Traffic Bottlenecks: Identification and Solutions

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FOREWORD

The far-reaching detrimental impacts on mobility, the environment, and the economy caused by recurring congestion are well known. This report adds to the vast amount of research on congestion mitigation by developing a new approach for ranking traffic bottlenecks, introducing a new playbook of 70 bottleneck mitigation strategies, conducting a benefit-cost analysis of 5 low-cost bottleneck mitigation strategies, and introducing 3 new bottleneck mitigation strategies. This report describes a data-driven congestion and bottleneck identification software tool and details low-cost operations-focused solutions, including dynamic lane use, contraflow or reversible lane use, hard shoulder lane use, lane width reduction, and modest extension of auxiliary lanes. This report will be of interest to practitioners involved in the transportation operations discipline.

Brian Cronin
Director, Office of Operations
Research and Development

Technical Report Documentation Page

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

EXECUTIVE SUMMARY

CHAPTER 1. INTRODUCTION

CHAPTER 2. BOTTLENECK IDENTIFICATION

• Problem Statement
• Definition of Congestion
• Classification of Bottlenecks
• Spatio-Temporal Matrix (STM)
• Conventional Methods
• Data-Driven Methods
• Bottleneck Rankings
• ARM
• California Method—Vehicle-Hours of Delay
• Bottleneck Intensity Index (BII)
• Signalized Arterials
• Summary
• CBI Tool Use Tips
• CBI Tool Distribution

CHAPTER 3. BOTTLENECK MITIGATION CONCEPTS

• Definition of Bottlenecks
• Attributions of Bottlenecks
• Bottleneck Identification Framework

CHAPTER 4. COST-EFFECTIVE SOLUTIONS FOR BOTTLENECK MITIGATION

• Alternative Intersections and Interchanges
• DLG
  • DLG Screening Criteria
  • Data Collection and Analysis
  • Case Studies
  • Implementation Example
  • B/C Analysis
  • Design Guidance for Safe and Efficient Implementation of DLG
  • Summary
• Dynamic Junction Control (DJC)
  • Research Background
  • Road Geometries Selection
  • Model Calibration
  • Performance of DMC for Freeway-to-Freeway Merges
  • Performance of DMC for On-Ramp to Freeway Merges.
  • B/C Analysis
  • Design Guidance for Safe and Efficient Implementation of DMC
  • Summary
• Extending Acceleration Lane Lengths
  • B/C Analysis
• HSR
  • B/C Analysis
• Reducing Existing Lane and Shoulder Widths to Add New Lanes
  • B/C Analysis
• Summary
• Recommendations for Future Research

CHAPTER 5. INNOVATIVE SOLUTIONS FOR BOTTLENECK MITIGATION

• Dynamic HSR
  • Incident Types
  • Simulation Experiments
  • Experimental Results
  • Design Guidance for Safe and Efficient Implementation of Dynamic HSR
• DRLT Lanes
  • Maryland Case Study
  • Virginia Case Study
  • Conclusions for Virginia and Maryland Case Studies
  • Design Guidance for Safe and Efficient Implementation of DRLT Lanes
• CLT Pockets
  • Maryland Case Study
  • Sensitivity Analysis
  • Design Guidance for Safe and Efficient Implementation of CLT Pockets
  • Implementations in China

CHAPTER 6. CONCLUSIONS

APPENDIX. PLAYBOOK OF BOTTLENECK SOLUTIONS

REFERENCES

LIST OF FIGURES

Figure 1. Graph. Traffic congestion causes from 2004
Figure 2. Graph. Vehicle delay versus degree of traffic congestion
Figure 3. Screenshot. CBI software tool
Figure 4. Screenshot. Conventional lanes at a signalized diamond interchange
Figure 5. Screenshot. DRLT lanes at a signalized diamond interchange
Figure 6. Graph. Survey results for defining congestion
Figure 7. Flowchart. Generation of STMs via measurements or models
Figure 8. Graph. Reliability analysis box
Figure 9. Graph. Concept of bottleneck intensity (percentage of analysis box that is congested)
Figure 10. Screenshot. Congestion identification heat map from the RITIS Web site
Figure 11. Screenshot. Bottleneck rankings from the RITIS Web site
Figure 12. Equation. Impact factors for bottleneck rankings
Figure 13. Graph. STM used to compute bottleneck intensity
Figure 14. Graph. ARM based on bottleneck intensity
Figure 15. Graph. ARM illustrating relatively good bottleneck reliability
Figure 16. Graph. ARM illustrating relatively poor bottleneck reliability
Figure 17. Screenshot. CBI tool with ARM (upper right) and speed drop (lower right)
Figure 18. Equation. Delay per vehicle on each traffic message channel (TMC)
Figure 19. Equation. Vehicle-hours of delay on each TMC
Figure 20. Screenshot. Newer CBI software tool featuring vehicle-hours of delay
Figure 21. Graph. ARM illustrating relatively good bottleneck reliability based on vehicle-hours of delay
Figure 22. Graph. ARM illustrating relatively poor bottleneck reliability based on vehicle-hours of delay
Figure 23. Graph. Comparison of bottleneck locations based on BII—I-695 example
Figure 24. Graph. Comparison of bottleneck locations based on BII—I-495 example
Figure 25. Graph. Comparison of bottleneck locations based on BII—I-895 example
Figure 26. Graph. STM before wavelet filtering
Figure 27. Graph. STM after wavelet filtering
Figure 28. Screenshot. Example of missing data in the CBI tool
Figure 29. Flowchart. Framework to identify causes of bottlenecks
Figure 30. Illustration. Example of LT congestion prior to DLG
Figure 31. Illustration. Example of LT congestion after DLG
Figure 32. Equation. Minimum acceptable demand volumes for DLG
Figure 33. Equation. Minimum change in turn volumes for DLG
Figure 34. Equation. Minimum change in TH volumes for DLG
Figure 35. Equation. Different congestion in adjacent movements for DLG
Figure 36. Equation. Sufficient turn movement congestion for DLG
Figure 37. Equation. Minimal TH movement congestion for DLG
Figure 38. Equation. Severe turn movement congestion for DLG
Figure 39. Illustration. Morning peak configuration for case study 1
Figure 40. Illustration. Afternoon peak configuration for case study 1
Figure 41. Illustration. Lane assignment before DLG for case study 1
Figure 42. Illustration. Lane assignment after DLG for case study 1
Figure 43. Illustration. Traffic demand for case study 2
Figure 44. Equation. Monetary savings for each vehicle-hour of delay reduction
Figure 45. Equation. Total hourly time savings for the DLG example
Figure 46. Equation. Annual cost savings for the DLG example
Figure 47. Photo. Upstream DLG signage in Maryland
Figure 48. Illustration. DMC
Figure 49. Illustration. Merging of multiple two-lane freeways (closure on route B)
Figure 50. Illustration. Merging of multiple two-lane freeways (closure on route A)
Figure 51. Illustration. Merging of three- and two-lane freeways (closure on route B)
Figure 52. Illustration. Merging of three- and two-lane freeways (closure on route A)
Figure 53. Illustration. Merging of one-lane ramp and two-lane mainline (closure on mainline)
Figure 54. Illustration. Merging of one-lane ramp and three-lane mainline (closure on mainline)
Figure 55. Illustration. Merging of one-lane ramp and four-lane mainline (closure on mainline)
Figure 56. Equation. Simulated values and mean values over all simulation replications
Figure 57. Equation. RRMSE
Figure 58. Equation. FHWA GEH criteria
Figure 59. Equation. Total hourly time savings for the DMC example
Figure 60. Equation. Total daily time savings for the DMC example
Figure 61. Equation. Annual cost savings for the DMC example
Figure 62. Illustration. Automated gate option for DMC
Figure 63. Photo. Real-world image of an automated gate
Figure 64. Illustration. Acceleration lane length schematic (three-lane configuration)
Figure 65. Illustration. Acceleration lane geometry
Figure 66. Graph. Total delay for three mainline lanes and 40-mi/h ramp speed
Figure 67. Graph. Total delay for three mainline lanes and 30-mi/h ramp speed
Figure 68. Graph. Total delay for four mainline lanes and 40-mi/h ramp speed
Figure 69. Graph. Total delay for four mainline lanes and 30-mi/h ramp speed
Figure 70. Equation. Total daily time savings for extended acceleration lanes
Figure 71. Equation. Annual cost savings for extended acceleration lanes
Figure 72. Illustration. HSR strategy schematic
Figure 73. Illustration. Base year analysis of reducing lane widths to add new lanes
Figure 74. Illustration. Equivalent freeway scenario with five mainline lanes
Figure 75. Graph. Speed reduction as a function of lane width
Figure 76. Illustration. Dynamic HSR for incident response
Figure 77. Equation. Free-flow speed from lane width and lateral clearance
Figure 78. Illustration. Typical signalized diamond interchange with back-to-back LT lanes
Figure 79. Map. Selected signalized diamond interchange case study
Figure 80. Illustration. Interchange traffic patterns
Figure 81. Screenshot. Georgetown Pike interchange with conventional lanes
Figure 82. Screenshot. Georgetown Pike interchange with DRLT lanes
Figure 83. Illustration. DRLT design for a four-lane road with a single LT lane
Figure 84. Illustration. DRLT design for a four-lane road with dual LT lanes
Figure 85. Illustration. DRLT design for a six-lane road with dual LT lanes
Figure 86. Illustration. Proposed single-lane DRLT signalization during peak-period green phases
Figure 87. Illustration. Proposed single-lane DRLT signalization during off-peak-period green phases
Figure 88. Illustration. Proposed single-lane DRLT signalization during red phases for all periods
Figure 89. Illustration. DMSs for dual DRLT lanes during peak and off-peak periods
Figure 90. Illustration. Signal phasing and ring structure for proposed DRLT diamond interchanges
Figure 91. Equation. Calculation of DRLT signal TCL
Figure 92. Photo. Upstream advance warning sign for DRLT
Figure 93. Map. Example of no re-entry signage
Figure 94. Illustration. CLT intersection geometry
Figure 95. Illustration. Turn movement volumes at Tuckerman Lane and Rockville Pike in Maryland
Figure 96. Graph. Delay reductions due to CLT at various LT demand levels
Figure 97. Graph. Throughput increases due to CLT at various LT demand levels
Figure 98. Illustration. CLT pocket configuration
Figure 99. Illustration. Expected CLT lane utilization under low LT demand
Figure 100. Illustration. Expected CLT lane utilization under medium LT demand
Figure 101. Illustration. Expected CLT lane utilization under high LT demand
Figure 102. Equation. 95th percentile queue length
Figure 103. Equation. 95th percentile back-of-queue factor
Figure 104. Illustration. Side-swipe risk between CLTs and adjacent RTs
Figure 105. Illustration. Presignal at CLT pocket entrance
Figure 106. Illustration. Proposed CLT signalization during peak period
Figure 107. Illustration. Proposed CLT signalization during off-peak period
Figure 108. Illustration. CLT pocket signalization
Figure 109. Illustration. CLT intersection geometry
Figure 110. Equation. Calculation of CLT signal TCL for clearing the turn pocket
Figure 111. Equation. Calculation of CLT signal TCL for ensuring safe pocket entry
Figure 112. Equation. Truncated green time based on vehicle clearance
Figure 113. Equation. Truncated green time based on original green time
Figure 114. Map. CLT implementations in China
Figure 115. Photo. CLT intersection in China before the presignal has turned green
Figure 116. Photo. CLT intersection in China after the presignal has turned green but before the main signal has turned green
Figure 117. Photo. CLT intersection in China after the main signal has turned green

LIST OF TABLES

Table 1. Selected FHWA bottleneck relief sources
Table 2. New concepts affecting bottleneck rankings
Table 3. Traffic bottleneck attributes
Table 4. Number of candidates selected in each network by four criteria
Table 5. Analysis of the flagged candidates
Table 6. DLG benefits for case study 1
Table 7. DLG benefits of case study 2
Table 8. WB turning movement counts at the Shady Grove intersection
Table 9. DMS capital and operating costs
Table 10. Freeway-to-freeway merge scenarios
Table 11. Freeway on-ramp merge scenarios for DMC
Table 12. Calibrated driving behavior parameters
Table 13. AVD saving by the DMC strategy (s)
Table 14. AVD savings by the DMC strategy (s)
Table 15. AVD savings by the DMC strategy (mainline lane closure) (s)
Table 16. AVD saving by the DMC strategy for two-lane by two-lane ramp closure (s)
Table 17. AVD saving by the DMC strategy (s)
Table 18. AVD savings by the DMC strategy (s)
Table 19. AVD (s) savings by the DMC strategy (four-lane freeway
Table 20. Geometric configurations for testing acceleration lane lengths
Table 21. Volume demands for testing acceleration lane lengths (three-lane configuration)
Table 22. Volume demands for testing acceleration lane lengths (four-lane configuration)
Table 23. Estimated annual cost savings for increased acceleration lane length
Table 24. HSR summary results
Table 25. HSR delay reductions
Table 26. Possible cost savings under various scenarios of HSR
Table 27. Summary results of reducing lane widths to add new lanes
Table 28. Additional results from reducing lane widths to add new lanes
Table 29. Case study simulation results for DRLT lanes
Table 30. Case study simulation results for CLT pockets
Table 31. Sensitivity analysis experimental design for CLT

LIST OF ABBREVIATIONS