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FHWA-RD-02-089
PDF Version (1.48 mb)
TechBrief
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 |
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8. Performing Organization Report No. 104584.1.006 |
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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 |
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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 |
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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 |
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14. Sponsoring Agency Code |
15. Supplementary Notes COTR: Michael S. Griffith, HRDS-02 |
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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 |
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19. Security Classif. (of this report) |
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
When You Know | Multiply By | To Find | Symbol |
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LENGTH |
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millimeters | 0.039 | inches | in |
meters | 3.28 | feet | ft |
meters | 1.09 | yards | yd |
kilometers | 0.621 | miles | mi |
AREA |
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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 |
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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 |
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grams | 0.035 | ounces | oz |
kilograms | 2.202 | pounds | lb |
megagrams (or "metric ton") | 1.103 | short tons (2000 lb) | T |
TEMPERATURE (exact) |
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Celsius temperature | 1.8C + 32 | Fahrenheit temperature | °F |
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
Geometric Design and Traffic Control Data
Traffic Volume Data
Traffic Accident Data
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
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
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
Figure 1. Target Area for Evaluation of an Intersection with a Right-Turn Lane Added on One Approach
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 7. Use of Regression Relationship in the EB Approach
Table 1. Intersection Features Addressed in the Literature Review
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 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 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 24. Accident Data Layout for Before-After Evaluation with Comparison Group
Table 25. Observed and Expected Accident Counts
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 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 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 45. Evaluation Results for Projects Involving Added Left-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
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