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Safety Effectiveness of Intersection
Left- and Right-Turn Lanes

FHWA-RD-02-089

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TechBrief

July 2002

Technical Report Documentation Page

1. Report No.
FHWA-RD-02-089		 2. Government Accession No.
3. Recipient's Catalog No.
4. Title and Subtitle
Safety Effectiveness of Intersection Left- and Right-Turn Lanes		 5. Report Date
July 2002
8. Performing Organization Report No.
104584.1.006
7. Author(s)
D.W. Harwood, K.M. Bauer, I.B. Potts, D.J. Torbic, K.R. Richard,
E.R. Kohlman Rabbani, E. Hauer, and L. Elefteriadou
9. Performing Organization Name and Address
Midwest Research Institute
425 Volker Boulevard
Kansas City, MO 64110-2299		 10. Work Unit No. (TRAIS)
11. Contract or Grant No.
DTFH61-96-C-00055
12. Sponsoring Agency Name and Address
Federal Highway Administration
Office of Safety Research and Development
6300 Georgetown Pike
McLean, Virginia 22101-2296		 13. Type of Report and Period Covered
Final Report
October 1996-July 2002
14. Sponsoring Agency Code
15. Supplementary Notes
COTR: Michael S. Griffith, HRDS-02
16. Abstract

This report presents the results of research that performed a well-designed before-after evaluation of the safety effects of providing left- and right-turn lanes for at-grade intersections. Geometric design, traffic control, traffic volume, and traffic accident data were gathered for a total of 280 improved intersections, as well as 300 similar intersections that were not improved during the study period. The types of improvement projects evaluated included installation of added left-turn lanes, added right-turn lanes, and extension of the length of existing left- or right-turn lanes. An observational before-after evaluation of these projects was performed using several alternative evaluation approaches. The three contrasting approaches to before-after evaluation used were the yoked comparison or matched-pair approach, the comparison group approach, and the Empirical Bayes approach. The research not only evaluated the safety effectiveness of left- and right-turn lane improvements, but also compared the performance of these three alternative approaches in making such evaluations. The research developed quantitative safety effectiveness measures for installation design improvements involving added left-turn lanes and added right-turn lanes. The research concluded that the Empirical Bayes method provided the most accurate and reliable results. Further use of this method is recommended.

17. Key Words
Intersection safety
Before-after evaluation
Left-turn lanes
Empirical Bayes
Right-turn lanes
Comparison group
Safety effectiveness		 18. Distribution Statement
No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161

19. Security Classif. (of this report)
Unclassified

 20. Security Classif. (of this page)
Unclassified		 21. No. of Pages

22. Price

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

 


Modern Metric Conversion Factors

Approximate conversions from SI Units
When You Know Multiply By To Find Symbol
LENGTH
millimeters 0.039 inches in
meters 3.28 feet ft
meters 1.09 yards yd
kilometers 0.621 miles mi
AREA
square millimeters 0.0016 square inches in2
square meters 10.764 square feet ft2
square meters 1.195 square yards yd2
hectares 2.47 acres ac
square kilometers 0.386 square miles mi2
VOLUME
milliliters 0.034 fluid ounces fl oz
liters 0.264 gallons gal
cubic meters 35.71 cubic feet ft3
cubic meters 1.307 cubic yards yd3
MASS
grams 0.035 ounces oz
kilograms 2.202 pounds lb
megagrams (or "metric ton") 1.103 short tons (2000 lb) T
TEMPERATURE (exact)
Celsius temperature 1.8C + 32 Fahrenheit temperature °F

Table of Contents

List of Figures

List of Tables

1. INTRODUCTION

2. LITERATURE REVIEW ON SAFETY EFFECTS OF INTERSECTION DESIGN ELEMENTS

Overview
Intersection Geometric Design Features
Traffic Control and Operational Features
Traffic Characteristics
Summary

3. SELECTION OF EVALUATION SITES

Evaluation Priorities for Intersection Improvement Types
Identification of Candidate Intersections
Selection of Improved or Treatment Sites
Selection of Comparison Sites
Number and Characteristics of Matching Improved and Comparison Sites
Selection of Reference Sites

4. DATA COLLECTION

Geometric Design and Traffic Control Data
Traffic Volume Data
Traffic Accident Data

5. EVALUATION PLAN

Target Accident Types and Locations
Accident Severity Levels
Evaluation Approaches
Before-After Evaluation with Yoked Comparisons
Before-After Evaluation with a Comparison Group
Before-After Evaluation with the Empirical Bayes Approach
Execution of the Evaluation Plan

6. EVALUATION RESULTS

Evaluation Results for Specific Safety Measures
Evaluation Results for Specific Project Types
Comparison of Alternative Evaluation Approaches
Projects Involving Added Left-Turn Lanes
Projects Involving Added Right-Turn Lanes
Projects Involving Added Left- and Right-Turn Lanes
Projects Involving Extension of the Length of Existing Turn Lanes
Supplementary Analysis Results
Recommended Accident Modification Factors
Economic Evaluations

7. CONCLUSIONS AND RECOMMENDATIONS

Conclusions
Recommendations

8. REFERENCES

Appendices

Appendix A—Summary of Intersection Safety Studies

Appendix B—Negative Binomial Regression Models

Appendix C—Detailed Evaluation Results

Appendix D—Field Data Collection for Geometric Design and Traffic Control Features

 

List of Figures

Figure 1. Target Area for Evaluation of an Intersection with a Right-Turn Lane Added on One Approach

Figure 2. Target Area for Evaluation of an Intersection with Right-Turn Lanes Added on Two Approaches

Figure 3. Target Area for Evaluation of an Intersection with a Left-Turn Lane Added on One Approach

Figure 4. Plot of Observed vs. Expected Accident Frequencies

Figure 5. Typical Regression Relationship for Predicting Intersection Accident Frequency as a Function of Entering Traffic Volume

Figure 6. Comparison of Accident Experience for Treatment and Comparison Groups for Rural Unsignalized Intersections at Which Left-Turn Lanes Were Added

Figure 7. Use of Regression Relationship in the EB Approach

 

List of Tables

Table 1. Intersection Features Addressed in the Literature Review

Table 2. Accident Modification Factors for Installation of Left-Turn Lanes on the Major-Road Approaches to Intersection on Two-Lane Rural Highways

Table 3. Summary of Research Results Concerning the Safety Effectiveness of Installing Left-Turn Lanes

Table 4. Accident Modification Factors for Installation of Right-Turn Lanes on the Major-Road Approaches to Intersection on Two-Lane Rural Highways

Table 5. Summary of Research Results Concerning the Safety Effectiveness of Installing Right-Turn Lanes

Table 6. Number of Improved Intersection Sites by Area Type and State

Table 7. Number of Improved Sites at Rural Intersections

Table 8. Number of Improved Sites at Urban Intersections

Table 9. Number of Improved Intersections and Number of Turn-Lanes Added or Extended in Intersection Improvement Projects

Table 10. Year Completed for Projects at Improved Intersections

Table 11. Number of Matched Pairs of Improved and Comparison Sites by Area Type and State

Table 12. Number of Matched Pairs of Improved and Comparison Sites at Rural Intersections

Table 13. Number of Matched Pairs of Improved and Comparison Sites at Urban Intersections

Table 14. Number of Improved Intersections and Number of Turn-Lanes Added in Projects at Improved Sites with Matched Comparison Sites in Candidate Intersection Improvement Projects

Table 15. Completion Date for Intersection Improvement Projects With Matched Comparison Sites

Table 16. Number of Comparison and Reference Sites by Area Type, Traffic Control Type, and State

Table 17. ADT Volumes for All Improved and Comparison/Reference Sites

Table 18. ADT Volumes for Matched Improved and Comparison Sites

Table 19. Summary of Accident Database

Table 20. Safety Performance of Matched Improved and Comparison Sites at Rural Intersections

Table 21. Safety Performance of Matched Improved and Comparison Sites at Urban Intersections

Table 22. Accident Data Layout for a Before-After Evaluation with Yoked Comparisons

Table 23. Calculations of 2 Treatment, 2 Homogeneity, and 2 Total for Before-After Evaluation with Yoked Comparisons

Table 24. Accident Data Layout for Before-After Evaluation with Comparison Group

Table 25. Observed and Expected Accident Counts

Table 26. Comparison of Accident Frequency Time Series for Treatment and Control Groups in the Time Period Before Improvement of the Treatment Sites

Table 27. Accident Data Layout for Before-After Evaluation with the Empirical Bayes Approach

Table 28. Evaluation Results for Total Intersection Accidents at Four-Leg Intersections

Table 29. Evaluation Results for Fatal and Injury Intersection Accidents at Four-Leg Intersections

Table 30. Evaluation Results for Project-Related Intersection Accidents at Four-Leg Intersections

Table 31. Evaluation Results for Project-Related Fatal and Injury Accidents at Four-Leg Intersections

Table 32. Evaluation Results for Total Accidents on Individual Intersection Approaches at Four-Leg Intersections

Table 33. Evaluation Results for Fatal and Injury Accidents on Individual Intersection Approaches at Four-Leg Intersections

Table 34. Evaluation Results for Project-Related Accidents on Individual Intersection Approaches at Four-Leg Intersections

Table 35. Evaluation Results for Total Intersection Accidents at Three-Leg Intersections

Table 36. Evaluation Results for Fatal and Injury Intersection Accidents at Three-Leg Intersections

Table 37. Evaluation Results for Project-Related Intersection Accidents at Three-Leg Intersections

Table 38. Evaluation Results for Total Accidents on Individual Intersection Approaches at Three-Leg Intersections

Table 39. Evaluation Results for Fatal and Injury Accidents on Individual Intersection Approaches at Three-Leg Intersections

Table 40. Evaluation Results for Project-Related Accidents on Individual Intersection Approaches at Three-Leg Intersections

Table 41. Evaluation Results for Projects Involving Added Left-Turn Lanes at Four-Leg Intersections

Table 42. Evaluation Results for Projects Involving Added Right-Turn Lanes at Four-Leg Intersections

Table 43. Evaluation Results for Projects Involving Added Left- and Right-Turn Lanes at Four-Leg Intersections

Table 44. Evaluation Results for Projects Involving Extension of the Length of Existing Turn Lanes at Four-Leg Intersections

Table 45. Evaluation Results for Projects Involving Added Left-Turn Lanes at Three-Leg Intersections

Table 46. Evaluation Results for Projects Involving Added Right-Turn Lanes at Three-Leg Intersections

Table 47. Comparison of Evaluation Approaches

Table 48. Final Evaluation Results Involving Added Left-Turn Lanes for Four-Leg Intersections

Table 49. Final Evaluation Results Involving Added Left-Turn Lanes for Three-Leg Intersections

Table 50. Final Evaluation Results for Projects Involving Added Right-Turn Lanes for Four-Leg Intersections

Table 51. Final Evaluation Results for Projects Involving Added Right-Turn Lanes for Three-Leg Intersections

Table 52. Final Evaluation Results for Projects Involving Added Left- and Right-Turn Lanes for Four-Leg Intersections

Table 53. Comparison of Safety Effectiveness of Added Left-Turn Lanes With Curbed and Painted Channelization

Table 54. Comparison of Safety Effectiveness of Added Left-Turn Lanes With Protected and Protected/Permissive Signal Phasing

Table 55. Recommended Accident Modification Factors for Installation of Left-Turn Lanes on the Major-Road Approaches to Rural Intersections

Table 56. Recommended Accident Modification Factors for Installation of Left-Turn Lanes on the Major-Road Approaches to
Urban Intersections

Table 57. Recommended Accident Modification Factors for Installation of Right-Turn Lanes on the Major-Road Approaches to Rural and Urban Intersections

Table 58. Economic Evaluation for Rural Three-Leg Unsignalized Intersections with Minor-Road ADT Equal to 10 Percent of Major-Road ADT

Table 59. Economic Evaluation for Rural Three-Leg Unsignalized Intersections with Minor-Road ADT Equal to 50 Percent of Major-Road ADT

Table 60. Economic Evaluation for Rural Four-Leg Unsignalized Intersections With Minor-Road ADT Equal to 10 Percent of Major-Road ADT

Table 61. Economic Evaluation for Rural Four-Leg Unsignalized Intersections With Minor-Road ADT Equal to 50 Percent of Major-Road ADT

Table 62. Economic Evaluation for Urban Four-Leg Unsignalized Intersections With Minor-Road ADT Equal to 10 Percent of Major-Road ADT

Table 63. Economic Evaluation for Urban Four-Leg Unsignalized Intersections With Minor-Road ADT Equal to 50 Percent of Major-Road ADT

Table 64. Economic Evaluation for Urban Four-Leg Signalized Intersections With Minor-Road ADT Equal to 25 Percent of Major-Road ADT

Table 65. Economic Evaluation for Urban Four-Leg Signalized Intersections With Minor-Road ADT Equal to 50 Percent of Major-Road ADT

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