m. peak
hour due to heavy left-turn volumes only being serviced by protected phases.
S Fern Street/Army Navy Drive
o Northbound approach will operate at LOS E during a.m. and p.m. peak hours, driven by
high left-turn demand as a side street.
o Eastbound approach will operate LOS E during the p.m. peak hour due to queue
spillback from Eads Street/Army Navy Drive limiting throughput.
S Eads Street/Army Navy Drive
o The overall intersection will operate at LOS E during the a.m. peak hour and LOS F
during the p.m. peak hour.
o Eastbound approach will operate at LOS F during a.m. and p.m. peak hours. Heavy left-
turn movement causes queue spillback along the approach and is unable to recover
within the peak hour. The shared left-through configuration also limits the capacity of
through vehicles.
o Westbound approach will operate at LOS F during the p.m. peak hour. Heavy demand
from the westbound approach conflicts with the eastbound left and needs to compete
for available green time with limited available geometric capacity.
o Southbound approach operates at LOS F during a.m. peak hour due to limited side-
street green time available.
o Northbound approach operates at LOS F during the p.m. peak hour due to limited side-
street green time and a single lane approach to Army Navy Drive.
Army Navy Drive/12th Street S
57
o Congestion at this intersection is largely attributed to several factors: 1. All movements are designed to keep traffic flowing through two intersections
along 12th Street South (at Army Navy Drive and at Clark Street), requiring longer clearance intervals.
2. All movements have limited flexibility in allowable green time due to the two-intersection phasing.
3. The intersection (in conjunction with 12th Street S/Clark Street) has heavy relatively heavy turning volumes compared to through-volumes.
o The overall intersection will operate at LOS F during the a.m. and p.m. peak hours. o Eastbound approach will operate at LOS F during the a.m. peak hour. o Westbound approach will operate at LOS F during the a.m. and p.m. peak hours. o Southbound approach will operate at LOS E and over capacity during the a.m. peak
hour.
Noteworthy operational observations in the Year 2040 under no-build conditions include:
S Joyce Street/Army Navy Drive
o Eastbound approach will operate at LOS E during the a.m. peak hour due to heavy
demand for all movements.
Pentagon Mall Garage/Army Navy Drive
o The overall intersection will operate at LOS E during the a.m. peak hour.
o Westbound approach will operate at LOS F during the a.m. peak hour due to heavy left-
turn demands into the parking garage.
S Hayes Street/Army Navy Drive
o The overall intersection will operate at LOS E during the a.m. peak hour.
o Eastbound approach will operate at LOS E during the p.m. peak period due to heavy left-
turn and through demand. The left-turn movement (toward I-395) is only processed
during a protected phase.
o Northbound approach will operate at LOS F during the a.m. peak period due to heavy
left-turn demand limited by a protected-only phase.
o Southbound approach will operate at LOS F/E during the a.m. and p.m. peak hours,
respectively. Heavy overall demand is the primary cause for high delays during the a.m.
peak hour. Heavy relative left-turn demand is the main cause during the p.m. peak hour.
S Fern Street/Army Navy Drive
o The overall intersection will operate at LOS E during the p.m. peak hour.
o Northbound approach will operate at LOS F during a.m. and p.m. peak hours, driven by
high overall demand as a side street.
o Eastbound approach will operate LOS F during the p.m. peak hour due to queue
spillback from Eads Street/Army Navy Drive limiting throughput.
S Eads Street/Army Navy Drive
o The overall intersection will operate at LOS E during the a.m. peak hour and LOS F
during the p.m. peak hour.
58
o Eastbound approach will operate at LOS F during a.m. and p.m. peak hours. Heavy left-
turn movement causes queue spillback along the approach and is unable to recover
within the peak hour. The shared left/through configuration also limits the capacity of
through vehicles.
o Westbound approach will operate at LOS F during the p.m. peak hour. Heavy demand
from the westbound approach conflicts with the eastbound left and needs to compete
for available green time with limited available geometric capacity.
o Northbound approach operates at LOS F during the p.m. peak hour due to limited side
street green time and a single lane approach to Army Navy Drive.
Army Navy Drive/12th Street S
o Congestion at this intersection is largely attributed to several factors: All movements are designed to keep traffic flowing through two intersections
along 12th Street S (at Army Navy Drive and at Clark Street), requiring longer clearance intervals.
All movements have limited flexibility in allowable green time due to the two-intersection phasing.
The intersection (in conjunction with 12th Street S/Clark Street) has heavy relatively heavy turning volumes compared to through-volumes.
o The overall intersection will operate at LOS E during the a.m. peak hour and LOS F during the p.m. peak hour.
o Eastbound approach will operate at LOS F during the a.m. peak hour. o Westbound approach will operate at LOS F during the a.m. and p.m. peak hours. o Southbound approach will operate at LOS E and over capacity during the a.m. and p.m.
peak hours.
General findings from peak hour operations in no-build conditions include:
Significant congestion was observed in both future years during both a.m. and p.m. peak
hours, notably at S Hayes Street, S Fern Street, S Eads Street and 12th Street intersections.
Queue storage on the southbound S Hayes Street approach (I-395 ramp) is accommodated
through 2040 for both a.m. and p.m. peak hours.
The observed bottleneck is the eastbound approach at S Eads Street/Army Navy Drive.
Current eastbound lane configuration is a left/through and through/right layout, which
negatively impacts the progression of left-turn and through movements. Future forecast
indicates heavy demands from all legs combined at this intersection with predominate
conflicts between eastbound left-turn movement and westbound through movement. With
heavy volumes destined to the northbound direction towards I-395, the limitation of having
a single receiving lane, congestion is not expected to be alleviated using only signal
timing/phasing improvements.
59
YEAR 2020 AND 2040 BUILD
Build scenario models were developed to account for both background development and the
implementation of the Design Concept. Figure 28 shows the future planning lane configuration and
traffic control devices at the study intersections. Figure 29 and Figure 30 show delay and LOS results for
the study intersections during the Year 2020 peak hours. Figure 31 and Figure 32 detail the 2040 build
traffic operations results.
The build condition limits capacity compared to the no-build condition by limiting the number of traffic
lanes that can be utilized by general traffic in favor of transit and bicycle facilities. Under build
conditions, the study network experiences notable increases in per-vehicle delay compared to existing
conditions as well as no-build conditions. This varies intersection-to-intersection, but is attributed to
the limited capacity from travel lanes being repurposed and subsequent signal timing/phasing
constraints. The most impacted intersections include: S Hayes Street, S Fern Street, S Eads Street and
12th Street, which generally exhibit a decrease in LOS from LOS D to LOS E/F during the peak hours.
Significant congestions in the build scenarios were observed resulting in extensive queues and cycle
failures along Army Navy Drive. All 2020 and 2040 build traffic operations results can be found in
Appendix H. Overall intersection operations are summarized in Table 12 and Table 13.
The operational analysis of build traffic conditions in Year 2020 identified intersection approaches that continue experiencing long queues and traffic congestions that operate at LOS E or worse, which are summarized below:
Pentagon Mall Garage/Army Navy Drive
o Westbound approach will operate at LOS F during the p.m. peak hour due to heavy-left
turn demands into the parking garage.
S Hayes Street/Army Navy Drive
o The overall intersection will operate at LOS E during the a.m. peak hour. o Eastbound approach will operate at LOS F during the a.m. peak hour due to heavy
through and right-turn volumes. Northbound approach will operate at LOS E due to high-left turn delay, limited by a protected only phase and heavy demand.
o Southbound approach will operate at LOS F during the a.m. peak hour. The a.m. peak hour delays are due to high overall demand on the approach.
S Fern Street/Army Navy Drive
o Westbound approach will operate at LOS E during the p.m. peak hour from overall heavy demand.
o Northbound approach will operate at LOS E during the a.m. peak hour and LOS F during the p.m. peak hour driven by high overall demand as a side street.
S Eads Street/Army Navy Drive
o The overall intersection will operate at LOS F during the p.m. peak hour. o Westbound approach operates at LOS F during the p.m. peak hour due to heavy through
demand competing with the conflict eastbound left-turn demand.
60
o Northbound and southbound approaches operate at LOS E/F during both a.m. and p.m. peak hours due to high overall demand as a side street. The northbound approach is limited due to the single lane along the approach and heavy left-turn movement spilling back.
Army Navy Drive/12th Street S
o Congestion at this intersection is largely attributed to several factors: All movements are designed to keep traffic flowing through two intersections
along 12th Street South (at Army Navy Drive and at Clark Street), requiring longer clearance intervals.
All movements have limited flexibility in allowable green time due to the two-intersection phasing.
The intersection (in conjunction with 12th Street S/Clark Street) has heavy relatively heavy turning volumes compared to through-volumes.
o The overall intersection will operate at LOS E during the a.m. peak hour and LOS F during the p.m. peak hour.
o Eastbound approach will operate at LOS F during the a.m. peak hour.
o Westbound approach will operate at LOS F during the a.m. and p.m. peak hours.
o Southbound approach will operate at LOS E during the a.m. peak hour.
Noteworthy operational observations in the Year 2040 under build conditions include:
S Joyce Street /Army Navy Drive
o Westbound approach will operate at LOS E during the a.m. peak hour due to heavy left
turn demand limited by protected only phasing.
o Northbound approach will operate at LOS E during the p.m. peak hour due to high left
turn and through demands.
o Southbound approach will operate at LOS E during the a.m. peak hour due to high left
turn demand limited by protected only phasing.
Pentagon Mall Garage/Army Navy Drive
o The overall intersection will operate at LOS E during the a.m. peak hour
o Westbound approach will operate at LOS F during the a.m. peak hour due to heavy left
turn demand limited by protected only phasing.
S Hayes Street/Army Navy Drive
o The overall intersection will operate at LOS F during the a.m. peak hour and LOS E
during the p.m. peak hour.
o Northbound approach will operate at LOS F during a.m. peak hour and LOS E during the
p.m. peak hour due to heavy left turn demand limited by protected only phasing.
o Southbound approach will operate at LOS F during the a.m. and p.m. peak hours due to
heavy left turn demand.
S Fern Street/Army Navy Drive
o The overall intersection will operate at LOS E during the p.m. peak hour.
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o Eastbound approach will operate at LOS E during the p.m. peak hour due to queue
spillback from Eads Street/Army Navy Drive limiting throughput.
o Westbound approach will operate at LOS E during the p.m. peak hour due to heavy left
turn and through demand.
o Northbound approach will operate at LOS F due to high overall demand as a side street.
S Eads Street/Army Navy Drive
o The overall intersection will operate at LOS E during the a.m. peak hour and LOS F
during the p.m. peak hour.
o Eastbound approach will operate at LOS F during the a.m. and p.m. peak hours. Heavy
left turn volumes limited by protected only phasing and heavy conflicting westbound
through volumes.
o Westbound approach will operate at LOS F during the p.m. peak hour. Heavy demand
from the westbound approach conflicts with the eastbound left and needs to compete
for available green time with limited available geometric capacity.
o Northbound approach operates at LOS E during the a.m. peak hour and LOS F during the
p.m. peak hour due to limited side street green time and a single lane approach to Army
Navy Drive.
o Southbound approach operates at LOS E during the a.m. and p.m. peak hours due to
high overall demand as a side street.
Army Navy Drive/12th Street S
o Congestion at this intersection is largely attributed to several factors: All movements are designed to keep traffic flowing through two intersections along
12th Street South (at Army Navy Drive and at Clark Street), requiring longer clearance intervals.
All movements have limited flexibility in allowable green time due to the two-intersection phasing.
The intersection (in conjunction with 12th Street S/Clark Street) has heavy relatively heavy turning volumes compared to through-volumes.
o The overall intersection will operate at LOS F during the a.m. and p.m. peak hours. o Eastbound approach will operate at LOS E during the a.m. and p.m. peak hours. o Westbound approach will operate at LOS E during the a.m. peak hour and LOS F during
the p.m. peak hour. o Northbound approach will operate at LOS E during the p.m. peak hour. o Southbound approach will operate at LOS F during the a.m. peak hour and LOS E during
p.m. peak hour.
General findings from peak hour operations in build conditions include:
Significant congestion was observed in both future years during both a.m. and p.m. peak
hours, notably at S Hayes Street, S Fern Street, S Eads Street, and 12th Street S intersections.
Queue storage on the southbound S Hayes Street approach (I-395 ramp) is accommodated
through 2040 for both a.m. and p.m. peak hours.
The observed network bottlenecks, like the no-build conditions are the S Eads Street/Army
Navy Drive intersection.
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o Future forecast indicates heavy demands from all legs combined at this intersection
with predominate conflicts between eastbound left-turn movement and westbound
through movement. With heavy volumes destined to the northbound direction towards
I-395, the limitation of having a single receiving lane, congestion is not expected to be
alleviated using only signal timing/phasing improvements.
o Queue storage along for the eastbound left-turn is recommended to be extended as far
as possible, but block spacing remains a limiting factor. Even with maximum storage,
left-turn queue spillback is anticipated.
The overall Design Concept limits capacity along Army Navy Drive, reducing general traffic
lanes in favor of transit and bicycle facilities.
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COMPARISON ACROSS ALL SCENARIOS
This section provides a comparison assessment of peak-hour operations of the study network across all
scenarios including: existing, no-build, and build conditions.
Network Wide Performance
The variability of signalized arterial networks makes analysis of individual intersections difficult to
evaluate overall traffic operations. Because intersections are closely spaced (generally around 600-ft,
stop bar-to-stop bar), a variety of factors affect individual intersection performance that may not be
indicative of actual traffic conditions, including:
Variations in signal timing/phasing;
Platoon progression, and;
Impacts of residual queues/queue spillback.
To better understand the operational impact of the Design Concept, network-wide performance
measures are examined including average delay, total travel times, and spot speeds. The following
section and graphs demonstrate these network level performance measures across the different
analyzed scenarios. The general trends show network performance decreases over time from existing
(2015) to future year conditions (2020 and 2040), producing increased vehicle delay, increased travel
time, and decreased spot speeds. Similar patterns were observed comparing no-build models to build
models in that the limited roadway capacity in the build model showed a decrease in network
performance compared to the accompanying no-build.
Average Network Delay
One parameter worth examining is the average network delay experienced by drivers under different
scenarios. Average network delay is calculated from the total delay measured in the study network
divided by the total user throughput. The total throughput can include all users, as shown in Figure 33,
or be refined to different vehicle classes like passenger cars (Figure 34) and transit (Figure 35).
Percentages above the bars in the graph indicate the percent change when comparing the build
scenario to the corresponding no-build scenario.
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Figure 33 – Average Network Delay for All Vehicles by Scenario
Comparing the impact of the build scenario, there is an estimated increase of approximately 7-27% in
average network delay for all vehicles (compared to the no-build scenario). Temporal comparisons
between Year 2020 and Year 2040 show an estimated increase of approximately 16-46% in average
network delay.
Figure 34 – Average Network Delay for Passenger Cars by Scenario
0
50
100
150
200
250
300
2015 2020 2040 2015 2020 2040
All All
AM PM
Ave
rage
De
lay
(se
c/ve
h)
No-Build Existing Build
0
50
100
150
200
250
2015 2020 2040 2015 2020 2040
Cars Cars
AM PM
Ave
rage
De
lay
(se
c/ve
h)
No-Build Existing Build
+7.3%
+26.9% +24.3%
+17.5%
-0.2%
+32.8%
+29.0%
+21.2%
70
Figure 35 – Average Network Delay for Transit by Scenario
Similar patterns follow when examining general traffic and transit-specific network-wide delay. The
transit delays increase in the build versus the no-build scenario and is further examined in the section
below.
Transit Route Travel Times
Examining more-specific travel times (particularly for transit) can help explain the impact of difference
scenarios to individual transit routes. Considering the multi-modal goals of the Design Concept,
examining these routes will provide better insight to the Design Concept’s efficacy of facilitating better
transit service.
Table 11 summarizes the transit travel times between S Joyce Street and S Eads Street during the peak
periods. Transit travel times generally increased in the build condition, despite the presence of a
dedicated lane.
0
50
100
150
200
250
300
2015 2020 2040 2015 2020 2040
Transit Transit
AM PM
Ave
rage
De
lay
(se
c/ve
h)
No-Build Existing Build
+16.6% +24.7%
+9.6%
+4.1%
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Table 11 Transit Travel Times
Direction Route AM Peak Hour
Existing 2020 No Build 2020 Build 2040 No Build 2040 Build
Eastbound Joyce to Hayes* 178.0 203.6 343.5 221.6 226.2
Hayes to Eads* 63.2 213.0 87.0 183.9 170.0
Westbound Eads to Hayes N/A N/A 157.2 N/A 182.9
Hayes to Joyce 93.1 118.2 112.0 131.4 145.3
Direction Route PM Peak Hour
Existing 2020 No Build 2020 Build 2040 No Build 2040 Build
Eastbound Joyce to Hayes 169.7 182.6 185.6 184.2 163.7
Hayes to Eads 130.3 274.7 103.0 298.3 247.2
Westbound Eads to Hayes* N/A N/A 168.8 N/A 171.5
Hayes to Joyce* 146.4 62.7 93.6 77.1 105.4
*indicates peak direction
Despite transit facilities being included under the build scenario, transit travel times increase with
transit-only lanes, specifically on the segments with those transit only lanes. This is attributed to the
Design Concept (and model) using these lanes as transit and right turns only. Figure 36 summarizes the
eastbound challenges with this situation as it terminates at S Hayes Street.
Figure 36 - Summary of Transit Travel Time Increases at S Hayes St/Army Navy Dr
What commonly happens is the following:
The EB right turns are delayed by cyclists and pedestrians, causing queues that extend to and beyond the near-side bus stop.
72
For buses departing the stop: EB queuing at the stop bar in adjacent through lanes block buses to the curbside lane; 20 buses during the a.m. peak hour need to merge to the adjacent through lane to continue EB (an additional 8 buses turn right during the a.m. peak hour).
For buses approaching the stop: The EB queues will extend beyond the bus stop, preventing buses from reaching to the near-side stop (first stop) until the standing queue clears the intersection. Then second stop occurs at the stop for boarding/alighting.
In other words, the transit lane is essentially a trap lane for over 70% of buses that continue EB on Army
Navy Drive, and the factors described above result in a notable increase in bus travel time. By contrast,
the no-build benefits from continuity of receiving lanes, and no conflicting cycle track. Some potential
mitigation strategies may include:
Relocating the bus stop further west to limit the extend of the queue or extending the bus stop platform to allow buses to dwell while getting blocked by the standing queue
Providing a receiving lane on the east side of S Hayes Street (which has its own limitations)
As a result, the transit only lanes only partially mitigate the impact of reducing the number of general
purpose traffic lanes. The transit only lanes are still recommended for implementation despite not
being able to maximize the potential benefit of continuous lanes from S Joyce Street through S Eads
Street.
Spot Speed
Spot speeds serve as a proxy measure of traffic flow at collected locations within the network. Rather
than the actual value of individual spot speeds, analyzing the “spread” of average spot speeds by
scenario can be an indication of each scenario’s impact to that particular location in the network. For
example, tightly clustered spot speed results indicate that there is little effect between scenarios at that
particular location. By contrast, a larger spread of average spot speeds (by scenario) would indicate a
particular location where the conditions of that scenario have a larger impact.
Figure 37 and Figure 38 show the simulation results of average spot speeds collected by scenario,
during the a.m. and p.m. peak hours, respectively. Generally, the congestion of the a.m. peak hour
seems to be relatively consistent across scenarios. The speed spreads during the p.m. peak hour,
indicating notable impacts of the Design Concept on the eastern side of the corridor (east of S Hayes
Street). No significant speed changes were observed along northbound Joyce Street or northbound S
Hayes Street during either peak hour.
73
Figure 37 – Spot Speeds during AM Peak Hour
Figure 38 – Spot Speeds during PM Peak Hour
Individual Intersection Performance
While network-wide performance measures can provide insight regarding the overall impact of a
scenario, examining individual intersection performance metrics can provide some detailed information
regarding network bottlenecks and challenges. Table 12, Table 13, Figure 39 and Figure 40 summarize
intersection control delay across all scenarios. Intersection-level performance metrics continue a trend
of worsening operations from existing to future conditions.
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
NB Joyce St SB Joyce St WB ArmyNavy Dr
(Hayes-Fern)
EB ArmyNavy Dr
(Hayes-Fern)
NB Hayes(AND-12th)
SB ArmyNavy Dr
(appr. 12th)
NB ArmyNavy Dr
(appr. 12th)
Sim
ula
tio
n S
pe
ed
(m
ph
)
Existing 2020 No-Build 2020 Build 2040 No-Build 2040 Build
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
NB Joyce St SB Joyce St WB ArmyNavy Dr
(Hayes-Fern)
EB ArmyNavy Dr
(Hayes-Fern)
NB Hayes(AND-12th)
SB ArmyNavy Dr
(appr. 12th)
NB ArmyNavy Dr
(appr. 12th)
Sim
ula
tio
n S
pe
ed
(m
ph
)
Existing 2020 No-Build 2020 Build 2040 No-Build 2040 Build
74
Future build scenario has significant operational impacts on the following intersections:
Army Navy Drive/S Hayes Street
Army Navy Drive/S Ferns Street
Army Navy Drive/S Eads Street
Army Navy Drive/12th Street
Table 12 Intersection Performances during AM Peak Hour
Intersection Existing (2015) 2020 No-Build 2020 Build 2040 No-Build 2040 Build
Delay LOS Delay LOS Delay LOS Delay LOS Delay LOS
Army Navy & Joyce 21.2 C 32.4 C 40.3 D 41.1 D 46.1 D
Army Navy & Parking Garage
24.0 C 39.2 D 50.2 D 60.7 E 56.1 E
Army Navy & Hayes 33.2 C 50.0 D 55.8 E 72.4 E 93.9 F
Army Navy & Fern 18.8 B 36.2 D 32.9 C 50.1 D 38.1 D
Army Navy & Eads 32.9 C 70.8 E 52.0 D 64.0 E 79.6 E
Army Navy & 12th 51.9 F 100.9 F 71.5 E 77.3 E 90.9 F
Joyce & North Driveway
19.6 C 8.2 A 7.1 A 8.5 A 7.9 A
12th & Hayes 30.6 C 16.9 B 8.9 A 16.9 B 9.9 A
12th & Fern 15.4 B 14.7 B 15.5 B 45.9 D 15.9 B
12th & Eads 12.0 B 26.7 C 12.6 B 31.0 C 15.6 B
Table 13 Intersection Performances during PM Peak Hour
Intersection Existing (2015) 2020 No-Build 2020 Build 2040 No-Build 2040 Build
Delay LOS Delay LOS Delay LOS Delay LOS Delay LOS
Army Navy & Joyce 24.7 C 19.5 B 35.3 D 19.9 B 42.6 D
Army Navy & Parking Garage
15.5 B 21.0 C 29.6 C 21.4 C 32.4 C
Army Navy & Hayes 26.2 C 45.7 D 38.1 D 49.6 D 62.8 E
Army Navy & Fern 23.2 C 54.8 D 47.9 D 60.2 E 79.6 E
Army Navy & Eads 42.1 D 113.7 F 93.2 F 115.5 F 138.0 F
Army Navy & 12th 11.4 B 93.7 F 121.3 F 251.8 F 240.3 F
Joyce & North Driveway
16.2 C 10.0 A 11.4 B 10.6 B 14.1 B
12th & Hayes 21.8 C 22.7 C 12.9 B 23.0 C 15.3 B
12th & Fern 17.4 B 25.4 C 25.0 C 33.9 C 33.6 C
12th & Eads 13.6 B 52.5 D 21.2 C 79.9 E 26.6 C
75
Figure 39 – Intersection Delay during AM Peak Hour
Figure 40 – Intersection Delay during PM Peak Hour
0.0
20.0
40.0
60.0
80.0
100.0
120.0
Army Navy &Joyce
Army Navy &Parking Garage
Army Navy &Hayes
Army Navy &Fern
Army Navy &Eads
Army Navy &12th
De
lay
(se
c/ve
h)
Existing 2020 No-Build 2020 Build 2040 No-Build 2040 Build
0.0
50.0
100.0
150.0
200.0
250.0
300.0
Army Navy &Joyce
Army Navy &Parking Garage
Army Navy &Hayes
Army Navy &Fern
Army Navy &Eads
Army Navy &12th
De
lay
(se
c/ve
h)
Existing 2020 No-Build 2020 Build 2040 No-Build 2040 Build
76
Queuing
Prevailing traffic patterns show eastbound being the peak direction during the a.m. peak period, while
westbound is the peak direction during the p.m. peak hour. Two significant locations where this occurs
is the southbound leg of S Hayes Street/Army Navy Drive and the Army Navy Drive approaches at S Eads
Street.
Southbound S Hayes Street at Army Navy Drive
The intersection at S Hayes Street/Army Navy Drive is of particular importance because of its
connection to I-395 and Washington Boulevard, with the southbound approach serving as the freeway’s
off-ramps to Army Navy Drive. A priority goal for the Design Concept must include mitigating queues on
this approach as to not spillback onto the freeway. Examining the full queue storage available on the
approach is shown in Figure 41.
Figure 41 – Measured Southbound Queue Storage at S Hayes Street/Army Navy Drive
The shortest queue storage is from Washington Blvd at 1,970 feet. This storage distance serves as the
threshold no maximum queue may extend past to be considered acceptable. Furthermore, because the
maximum modeled queues will, in reality, be divided between the I-395 ramp and Washington Blvd
ramp, the maximum queue distance on either ramp will always be less than the maximum queue
reported.
Table 14 summarizes the maximum simulated queues for southbound movements at S Hayes
Street/Army Navy Drive. Results from all scenarios anticipate long southbound queues but are
accommodated within the existing off-ramp storage across all scenarios.
Table 14 Maximum simulated Queues at Southbound Hayes Street/Army Navy Drive Intersection
SB Hayes Approach Storage (ft) 95th-Percentile Queue (feet)
AM Adequate Storage? PM Adequate Storage?
2020 No-Build 1970 1000 YES 900 YES
2020 Build 1970 950 YES 425 YES
2040 No-Build 1970 1300 YES 1100 YES
2040 Build 1970 1675 YES 1000 YES
77
S Eads Street/Army Navy Drive
The geometric constraints of the Design Concept combined with heavy traffic demands at the S Eads
Street/Army Navy Drive intersection (during both a.m. and p.m. peak hours) are anticipated to produce
extensive queuing on all approaches. This queue spillback has been observed along Army Navy Drive in
both directions limiting throughput of neighboring intersections.
The eastbound approach currently produces queue spillback during existing conditions, a circumstance
anticipated to be mitigated in the Design Concept by including a dedicated left-turn lane. However,
other conflicting approach demands (particularly the heavy westbound through), and the need for
protected-only left-turn phasing also limit the ability to effectively process those volumes with single
lanes (493 eastbound left turns during 2020 p.m. peak hour versus 845 westbound thru-right turns).
Table 15 shows the maximum simulated queue results of eastbound left turn movement from no-build
and build models. The eastbound left-turn lane was modeled at the greatest possible length
(approximately 420-feet long) in the build models, which still cannot accommodate the heavy left-turn
demand. Queue spillback was observed in the build models during the peak periods and in the no-build
models during only the p.m. peak period.
Table 15 Maximum simulated Queues at Eastbound Eads Street/Army Navy Drive Intersection
EB Eads Approach Storage (ft) 95th-Percentile Queue
AM Adequate Storage? PM Adequate Storage?
2020 No-Build 540 700 NO 700 NO
2020 Build 420 300 YES 650 NO
2040 No-Build 540 700 NO 700 NO
2040 Build 420 650 NO 700 NO
It is anticipated that mitigating the queue spillback issue cannot be resolved through signal
timing/phasing changes, but requires additional lane capacity to process the volume demand.
78
SECTION 7
Summary of Findings
80
81
SUMMARY OF FINDINGS
While the purpose of the Design Concept is to promote and accommodate active transportation
(pedestrians and bicyclists) and transit use along Army Navy Drive, this study focuses on the automobile
and transit performance associated with the proposed improvements. Given the right-of-way
constraints along the Army Navy Drive corridor, trade-offs are inherent when accommodating multi-
modal needs. For corridors that undergo complete street improvements to provide pedestrian, bicycle,
and transit facilities, oftentimes traffic operations for vehicles degrade due to the reduction of travel
lanes and intersection capacity. The purpose of this study is to identify the level of impact to traffic
operations along the corridor and identify mitigation strategies to reduce impacts while
accommodating safety and the performance needs of non-auto users.
The operational analysis of existing, future no-build, and build traffic conditions identified several
intersections and movements that experience long queues, traffic congestion, and turning movements
that operate at Level of Service (LOS) E or F, which causes motorists at those movements to experience
high delays. Table 16 summarizes which intersections are anticipated to experience this by scenario.
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Table 16 Intersections with Peak Hour LOS E or Worse by Scenario
Peak Hour Intersection 2015 Existing 2020 No-Build 2020 Build 2040 No-Build 2040 Build
AM
Army Navy Drive & Joyce
Army Navy & Pentagon Mall E E
Army Navy & Hayes E E F
Army Navy & Fern
Army Navy & Eads E E E
Army Navy & 12th F* F E E F
PM
Army Navy Drive & Joyce
Army Navy & Pentagon Mall
Army Navy & Hayes E
Army Navy & Fern E E
Army Navy & Eads F F F F
Army Navy & 12th * F F F F
*Indicates unsignalized intersection configuration
While individual intersection operations do not reflect the complete picture of how the system
performs under different Design Concepts, it helps identify the location of bottlenecks and “hot spots”
to warrant more-detailed investigation.
S Joyce Street/Army Navy Drive
Positioned on the western end of the corridor, the intersection at S Joyce Street/Army Navy Drive is
anticipated to operate at LOS D or better under all scenarios. Notable findings include:
The eastbound approach experiences higher delays under the build scenarios notably due to
heavy left-turn movements limited by protected-only phasing.
The 2040 build scenario is exacerbated by heavier volume demands on all approaches,
particularly left-turns.
Pentagon Mall Garage/Army Navy Drive
The intersection at Pentagon Mall Garage/Army Navy drive is expected to experience LOS E or worse
under both 2040 no-build and build scenarios during the weekday a.m. peak hour. Notable findings
include:
The westbound left-turn movement into the parking garage experiences the highest delay of all
movements at the intersection in all scenarios.
Reconfiguration of the parking garage exit in the build scenario is anticipated to accommodate
traffic demands without undue delay and queuing.
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S Hayes Street/Army Navy Drive
The intersection of S Hayes Street/Army Navy Drive is among the most critical along the corridor. It is
projected to operate at LOS E, or worse, under both build scenarios and 2040 no-build conditions
during the weekday a.m. peak hour. In all scenarios, the intersection’s connection to Interstate-395 (I-
395) and Washington Boulevard required queuing to be managed on the southbound approach to
prevent spillback onto the freeways. Notable findings include:
Northbound left turns experience high delays under both build and no-build conditions.
Southbound lefts experience high delays attributed to high demand.
Dual southbound left turn lanes were analyzed but have limited benefit due to queuing on the
downstream approach.
Results from the Vissim simulation analysis indicate that the maximum queue on the
southbound approach is not anticipated to spillback onto either I-395 or Washington Boulevard
under any future scenario analyzed.
S Fern Street/Army Navy Drive
The S Fern Street/Army Navy Drive intersection is mostly a point between the bottlenecks at S Hayes
Street and S Eads Street. The intersection is anticipated to operate at LOS E, or worse, only during the
2040 scenarios, mostly driven by queue spillback and heavy side street demands. Notable findings
include:
The northbound approach is anticipated to experience high delays in all future scenarios.
Eastbound delays at the intersection are mostly due to queue spillback from the S Eads
Street/Army Navy Drive intersection.
S Eads Street/Army Navy Drive
The intersection at S Eads Street/Army Navy Drive is a bottleneck along the corridor, given it is used to
access northbound I-395 and bus routes destined to the Pentagon. Both no-build and build lane
configurations have notable limitations in facilitating the traffic demand in future scenarios. Notable
findings include:
Eastbound left-turn queues consistently spill back through S Fern Street and S Hayes Street,
limiting throughput of the western intersections.
The heavy eastbound left-turn movement demand conflicts with a heavy westbound through
movement demand, thus competing for green time and causing delays to automobiles and
buses.
Northbound S Eads Street is constrained by a single approach lane given the relatively short
turn pockets.
The I-395 HOT lanes and associated improvements are expected to improve the operations at S
Eads Street and may relieve some of the anticipated congestion.
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Army Navy Drive/12th Street S
The intersection is currently unsignalized. Based on Arlington County plans, the intersection is planned
to be signalized in conjunction with the neighboring Clark Street/12th Street S intersection in the future.
The signalization will include the addition of median-running transit lanes as part of the 12th Street S
transit facility project. These improvements were assumed in the all future build and no-build
conditions. Notable findings from the analysis of this intersection include:
If unsignalized, the southbound movements are projected to experience significant queuing and
delay.
If signalized based on current plans, the following operational inefficiencies are anticipated: o Long clearance intervals due to the separation of the two intersections (12th Street and
Clark Street); o Limited flexibility to reallocate green time across phases due to the two-intersection
phasing. o The intersection (in conjunction with 12th Street S/Clark Street) has heavy turning
volumes compared to through volumes.
SCENARIO FINDINGS
Existing Conditions
General findings from the simulation analysis of existing conditions include:
Simulation results match with field observations of queues and driver behavior.
Simulation results at the intersection level are comparable to the Synchro analysis results.
Future No-Build Conditions Findings
General findings from the simulation analysis of no-build conditions include:
Significant congestion was observed in both future years during the weekday a.m. and p.m.
peak hours, notably at S Hayes Street, S Fern Street, S Eads Street and 12th Street
intersections.
Queue storage on the southbound S Hayes Street approach (I-395 ramp) is accommodated
through 2040 for both a.m. and p.m. peak hours.
The observed bottleneck is the eastbound approach at S Eads Street/Army Navy Drive. The
current eastbound lane configuration consists of a left-through and through-right layout,
which negatively impacts the progression of left-turn and through movements. The future-
year simulation analysis shows that demand is heavy on all legs with the predominant
conflicting movements being the eastbound left-turn movement and westbound through
movement. With heavy volumes destined to northbound I-395 and the limitation of a single
receiving lane, congestion is not expected to be alleviated by signal timing and phasing
improvements.
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Future Build Conditions Findings
General findings from the simulation analysis of build conditions include:
Significant congestion was observed in both future years during both weekday a.m. and
p.m. peak hours, notably at S Hayes Street, S Fern Street, S Eads Street, and 12th Street S
intersections.
Queue storage on the southbound S Hayes Street approach (I-395 ramp) accommodates the
back of queue through 2040 for both weekday a.m. and p.m. peak hours.
Both build and no-build conditions show a major network bottleneck at the S Eads
Street/Army Navy Drive intersection.
o Similar to the no-build analysis the future-year simulation analysis indicates heavy
demand on all legs; the main conflicting movements are the eastbound left-turn
movement and westbound through movement. With heavy volumes destined to the
northbound direction towards I-395 and the limitation of a single receiving lane,
congestion is not expected to be alleviated by signal timing and phasing improvements.
o Queue storage for the eastbound left-turn is recommended to be extended as far as
possible, but block spacing remains a limiting factor. Even with maximum storage, left-
turn queue spillback is anticipated.
The overall Design Concept reduces vehicular capacity along Army Navy Drive by
reallocating right-of-way to non-auto users. However, as summarized in Table 16, all study
intersections anticipated to operate at LOS E, or worse, in 2040 will do so under both build
and no-build conditions, with the only exception being the intersection of Army Navy
Drive/S Hayes Street.
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RECOMMENDATIONS
The following section details the recommendations for the Design Concept, both geometric design and
signal operations, based on the traffic analysis completed.
GEOMETRIC RECOMMENDATIONS
The following section summarizes the geometric recommendations, shown graphically in Figures 45
through 50.
1. Joyce Street/Army Navy Drive
a. Northbound approach should be designed with a bike box configuration to
accommodate WB cyclists exiting the bicycle facility and continuing WB on Army Navy
Drive or turning right onto Joyce Street.
b. Westbound approach should be able to accommodate U-turns to provide access to the
Harris Teeter parking garage due to closing the existing median left-turn lane.
c. Southbound approach requires maintaining a left-turn lane with minimum storage
consistent with existing configuration.
Figure 42 – S Joyce Street/Army Navy Drive Recommendations Summary
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2. Parking Garage/Army Navy Drive
a. The northbound approach should be modified to a dedicated left-turn, dedicated
through, and dedicated right-turn lane configuration.
b. Pentagon Transit Center Considerations - Resolution with the ultimate design of the
Transit Center by the Pentagon must consider the west crosswalk as the latest designs
currently do not depict this pedestrian crossing. Include revised southbound approach
to shared left-through lane and dedicated right turn lane.
c. The westbound left-turn lane requires additional storage.
i. The current left-turn lane length shown in the Design Concept between Parking
Garage (on westbound Army Navy Drive) and Hayes Street (on eastbound Army
Navy Drive) should accommodate anticipated queues.
ii. Storage length of the westbound left-turn lane is as follows:
1. WB Army Navy Drive @ Parking Garage = 130-ft; 75-ft taper
Figure 43 – Pentagon Mall Garage/Army Navy Drive Recommendations Summary
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3. Hayes Street/Army Navy Drive
a. The near-side bus stop along eastbound Army Navy Drive requires pedestrian
accommodations across the two-way bike lanes; consider similar treatment to mid-
block stop between Joyce Street and Parking Garage.
b. The northbound bike lane should be aligned along the curb rather than between the
through and right-turn lanes to prevent right-turning cyclists from conflicting with right-
turning vehicles. The model assumed that northbound left-turning cyclists would merge
into the vehicle lanes, but there are alternatives for accommodating left-turning cyclists.
A two-stage left-turn bike box could be installed or a bike signal/phase could be
considered. Although, an exclusive bike phase would result in a longer cycle length.
c. The southbound right-turn lane should have advanced signage of pedestrian crossing for
the channelized lane to encourage motorists to reduce speeds.
d. Dual southbound left-turn lanes have been considered but are not recommended. The
eastbound downstream through capacity limits any benefit of dual left-turn lanes.
e. Storage length of the left-turns lane are as follows:
iii. EB Army Navy Drive @ Hayes Street = 220-ft; 60-ft taper
iv. WB Army Navy Drive @ Hayes Street = 125-ft; 60-ft taper
Figure 44 – S Hayes Street/Army Navy Drive Recommendations Summary
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4. Fern Street/Army Navy Drive
a. Consider access management alternatives, such as limiting ingress, regarding the
driveway on far-side of eastbound Army Navy Drive at Fern Street; potential right-out
only configuration to reduce conflicts with pedestrians and cyclists.
b. The northbound approach should be reconfigured as a designated left-turn lane,
through lane, and designated right-turn lane.
c. Storage length of the left-turns lane are as follows:
iii. EB Army Navy Drive @ Fern Street = 150-ft; 60-ft taper
iv. WB Army Navy Drive @ Fern Street = 50-ft; 60-ft taper
Figure 45 – S Fern Street/Army Navy Drive Recommendations Summary
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5. Eads Street/Army Navy Drive
a. The eastbound left-turn lane requires the maximum storage possible within the block
due to heavy bus movements and traffic demands.
b. Consider revisions to the westbound approach to reduce conflict points; the design
should consider:
i. Restricting westbound traffic movements from US 110 (Jefferson Davis Highway)
from turning left onto Eads Street.
ii. Providing better accommodations at the existing pedestrian crossing on the US-
110 off-ramp. The County will conduct a marked crosswalk study in order to
determine what treatments are warranted for this location. The study will be
submitted to VDOT in a separate memorandum.
c. The northbound approach would benefit from elongating the two-lane cross-section
south to 11th Street S for additional capacity.
d. Storage length of the left-turns lane are as follows:
i. EB Army Navy Drive @ Eads Street = 420-ft; 60-ft taper
ii. WB Army Navy Drive @ Eads Street = 135-ft; 60-ft taper
Figure 46 – S Eads Street/Army Navy Drive Recommendations Summary
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6. Army Navy Drive /12th Street S
a. Transit-only lanes between Army Navy Drive and 12th Street S should be converted to
general traffic lanes to improve traffic throughput.
i. Transit-only lanes between both intersections do not reduce bus delay with
recommended signal timing/phasing, which allows buses to use the segment
exclusively.
b. Prohibit westbound left turns due to sight distance concerns. Must provide westbound
U-turn movement at S Eads Street/12th Street S intersection to access garage.
Figure 47 – Army Navy Drive/12th Street S Recommendations Summary
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SIGNAL-RELATED RECOMMENDATIONS
A 130-second cycle length is recommended for 2020 weekday a.m. peak hour build scenario.
A 140-second cycle length is recommended for 2020 weekday a.m. peak hour and both 2040
weekday a.m. and p.m. peak hour scenarios.
Implement protected-only left-turn phasing along Army Navy Drive to reduce conflicts between
westbound left-turning vehicles, pedestrians, and bicyclists.
Eastbound/westbound bicycle movements along the bike facility will run concurrently with the
eastbound through phase.
Ensure all pedestrian intervals meet MUTCD recommended standards.
The Army Navy Drive/12th Street S intersection meets traffic signal warrants under Year 2020
and Year 2040 volume conditions and should be signalized. It is recommended that this
intersection run on the same controller as Clark Street/12th Street S and will be constructed as
part of the Crystal City Potomac Yard (CCPY) Transitway Extension project.
All analyzed signal timing parameters found in Appendix I.
SECTION 8
Recommendations
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REFERENCES
1. VDOT Functional Classification map: http://www.virginiadot.org/projects/fxn_class/maps.asp
2. Virginia Department of Transportation. Traffic Operations and Safety Analysis Manual. Version
1.0. November 2015.
3. Gorove/Slade. Traffic Impact Study and Transportation Demand Management – PenPlace Site.
Arlington County, Virginia. May 3, 2012.
4. Gorove/Slade. Traffic Impact Study and Transportation Management Plan – 400 Army Navy
Drive. Arlington County, Virginia. June 11, 2013.
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