SAFETY PREDICTION METHODOLOGY AND ANALYSIS …

1 Project No. 17-45 Copy No. SAFETY PREDICTION METHODOLOGY . AND ANALYSIS tool . FOR FREEWAYS AND INTERCHANGES. FINAL REPORT. Prepared For National Cooperative Highway Research Program Transportation Research Board of The National Academies TRANSPORTATION RESEARCH BOARD. OF THE NATIONAL ACADEMIES. PRIVILEGED DOCUMENT. This report, not released for publication, is furnished only for review to members of or participants in the work of the CRP. This report is to be regarded as fully privileged, and dissemination of the information included herein must be approved by the CRP. Texas Transportation Institute Texas A&M University In Association with: CH2M-Hill May 2012. ACKNOWLEDGMENT OF SPONSORSHIP. This work was sponsored by the American Association of State Highway and Transportation Officials, in cooperation with the Federal Highway Administration, and was conducted in the National Cooperative Highway Research Program which is administered by the Transportation Research Board of the National Academies.

2 DISCLAIMER. This is an uncorrected draft as submitted by the research agency. The opinions and conclusions expressed or implied in the report are those of the research agency. They are not necessarily those of the Transportation Research Board, the National Academies, or the program sponsors. NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM. Project 17-45. SAFETY PREDICTION METHODOLOGY and ANALYSIS tool for Freeways and Interchanges James A. Bonneson Srinivas Geedipally Michael P. Pratt Texas Transportation Institute College Station, Texas Dominique Lord Texas A&M University College Station, Texas Subject Areas Highway and Facility Design Highway Operations, Highway SAFETY Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the Federal Highway Administration Transportation Research Board of the National Academies Washington, May 2012.

3 CONTENTS. page LIST OF FIGURES .. vi LIST OF TABLES .. ix ACKNOWLEDGMENTS .. xiii ABSTRACT .. xiv EXECUTIVE SUMMARY .. 1. CHAPTER 1: INTRODUCTION .. 3. Research Objectives .. 3. Research Scope .. 3. Organization of this Report .. 4. CHAPTER 2: LITERATURE REVIEW .. 5. Background .. 5. Freeway and Interchange SAFETY .. 12. CHAPTER 3: FRAMEWORK FOR SAFETY PREDICTION .. 57. Overview of HSM METHODOLOGY .. 57. Prioritized List of SPFs and CMFs .. 60. CHAPTER 4: DATABASE DEVELOPMENT .. 69. Data Collection 69. Database Summary .. 79. CHAPTER 5: PREDICTIVE MODEL FOR FREEWAY SEGMENTS .. 101. Background .. 102. CMF 108. METHODOLOGY .. 113. Model Calibration for FI Crashes .. 119. Model Calibration for PDO Crashes .. 158. Nomenclature .. 177. CHAPTER 6: PREDICTIVE MODEL FOR RAMP SEGMENTS .. 183. Background .. 184. CMF 188. METHODOLOGY .

4 196. Model Calibration for FI Crashes .. 199. Model Calibration for PDO Crashes .. 223. Nomenclature .. 234. CHAPTER 7: PREDICTIVE MODEL FOR CROSSROAD RAMP 237. Background .. 238. CMF 242. METHODOLOGY .. 254. Model Calibration for FI Crashes .. 259. Model Calibration for PDO Crashes .. 294. Nomenclature .. 318. CHAPTER 8: SEVERITY DISTRIBUTION FUNCTIONS .. 321. Literature 321. Freeway Segments .. 323. Ramp Segments .. 336. Crossroad Ramp 342. CHAPTER 9: CONCLUSIONS AND RECOMMENDATIONS .. 351. v REFERENCES .. 353. APPENDIX A Practitioner Interviews APPENDIX B Database Enhancement APPENDIX C Proposed HSM Freeways Chapter APPENDIX D Proposed HSM Ramps Chapter APPENDIX E Proposed HSM Appendix B for Part C. APPENDIX F Algorithm Description LIST OF FIGURES. page Figure 1. Typical interchange types.. 7. Figure 2. Distribution of interchange types used in the United 7.

5 Figure 3. Typical diamond and parclo interchange types.. 8. Figure 4. Typical ramp 9. Figure 5. Freeway and interchange design components.. 10. Figure 6. Disaggregated alignment for a diamond ramp.. 12. Figure 7. Ramp-configuration-based SPFs based on total crashes.. 17. Figure 8. Relationship between CMF value and ramp radius based on total crashes.. 19. Figure 9. Relationship between CMF value and ramp lane width based on total crashes.. 20. Figure 10. Relationship between ramp crash frequency and crash type based on total crashes.. 21. Figure 11. Typical speed-change lanes.. 22. Figure 12. Relationship between CMF value and acceleration length based on total crashes.. 25. Figure 13. Relationship between CMF value and deceleration length based on total crashes.. 26. Figure 14. Relationship between crash rate, traffic demand, and number of lanes.

6 29. Figure 15. Freeway segment SPFs based on FI crashes.. 30. Figure 16. Relationship between CMF value and curve radius.. 32. Figure 17. Relationship between CMF value and lane width based on total crashes.. 33. Figure 18. Illustrative interaction between shoulder width and lane width.. 34. Figure 19. Relationship between CMF value and outside shoulder width based on total crashes.. 34. Figure 20. Relationship between CMF value and inside shoulder width based on total crashes. 35. Figure 21. Relationship between CMF value and median width.. 35. Figure 22. Relationship between CMF value and horizontal clearance based on FI crashes.. 37. Figure 23. Percent of lane changes as a function of distance from ramp gore.. 39. Figure 24. Total crash rate as a function of distance from ramp gore.. 40. Figure 25. Relationship between CMF value and distance from gore.

7 41. Figure 26. Relationship between CMF value and weaving length.. 42. Figure 27. Relationship between CMF value and interchange spacing.. 43. Figure 28. Relationship between total crash rate and volume-to-capacity ratio for highways.. 45. Figure 29. Relationship between total crash rate and volume-to-capacity ratio for freeways.. 45. Figure 30. Relationship between traffic demand, crash type, and total crash frequency.. 46. Figure 31. Relationship between CMF value and volume-to-capacity ratio.. 47. Figure 32. High-occupancy vehicle travel direction types.. 49. Figure 33. Relationship between FI crash rate and speed differential.. 51. Figure 34. SPF for two interchange types based on total crashes.. 53. Figure 35. Designs to discourage wrong-way maneuvers.. 56. vi Figure 36. Highway SAFETY Manual predictive method.. 58. Figure 37.

8 Ramp terminal configurations.. 91. Figure 38. Illustrative freeway facility ANALYSIS 103. Figure 39. Hourly volume distribution for two freeway segments.. 110. Figure 40. Proportion-of-volume statistic for freeway segments in three states.. 111. Figure 41. Relationship between crash rate and side friction demand.. 112. Figure 42. Weaving section types.. 114. Figure 43. Weaving section length measurement.. 115. Figure 44. Predicted vs. reported multiple-vehicle freeway FI crashes.. 135. Figure 45. Predicted vs. reported single-vehicle freeway FI crashes.. 137. Figure 46. Predicted vs. reported ramp-entrance-related FI crashes.. 138. Figure 47. Predicted vs. reported ramp-exit-related FI crashes.. 139. Figure 48. Calibrated freeway horizontal curve CMF for FI crashes.. 141. Figure 49. Calibrated freeway lane width CMF for FI crashes.

9 142. Figure 50. Calibrated freeway outside shoulder width CMF for FI crashes.. 143. Figure 51. Calibrated freeway inside shoulder width CMF for FI crashes.. 144. Figure 52. Calibrated freeway median width CMF for FI crashes.. 145. Figure 53. Calibrated freeway outside clearance CMF for FI crashes.. 147. Figure 54. Lane change CMF as a function of distance from ramp gore.. 149. Figure 55. Lane change CMF for segments between a pair of interchanges.. 150. Figure 56. Average CMF value for FI crashes as a function of weaving section length.. 151. Figure 57. Calibrated freeway ramp entrance CMF for right-side ramps and FI crashes.. 152. Figure 58. Calibrated freeway ramp exit CMF for right-side ramps and FI crashes.. 153. Figure 59. Calibrated freeway high-volume CMF for FI crashes.. 154. Figure 60. Freeway FI model components.

10 155. Figure 61. Freeway FI model.. 156. Figure 62. Predicted vs. reported multiple-vehicle freeway PDO crashes.. 161. Figure 63. Predicted vs. reported single-vehicle freeway PDO crashes.. 163. Figure 64. Predicted vs. reported ramp-entrance-related PDO crashes.. 164. Figure 65. Predicted vs. reported ramp-exit-related PDO 165. Figure 66. Calibrated freeway horizontal curve CMF for PDO 167. Figure 67. Calibrated freeway outside shoulder width CMF for PDO crashes.. 168. Figure 68. Calibrated freeway inside shoulder width CMF for PDO crashes.. 168. Figure 69. Calibrated freeway median width CMF for PDO crashes.. 169. Figure 70. Calibrated freeway outside barrier CMF for PDO crashes.. 171. Figure 71. Average CMF value for PDO crashes as a function of weaving section length.. 173. Figure 72. Calibrated freeway ramp entrance CMF for right-side ramps and PDO crashes.