Driver Expectations When Navigating Complex Interchanges

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FOREWORD

Interchange navigation presents a range of challenges that are different from those associated with driving on continuous roads. For example, interchanges force drivers to make time-sensitive task demands (i.e., forced-paced tasks). More specifically, drivers at unfamiliar interchanges must read the available signage, observe pavement markings, and determine a path through the interchange before they reach the gore point. Additionally, driver errors at interchanges are often more difficult to correct since drivers may transfer to a grade-separated freeway, highway, or roadway that provides limited access points to return to the original roadway. Clear navigation signage is needed to guide drivers and reduce errors.

Although there has been previous research performed on signage in general, research specifically on interchange signage has been limited. There is little consensus on a best way to design signs for interchanges, and, in general, the current data on sign design is incomplete. The objective of this project was to begin addressing these information needs. This project yielded several overall conclusions related to driver expectations at complex interchanges. Namely, most drivers have problems at complex unfamiliar interchanges and feel stressed when they are surprised, are required to perform multiple lane changes in a short distance, or do not receive the information they expect. Several recommendations for sign designs are offered to help address these conditions. This report will be useful to traffic-safety researchers and traffic engineers responsible for highway design and public safety.

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

Technical Report Documentation Page

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

• Executive Summary
  • Background
  • Objectives
  • Project Overview
    • TASK 2-Literature Review
    • TASK 4-Gather Feedback from Drivers
    • TASK 7-Collect Experimental Data about Driver Expectations at Interchanges
  • Findings and Conclusions
    • How Do Expectations Affect Driver Behavior?
    • What are the Key Recommendations for Sign Design?
• CHAPTER 1. Introduction
  • Background
  • Objectives
  • Project Overview
    • TASK 2-Literature Review
    • TASK 3-Focus Group Protocol
    • TASK 4-Gather Feedback from Drivers
    • TASK 5-TASK Analysis
    • TASK 6-Data Collection Plan
    • TASK 7-Collect Experimental Data about Driver Expectations at Interchanges
  • Overview of Report
• CHAPTER 2. TASK 2-Literature Review
  • TASK 2 Methods
    • Literature Searches
    • Structured Literature Review Forms
  • TASK 2 Results
    • Definition of Driver Expectations
    • Driver Expectations Related to Roadway Elements
    • Variables
    • Applications of Expectations Research
  • TASK 2 Conclusions
    • Priority Research Gaps
    • Useful Metrics for Selecting Interchanges
    • Potential Scenarios for Focus Groups and TASK Analyses
• CHAPTER 3. TASK 4-Gather Feedback from Drivers
  • TASK 4 Methods
    • Participants
    • Procedures and Materials
    • Dynamic Scenarios
    • Selection of Interchanges
    • Focus Group Topics
    • Focus Group Questions
    • Session Timelines
    • Data Analysis Plan and Objectives
  • TASK 4 Results
    • Warm-Up Activity Results
    • Focus Group Discussion Results
    • Scenario 1
    • Scenario 1 Critical Point 1
    • Scenario 1 Critical Point 2
    • Scenario 1 Critical Point 3
    • Scenario 1 Key Themes
    • Scenario 2
    • Scenario 2 Critical Point 1
    • Scenario 2 Critical Point 2
    • Scenario 2 Critical Point 3
    • Scenario 2 Critical Point 4
    • Scenario 2 Key Themes
    • Scenario 3
    • Scenario 3 Critical Point 1
    • Scenario 3 Critical Point 2
    • Scenario 3 Key Themes
  • TASK 4 Conclusions
• CHAPTER 4. TASK 7-Collect Experimental Data about Driver Expectations at Interchanges
  • TASK 7 Methods
    • Participants
    • Procedures and Materials
    • Selection of Scenarios and Maneuvers
    • Data Analysis Plan and Objectives
  • TASK 7 Results
    • Topic 1: Option Lane Arrow Types and Driver Lane Preference
    • Topic 2: Option Lane Arrow Type and Separation.
    • Topic 3: Left Exit Notation
    • Topic 4: Two-Lane Exit with Two Destinations
    • Topic 5: Signing a Two-Lane Exit with a Downstream Split
    • Topic 6: Multilane Diagrammatic Signs
    • Topic 7: Signing Two Freeway Exits in Close Proximity
  • TASK 7 Conclusions
    • Key Conclusions
• CHAPTER 5. CONCLUSIONS AND RECOMMENDATIONS
  • CONCLUSIONS
    • How Do Expectations Affect Driver Behavior?
    • Recommendations for Sign Design
  • RECOMMENDATIONS
    • Systematically Apply Methodologies to Additional Interchanges with Existing Navigation Challenges
    • Conduct Research to Understand Why Up Arrows are More Effective at Communicating Permissible Lane Information
    • Conduct a More Comprehensive Analysis of Individual Response Patterns
• APPENDIX A. TASK 4 Response Booklet
• APPENDIX B. TASK 4 Moderator Guide
• APPENDIX C. TASK 4 Complete Responses from Warm-up Activity
• APPENDIX D. TASK 7 Moderator Guide
• APPENDIX E. TASK 7 Demographic Questionnaire
• APPENDIX F. TASK 7 Significance Test Tables
• ACKNOWLEDGEMENTS
• REFERENCES

LIST OF FIGURES

• Figure 1. Illustration. Overview of study tasks and information flow between tasks
• Figure 2. Illustration. Structured review form
• Figure 3. Illustration. Focus group video discussion method
• Figure 4. Photo. Interchange shown during the warm-up activity
• Figure 5. Illustration. Description of information elements in scenario overview diagrams
• Figure 6. Photo. Aerial view of scenario 1 roadway
• Figure 7. Illustration. Sign information and required vehicle maneuvers in scenario 1
• Figure 8. Photo. Image presented to drivers for discussion in scenario 1  critical point 1
• Figure 9. Illustration. Response option for scenario 1 critical point 1-two-lane split
• Figure 10. Illustration. Response option for scenario 1 critical point 1-single exit
• Figure 11. Illustration. Response option for scenario 1 critical point 1-two exits
• Figure 12. Illustration. Response option for scenario 1 critical point 1-two-lane exit
• Figure 13. Illustration. Response option for scenario 1 critical point 1-split with option lane
• Figure 14. Graph. Booklet response distribution for scenario 1 critical point 1 (number of responses (N) = 101)   
• Figure 15. Photo. Guide signs associated with scenario 1 critical point 1
• Figure 16. Photo. Image presented to drivers for discussion in scenario 1 critical point 2
• Figure 17. Illustration. Lane numbers for lane choice decisions in scenario 1  critical point 2
• Figure 18. Graph. Booklet response distribution for scenario 1 critical point 2 (N = 109)
• Figure 19. Photo. Guide signs associated with scenario 1 critical point 2
• Figure 20. Photo. Image presented to drivers for discussion in scenario 1 critical point 3
• Figure 21. Graph. Booklet response distribution for scenario 1 critical point 3 (N = 107)
• Figure 22. Photo. Guide signs associated with scenario 1 critical point 3
• Figure 23. Photo. Aerial view of scenario 2 roadway in Portland, OR
• Figure 24. Illustration. Sign information and required vehicle maneuvers in scenario 2
• Figure 25. Photo. Image presented to drivers for discussion in scenario 2 critical point 1
• Figure 26. Graph. Booklet response distribution for scenario 2 critical point 1 (N = 111)
• Figure 27. Photo. Guide signs associated with scenario 2 critical point 1
• Figure 28. Photo. Image presented to drivers for discussion in scenario 2 critical point 2
• Figure 29. Graph. Booklet response distribution for scenario 2 critical point 2 (N = 105)
• Figure 30. Photo. Guide sign associated with scenario 2 critical point 2
• Figure 31. Photo. Image presented to drivers for discussion in scenario 2 critical point 3
• Figure 32. Photo. Guide signs associated with scenario 2 critical point 3
• Figure 33. Photo. Image presented to drivers for discussion in scenario 2 critical point 4
• Figure 34. Graph. Booklet response distribution for scenario 2 critical point 4 (N = 109 to 111)
• Figure 35. Photo. Guide signs associated with scenario 2 critical point 4
• Figure 36. Illustration. Map of scenario 3 roadways and maneuver
• Figure 37. Photo. Aerial view of scenario 3 roadway
• Figure 38. Illustration. Sign information and required vehicle maneuvers in scenario 3
• Figure 39. Photo. Image presented to drivers for discussion in scenario 3 critical point 1
• Figure 40. Illustration. Lane numbers provided in response booklet for scenario 3 critical point 1
• Figure 41. Graph. Booklet response distribution for scenario 3 critical point 1 (N = 107)
• Figure 42. Photo. Guide signs associated with scenario 3 critical point 1
• Figure 43. Photo. Image presented to drivers for discussion in scenario 3 critical point 2
• Figure 44. Photo. Guide sign associated with scenario 3 critical point 2
• Figure 45. Illustration. Timeline of stimuli slide presentation
• Figure 46. Photo. Example test slide from topic 1-option lane to exit movement
• Figure 47. Photo. Example test slide from topic 1-through lane to exit movement
• Figure 48. Illustration. Topic 1-sign set A
• Figure 49. Illustration. Topic 1-sign set B
• Figure 50. Illustration. Topic 1-sign set C
• Figure 51. Photo. Example test slide from topic 2-through lane to exit movement
• Figure 52. Illustration. Topic 2-sign set A
• Figure 53. Illustration. Topic 2-sign set B
• Figure 54. Illustration. Topic 2-sign set C
• Figure 55. Illustration. Topic 2-sign set D
• Figure 56. Illustration. Example exit notation used in topic 3 questions-sign set A
• Figure 57. Illustration. Example exit notation used in topic 3 questions-sign set B
• Figure 58. Illustration. Example exit notation used in topic 3 questions-sign set C
• Figure 59. Photo. Example test slide from topic 3-lane 1 to through destination
• Figure 60. Photo. Example test slide from topic 3-lane 3 to left exit
• Figure 61. Illustration. Topic 3 question 1-sign set A
• Figure 62. Illustration. Topic 3 question 1-sign set B
• Figure 63. Illustration. Topic 3 question 1-sign set C
• Figure 64. Illustration. Topic 3 question 2-sign set A
• Figure 65. Illustration. Topic 3 question 2-sign set B
• Figure 66. Illustration. Topic 3 question 2-sign set C
• Figure 67. Illustration. Topic 3 question 3-sign set A
• Figure 68. Illustration. Topic 3 question 3-sign set B
• Figure 69. Illustration. Topic 3 question 3-sign set C
• Figure 70. Photo. Example test slide from topic 4
• Figure 71. Illustration. Topic 4-sign set A
• Figure 72. Illustration. Topic 4-sign set B
• Figure 73. Illustration. Topic 4-sign set C
• Figure 74. Illustration. Topic 4-sign set D
• Figure 75. Illustration. Topic 5 geometry split after a two-lane exit
• Figure 76. Photo. Example test slide from topic 5
• Figure 77. Illustration. Topic 5-sign set A
• Figure 78. Illustration. Topic 5-sign set B
• Figure 79. Illustration. Topic 5-sign set C
• Figure 80. Photo. Odd number of lanes (easy task difficulty)
• Figure 81. Photo. Odd number of lanes (hard task difficulty)
• Figure 82. Photo. Even number of lanes (easy task difficulty)
• Figure 83. Photo. Even number of lanes (hard task difficulty)
• Figure 84. Graph. Percent of correct responses by total number of roadway lanes for topic 6
• Figure 85. Illustration. Topic 7 roadway geometry-three destinations at two closely spaced exits
• Figure 86. Photo. Example test slide from topic 7
• Figure 87. Illustration. Topic 7-sign set A
• Figure 88. Illustration. Topic 7-sign set A2
• Figure 89. Illustration. Topic 7-sign set B
• Figure 90. Illustration. Topic 7-sign set B2
• Figure 91. Illustration. Topic 7-sign set C

LIST OF TABLES

• Table 1. Keywords used and number of records returned for literature searches
• Table 2. Independent variables found during the literature search categorized by variable type
• Table 3. Dependent variables found during the literature search categorized by study type
• Table 4. Demographic composition of each focus group
• Table 5. Complexity factors identified for each scenario
• Table 6. Summary of the most common responses given during the warm-up activity
• Table 7. Rank of booklet responses for scenario 3 critical point 2 (N = 92)
• Table 8. Demographic composition of each data collection session
• Table 9. Topic descriptions
• Table 10. Preferred lane responses for topic 1
• Table 11. Lane preference responses for topic 2
• Table 12. Sign placement comparisons between questions 2 and 3 sign sets
• Table 13. Lane selections for topic 4
• Table 14. Through lane selections for topic 4
• Table 15. Lane restriction responses for topic 5
• Table 16. Percent correct responses for easy/hard and odd/even conditions
• Table 17. Lane selections for topic 7
• Table 18. Summary of responses from focus group warm-up activity
• Table 19. Topic 1 comparisons between sign sets by movement
• Table 20. Topic 1 comparisons within sign sets by movement
• Table 21. Topic 2 comparisons between sign sets
• Table 22. Topic 3 comparisons between sign sets by question
• Table 23. Topic 3 comparisons between Questions 2 and 3
• Table 24. Topic 4 comparisons between sign sets
• Table 25. Topic 5 comparisons between sign sets
• Table 26. Topic 6 comparisons between easy and hard conditions within sign sets
• Table 27. Topic 7 comparisons for through movement condition between sign sets
• Table 28. Topic 7 comparisons for the first exit movement condition between sign sets
• Table 29. Topic 7 comparisons for second exit movement condition between sign sets