Enhancing Safety and Operations at Complex Interchanges With Improved Signing, Markings, and Integrated Geometry

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FOREWORD

The National Highway System has experienced rapid growth in demand that has far outpaced the increase in new capacity. Roadway designers are turning toward additional lanes, preferential lanes and ramps, and multilane exits in their interchange designs to address the continued mobility demands. While these mobility and capacity enhancements address the challenge of increased demand, they also complicate the design and operation of interchanges.

Drivers approaching these complex interchanges are required to perform several navigation tasks that are often short in both distance and time. The purpose of this study was to develop recommendations for signing, delineation, and geometric design that will reduce workloads at critical points approaching complex interchanges. In doing so, this project identified many attributes that contribute to complexity; evaluated multiple interchanges across the United States for their design, signing, and marking practices; conducted a series of driving simulator studies; and observed and analyzed video investigating real-world driving behaviors at complex interchanges.

Each key finding and recommendation is provided in the report, along with examples that explain the involved principles and suggested guidelines for implementation. This report should be useful to transportation professionals, State transportation departments, and researchers interested in developing complex interchange designs that consider driver behavior more effectively.

Monique R. Evans, P.E., CPM
Director, Office of Safety
Research and Development

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

Table of Contents

• Executive Summary
  
  
• Chapter 1. Introduction
  • Using This Report
  • Approach and Outcomes
  • Basis of Recommendations
  • Preparation for the Final Report
    
    
• Chapter 2. Summary of Contemporary Research Efforts
  • Approach
  • Driver Expectations of Interchanges
    • Driver Expectations
    • Perceptual Factors
  • Identifying Complex Situations
  • Existing Design Guidance
    • Interchange Geometry
    • Traffic Signing and Pavement Markings
  • Interchange Design Practice
    • Interchange Layout
    • Interchange Modification Strategies
    • Interchange Signing Practices
    • Interchange Pavement Marking Practices
    • Barriers to Best Practice
  • Summary
    
    
• Chapter 3. Attributes Contributing to Complexity
  • Development of Attribute List
    • Group 1000—Impacts and Outcomes
    • Group 2000—User Characteristics
    • Group 3000—System Design
    • Group 4000—Roadway Geometric Design
    • Group 5000—TCD
    • Group 6000—Management and Operations
    • Group 9000—Institutional Factors
  • Selection of Topics
    
    
• Chapter 4. Site Evaluation and Selection
  • Selection of Participating States
  • Partnership Agreements And Memoranda
    • Host State Documentation
  • Site Selection Process
    • Selection Criteria
    • Candidate Interchange Sites
  • Study Efforts
    
    
• Chapter 5. Practices Evaluation
  • Defining Inconsistency
    • Implementing Consistency
  • Inconsistency Examples
    • Option Lane Signing
  • Observed Practices
    • Geometric Design and Traffic Control Devices
    • Pavement Markings and Delineation
    • RRPMs
  • Institutional Observations
    
    
• Chapter 6. Simulator Study
  • Objective
  • Research Questions
  • Interchange Design and Signing Approaches
    • Layout A
    • Layout L
    • Layout C
    • Layout E
  • Research Design
    • Independent and Dependent Variables
    • Controlling for Order Effects
    • Detecting Differences in Driving Performance
  • Method
    • Participants
    • Apparatus
    • Materials
    • Stimuli
    • Procedures
  • Data Reduction and Analysis Approach
  • Results
    • Accuracy
    • ULCs
    • LSD
  • Discussion
    
    
• Chapter 7. Field Study
  • Study Design
  • Data Collection Process and Methods
    • Site Visit Preparation
    • Data Collection Methods
    • Data Reduction
    • Data Analysis
  • Site Descriptions and Results
    • Site 11—Orlando, FL
    • Site 27—Atlanta, GA
    • Site 31—Minneapolis, MN
    • Site 43—Olympia, WA
  • Field Study Findings
    
    
• Chapter 8. Key Findings
  • Practitioner Input
  • Literature and Technical Policy Review
  • Practices Evaluation
  • Simulator Study
    • Layout A
    • Layout E
  • Field Study
  • Summary of Key Findings
    
    
• Chapter 9. Proposed Treatments
  • Introduction
  • Treatment 1—Ramp Terminal Arrangements and Design
    • Introduction
    • Design Guidelines
    • Research Findings
    • Recommendations
    • Implementation
  • Treatment 2—Guide Signing: Sign Legend Arrangement and Panel Configurations
    • Introduction
    • Design Guidelines
    • Research Findings
    • Recommendations
    • Implementation
  • Treatment 3—Guide Signing: Sign Placement and Use of Arrows and Distances
    • Introduction
    • Design Guidelines
    • Research Findings
    • Recommendations
    • Implementation
  • Treatment 4—Delineation for Exiting Lanes and Special Use Lanes
    • Introduction
    • Design Guidelines
    • Research Findings
    • Recommendations
    • Implementation
  • Treatment 5—Lane-Reduction Methods, Signing, and Delineation
    • Introduction
    • Design Guidelines
    • Research Findings
    • Recommendations
    • Implementation
  • Treatment 6—TCDs Education and Design Review Workshops
    • Introduction
    • Design Guidelines
    • Recommendations
    • Implementation
      
      
• Appendix A. Candidate Site Information Sheets (Supplement to Chapter 4)
  • Introduction
  • Location 1: I-880 at SR 237 in Milpitas, CA
  • Location 2: I-110 at I-105 in Los Angeles, CA
  • Location 3: I-5 at California Routes 22 and 57 Freeways in Santa Ana, CA
  • Location 4: I-75 at I-285 Northwest Junction in Atlanta, GA
  • Location 5: I-75 at I-85 North Junction in Atlanta, GA
  • Location 6: I-85 at I-285 Southwest Junction in College Park, GA
  • Location 7: I-85 at Georgia Route 400 Toll Road in Atlanta, GA
  • Location 8: I-85 at I-285 Northeast Junction in Atlanta, GA
  • Location 9: I-35W at Minnesota Crosstown Freeway/TH 62 in Minneapolis, MN
  • Location 10: I-35W at Highways 36 and 280 in Minneapolis, MN
  • Location 11: I-394 at Highway 100 in Golden Valley, MN
  • Location 12: I-5 at I-90 and Seattle Downtown Exits in Seattle, WA
  • Location 13: I-5 at I-405 and Route 518 in Tukwila, WA
    
    
• Appendix B. Diagrams of Layouts With Signing Alternatives (Supplement to Chapter 6)
  • Introduction
    
    
• Appendix C. Instructions to Participants (Supplement to Chapter 6)
  • INSTRUCTIONS
    • Practice Drive
    • Experimental Drives
      
      
• Appendix D. Participant Questionnaire (Supplement to Chapter 6)
  
  
• References

List of Figures

• Figure 1. Graphic. Project process for developing and organizing information
• Figure 2. Photo. Satellite imagery of northbound Interstate 5 (I-5) C/D roadway north of I-90 with multiple successive lane-reduction arrows
• Figure 3. Photo. Washington State Route (SR) 520 westbound near 92nd Avenue northeast
• Figure 4. Graphic. Hierarchal organization of attribute 4241
• Figure 5. Graphic. AASHTO Green Book excerpt of partial cloverleaf design A, depiction E from figure 10-1
• Figure 6. Photo. Multilane entrance ramp with tapered design, I-80 at I-94 eastbound, Lansing, IL
• Figure 7. Photo. I-4 distributor roadway upstream of US 192 interchange in Kissimmee, FL, showing left exit from the distributor roadway
• Figure 8. Photo. Ramp from I-35E southbound to I-94 and US 52, Saint Paul, MN
• Figure 9. Photo. US 175 interchange with I-20 in Dallas, TX, with upstream exit carrying left-turning traffic to northeast-bound I-20
• Figure 10. Graphic. Configurations of exiting lanes
• Figure 11. Photo. Example of exit-direction signs based on MUTCD figure 2E-12
• Figure 12. Graphics. Two examples of guide signs for option lane signing
• Figure 13. Photo. Example of exit-direction signs
• Figure 14. Photo. Escape lane signing that does not adhere to the consistency principle because the continuing lane is signed as an exit-only lane
• Figure 15. Photos. Exit gore signs
• Figure 16. Photo. New installation of blended arrow guide sign in North Carolina
• Figure 17. Graphics. Two examples of inconsistent arrow design
• Figure 18. Graphic. Arrows for use on guide signs (MUTCD 2009, figure 2D-2)
• Figure 19. Graphic. Configurations of exiting and entering lanes
• Figure 20. Photo. Left-hand acceleration lane terminating in a lane-reduction taper
• Figure 21. Photo. Overhead view of entering ramp (lower right of image) with asymmetrical widening to the left in a left-hand horizontal curve
• Figure 22. Photo. Location of left edgeline in an asymmetrical widening over and beyond a crest vertical curve
• Figure 23. Graphic. Excerpt from WSDOT Standard Plan M20.50-02
• Figure 24. Graphic. Interchange layouts considered in this study
• Figure 25. Graphic. Layout E decision points
• Figure 26. Photo. MHFL
• Figure 27. Graphic. Overhead sign that directed participants to a starting lane using the asterisk symbol location in one of four lanes
• Figure 28. Graphics. Participant accuracy for each combination of interchange layout and signing alternative
• Figure 29. Graphic. Histograms of ULCs for each combination of interchange layout and signing alternative
• Figure 30. Graphics. Mean and 95-percent (familywise) confidence intervals for ULCs associated with each signing alternative within interchange layout
• Figure 31. Graphic. Survival analysis with 95-percent confidence intervals: layout A, DP1
• Figure 32. Graphic. Survival analysis with 95-percent confidence intervals: layout A, DP2
• Figure 33. Graphic. Survival analysis with 95-percent confidence intervals: layout C, DP1
• Figure 34. Graphic. Survival analysis with 95-percent confidence intervals: layout C, DP2
• Figure 35. Graphic. Survival analysis with 95-percent confidence intervals: layout E, DP1
• Figure 36. Graphic. Survival analysis with 95-percent confidence intervals: layout E, DP2
• Figure 37. Graphic. Survival analysis with 95-percent confidence intervals: layout L, DP1
• Figure 38. Graphic. Survival analysis with 95-percent confidence intervals: layout L, DP2
• Figure 39. Graphic. Layout A signing alternative examples
• Figure 40. Graphic. Layout C signing alternative examples
• Figure 41. Graphic. Layout E signing alternative examples
• Figure 42. Graphic. Layout L signing alternative examples
• Figure 43. Graphics. Site 27 data
• Figure 44. Graphic. Example cluster analysis results (site 27)
• Figure 45. Photo. Area map of Orlando, FL, data collection segment
• Figure 46. Photo. Example video still from camera 2 at site 11
• Figure 47. Graphic. Common exiting driver behaviors at site 11, eastbound, exit 64 (n = 24)
• Figure 48. Graphic. Common exiting driver behaviors at site 11, eastbound, exit 65 (n = 6)
• Figure 49. Graphic. Common exiting driver behaviors at site 11, eastbound, exit 67 (n = 10)
• Figure 50. Graphic. Common exiting driver behaviors at site 11, westbound, exit 6 (n = 26)
• Figure 51. Graphic. Common exiting driver behaviors at site 11, westbound, exit 65 (n = 13)
• Figure 52. Graphic. Common exiting driver behaviors at site 11, westbound, exit 67 (n = 45)
• Figure 53. Photo. Aerial view of the interchange at site 27
• Figure 54. Photo. Example video still from camera 2 at site 27
• Figure 55. Graphic. Common exiting driver behaviors at site 27, exit 51A (n = 202)
• Figure 56. Graphic. Common exiting driver behaviors at site 27, exit 51B (n = 164)
• Figure 57. Graphic. Splits 1 and 2 at site 31-1
• Figure 58. Photo. I-35W southbound approaching split 1, the three-lane ramp to the Minnesota TH 62 exits
• Figure 59. Graphic. Splits 3L and 3R at site 31-1
• Figure 60. Photo. Camera locations at site 31-2 (Minnesota TH 62 approaching I-35W)
• Figure 61. Photo. Camera positions at site 31-3 (I-35W northbound approaching Minnesota TH 62)
• Figure 62. Graphic. Common exiting driver behaviors at site 31-1, exit 11 (n = 33)
• Figure 63. Photo. Aerial view of the interchange at site 43-1
• Figure 64. Photo. Example video still from UAV at site 43-1
• Figure 65. Photo. Aerial view of the interchange at site 43-2
• Figure 66. Photo. Example video still from UAV at site 43-2
• Figure 67. Photo. Aerial view of the interchange at site 43-3
• Figure 68. Photo. Example video still from UAV at site 43-3
• Figure 69. Graphic. Common exiting driver behaviors at site 43-1, exit 105 (n = 97)
• Figure 70. Graphic. Common exiting driver behaviors at site 43-2, exit 104 (n = 141)
• Figure 71. Graphic. Common exiting driver behaviors at site 43-3, exit 111 (n = 84)
• Figure 72. Photo. Gore area markings on a freeway in South Carolina
• Figure 73. Graphics. Advance guide sign for left exit with “LEFT” inset panels
• Figure 74. Graphic. Sample size class selection table
• Figure 75. Graphic. Excerpt from sample legend and element size table
• Figure 76. Graphics. Option lane signing using the discrete arrow method with a null-terminated two-headed arrow in place of down arrow over option lane
• Figure 77. Photo. Use of multiple signs approaching a single departure point
• Figure 78. Photo. Use of a tapered lane addition to enter the general-purpose lanes of a freeway from the managed lanes
• Figure 79. Photo. Use of misleading signing and parallel lanes and lane changes to access the general-purpose lanes of a freeway from the managed lanes
• Figure 80. Photo. The use of a lane addition taper (marked with a broken red line) not delineated with dotted extension lines
• Figure 81. Graphic. Proposed W4-3X sign for multilane entrances
• Figure 82. Graphic. MnDOT-designed W9-2A(L)
• Figure 83. Graphic. Schematic of proposed lane-reduction signing
• Figure 84. Graphic. Comparison of markings for auxiliary exit-only lanes and acceleration lanes
• Figure 85. Photo. Aerial view of location 1
• Figure 86. Photo. Aerial view of location 2
• Figure 87. Photo. Aerial view of location 3
• Figure 88. Photo. Aerial view of location 4
• Figure 89. Photo. Aerial view of location 5
• Figure 90. Photo. Aerial view of location 6
• Figure 91. Photo. Aerial view of location 7
• Figure 92. Photo. Aerial view of location 8
• Figure 93. Photo. Aerial view of location 9
• Figure 94. Photo. Aerial view of location 10
• Figure 95. Photo. Aerial view of location 11
• Figure 96. Photo. Aerial view of location 12
• Figure 97. Photo. Aerial view of location 13

List of Tables

• Table 1. Correlation of project objectives and project tasks
• Table 2. Basis of recommendations with indexing symbols
• Table 3. Previous project deliverables
• Table 4. Key design principles from existing research
• Table 5. Characteristics of complex interchanges as reported by stakeholders
• Table 6. Factors and weights included in complexity rating tool
• Table 7. Category 1100 traits
• Table 8. Category 1200 traits
• Table 9. Category 1300 traits
• Table 10. Category 1400 traits
• Table 11. Category 2100 traits
• Table 12. Category 2200 traits
• Table 13. Category 2300 traits
• Table 14. Category 2400 traits
• Table 15. Category 3100 traits and attributes
• Table 16. Category 3200 traits and attributes
• Table 17. Trait 4110 and 4120 attributes
• Table 18. Trait 4130 and 4140 attributes
• Table 19. Trait 4210 attributes
• Table 20. Trait 4240 attributes
• Table 21. Trait 4250 to 4270 attributes
• Table 22. Category 4300 traits and attributes
• Table 23. Traits 5110 and 5120 attributes
• Table 24. Trait 5130 attributes
• Table 25. Traits 5140 through 5180 attributes
• Table 26. Trait 5190 attributes
• Table 27. Category 5200 traits and attributes
• Table 28. Category 6100 traits and attributes
• Table 29. Category 6200 trait
• Table 30. Category 6300 traits and attributes
• Table 31. Category 6400 traits and attributes
• Table 32. Category 6500 traits and attributes
• Table 33. Category 6600 traits and attributes
• Table 34. Group 9000 categories
• Table 35. List of topics advanced for testing
• Table 36. Participating agency list and characteristics
• Table 37. Final list of candidate sites for evaluation with field study activities
• Table 38. Candidate sites for evaluation without field study activities
• Table 39. List of field study sites with field study effort descriptions
• Table 40. Applications matrix for inconsistency identification
• Table 41. Pavement marking patterns and typical uses
• Table 42. Summary of interchange layouts and their relationships to existing interchanges with complexity
• Table 43. Summary of the possible combinations of interchange layout, signing alternative, and starting lane destination
• Table 44. Signing alternatives for layout A
• Table 45. Signing alternatives for layout L
• Table 46. Signing alternatives for layout C
• Table 47. Signing alternatives for layout E
• Table 48. The 12 interchange layout signing alternatives
• Table 49. Overview of the nine possible scenes (combinations of interchange layout, signing alternative, and starting lane destination)
• Table 50. Two possible orders of interchange layouts that participants might see
• Table 51. Overview of power analysis to assess minimally detectable differences in study metrics. Smallest Detectable Difference
• Table 52. Summary of participant experimental session activities and approximate duration of each
• Table 53. Variables extracted for analysis
• Table 54. Scenario details
• Table 55. Lane selection per decision point
• Table 56. ULCs across the interchange
• Table 57. Lane change data
• Table 58. Cases of inaccurate DP1 maneuvers prevented accurate DP2 maneuvers
• Table 59. Cases of negative ULCs
• Table 60. Cases of inaccurate DP1 maneuvers preventing accurate DP2 maneuvers
• Table 61. LSD: layout A, DP1
• Table 62. LSD: layout A, DP2
• Table 63. LSD: layout C, DP1
• Table 64. LSD: layout C, DP2
• Table 65. LSD: layout E, DP1
• Table 66. LSD: layout E, DP2
• Table 67. LSD: layout L, DP1
• Table 68. LSD: layout L, DP2
• Table 69. Signing alternatives with fewest ULCs
• Table 70. Selected interchanges for field data collection activities
• Table 71. Percentage of exiting traffic (site 11, eastbound)
• Table 72. Percentage of exiting traffic (site 11, westbound)
• Table 73. Percentage of exiting traffic (site 27)
• Table 74. Selected interchanges for site 31 data collection
• Table 75. Camera locations for site 31-1
• Table 76. Site 31-1—percentage of exiting traffic
• Table 77. Site 31-2—percentage of exiting traffic
• Table 78. Site 31-3—percentage of exiting traffic
• Table 79. Selected interchanges for site 43 data collection
• Table 80. Site 43—percentage of exiting traffic
• Table 81. Selected treatments for practice-ready recommendations
• Table 82. Organization of treatment summaries
• Table 83. Recommended source legend per indexing symbol
• Table 84. Practice and case summary for treatment 1
• Table 85. Practice and case summary for treatment 2
• Table 86. Practice and case summary for treatment 3
• Table 87. Recommended uses of currently approved guide sign arrows
• Table 88. Practice and case summary for treatment 4
• Table 89. Practice and case summary for treatment 5
• Table 90. Practice and case summary for treatment 6

List of Acronyms and Abbreviations