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Publication Number: FHWA-HRT-08-051
Date: June 2008

Surrogate Safety Assessment Model and Validation: Final Report

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Table of Contents

FOREWORD

The safety of intersections, interchanges, and other traffic facilities is most often assessed by tracking and analyzing police-reported motor vehicle crashes over time. Given the infrequent and random nature of crashes, this process is slow to reveal the need for remediation of either the roadway design or the flow-control strategy. This process is also not applicable to assess new designs that have yet to be built, or to assess new flow-control strategies before they are employed on-site.

This document is a final report on research and development of an alternative safety-assessment approach utilizing conflict analysis—analyzing the frequency and character of narrowly averted vehicle-to-vehicle collisions in traffic—as a surrogate measure of actual crash data. A software prototype has been developed to automate conflict analysis of vehicle trajectory data, which can now be exported from the traffic simulation software of four vendors who collaborated on the project. The majority of the report describes validation testing conducted to evaluate the efficacy of this approach. The findings may be of interest to transportation engineers, safety engineers, researchers, simulation designers, and firms providing simulation or intersection design services.

Michael Trentacoste

Director, Office of Safety

Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

TECHNICAL REPORT DOCUMENTATION PAGE

1. Report No.
FHWA-HRT-08-051
2. Government Accession No. 3. Recipient’s Catalog No.
4. Title and Subtitle
Surrogate Safety Assessment Model and Validation: Final Report
5. Report Date
June 2008
6. Performing Organization Code:
7. Author(s)
Douglas Gettman, Lili Pu, Tarek Sayed, and Steve Shelby
8. Performing Organization Report No.
9. Performing Organization Name and Address
Siemens Energy & Automation, Inc. Business Unit Intelligent Transportation Systems 6375 E. Tanque Verde, Suite 170 Tucson, AZ 85715
10. Work Unit No.
11. Contract or Grant No.
DTFH61-03-C-00129
12. Sponsoring Agency Name and Address
Office of Safety RD&T Turner Fairbank Highway Research Center Federal Highway Administration 6300 Georgetown Pike McLean, VA 22101-2296
13. Type of Report and Period Covered
Final Report: September 2003–November 2007
14. Sponsoring Agency Code
HRDS-05
15. Supplementary Notes
FHWA Contracting Officer’s Technical Representative (COTR): Joe Bared
16. Abstract
Safety of traffic facilities is most often measured by counting the number (and severity) of crashes that occur. It is not possible to apply such a measurement technique to traffic facility designs that have not yet been built or deployed in the real world. This project has resulted in the development of a software tool for deriving surrogate safety measures for traffic facilities from data output by traffic simulation models. This software is referred to as SSAM—an acronym for the Surrogate Safety Assessment Model. The surrogate measures developed in this project are based on the identification, classification, and evaluation of traffic conflicts that occur in the simulation model. By comparing one simulated design case with another, this software allows an analyst to make statistical judgments about the relative safety of the two designs. An open-standard vehicle trajectory data format was designed, and support for this format has been added as an output option by four simulation model vendors/developers— PTV (VISSIM), TSS (AIMSUN), Quadstone (Paramics), and Rioux Engineering (TEXAS). Eleven “theoretical” validation tests were performed to compare the surrogate safety assessment results of pairs of simulated design alternatives. In addition, a field validation exercise was completed to compare the output from SSAM with real-world crash records. Eighty-three intersections from British Columbia, Canada were modeled in VISSM and simulated under AM-peak traffic conditions. The processed conflict results were then compared with the crash records in a number of different statistical validation tests. Last, sensitivity analysis was performed to identify differences between the SSAM-related outputs of each simulation model vendor’s system on the same traffic facility designs. These comparative analyses provide some guidance to the relative use of surrogate measures data from each simulation system. The SSAM software tool and user manual (FHWA-HRT08-050) are available to the public at no cost from FHWA.
17. Key Words
Surrogate measures, safety, traffic simulation, validation, traffic conflicts, conflicts, crashes, accidents, prediction
18. Distribution Statement
No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161.
19. Security Classif. (of this report)
Unclassified
20. Security Classif. (of this page)
Unclassified

21. No. of Pages
322

22. Price

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


SI* (Modern Metric) Conversion Factors


TABLE OF CONTENTS

Chapter 1. Introduction

  1. Background
  2. Safety Prediction Models
  3. Statistical Challenges
  4. Surrogate Safety Measures
  5. Traffic Conflicts
  6. Surrogate Safety Assessment Model
  7. Report Organization

Chapter 2. SSAM Software

  1. SSAM Workflow
  2. Conflict Identification Algorithms
  3. Step 1
  4. Step 2
  5. Step 3
  6. Step 4
  7. Terms and Definitions
  8. Definitions of Surrogate Measures Computed by SSAM

Chapter 3. Theoretical Validation

Chapter 4. Field Validation

Chapter 5. Sensitivity Analysis

Chapter 6. Conclusion

Appendix A. Description of Canadian Intersections

Appendix B. Abrupt Lane-Change Behavior

Appendix C. Conflicts Analysis Results

Appendix D. Gap Configuration and Conflict Frequency

References

LIST OF FIGURES

Figure 1. Illustration. SSAM Operational Concept
Figure 2. Screen Capture. SSAM User Interface after Launching
Figure 3. Screen Capture. SSAM User Interface with Case File Defined
Figure 4. Screen Capture. SSAM User Interface with Conflicts Tab Selected
Figure 5. Screen Capture. SSAM User Interface with Summary Tab Selected
Figure 6. Screen Capture. SSAM User Interface with Filter Tab Selected
Figure 7. Screen Capture. CSV File from SSAM
Figure 8. Illustration. Illustration of Zone Grid
Figure 9. Illustration. Illustration of Vehicle Path
Figure 10. Illustration. DIS1 and DIS2
Figure 11. Illustration. Updated DIS1 and DIS2 when Old DIS1 > DIS2
Figure 12. Illustration. Projection Point when DIS1 < DIS2
Figure 13. Illustration. Checking Conflict Between Two Vehicles at MaxTTC
Figure 14. Illustration. Checking Conflict Between Two Vehicles at TTC = 1.3 (Vehicles No Longer in Conflict)
Figure 15. Illustration. Conflict Angle
Figure 16. Illustration. Clock Angle
Figure 17. Equation. Accident Prediction Model for an Urban, Four-Leg, Signalized Intersection
Figure 18. Equation. Accident Prediction Model for an Urban, Four-Leg, Stop-Controlled Intersection
Figure 19. Equation. Accident Prediction Model for a Three-Leg, Signalized Intersection
Figure 20. Equation. Accident Prediction Model for an Urban, Three-Leg, Stop-Controlled Intersection
Figure 21. Equation. Accident Prediction Model for a Diamond Interchange
Figure 22. Equation. Entry-Circulating Roundabout Accident Prediction Model
Figure 23. Equation. Accident Prediction Model for Roundabout Approaches
Figure 24. Equation. Single-Vehicle Accident Model for Roundabouts
Figure 25. Equation. Other Vehicle Accident Prediction Model for Roundabouts
Figure 26. Equation. Pedestrian Accident Prediction Model for Roundabouts
Figure 27. Equation. Spearman Rank Correlation Coefficient
Figure 28. Equation. Using K-Factors to Scale Hourly Volume to Daily Volume
Figure 29. Screen Capture. Intersection Geometry for Testing Control Logic
Figure 30. Illustration. Timing Plan for Permitted Left Turn in Low Volumes
Figure 31. Illustration. Timing Plan for Protected Left Turn in Low Volumes
Figure 32. Illustration. Timing Plan for Permitted Left Turn in Medium Volumes
Figure 33. Illustration. Timing Plan for Protected Left Turn in Medium Volumes
Figure 34. Illustration. Timing Plan for Permitted Left Turn in High Volumes
Figure 35. Illustration. Timing Plan for Protected Left Turn in High Volumes
Figure 36. Screen Capture. Exclusive Left-Turn Lane
Figure 37. Screen Capture. Shared Use Left-Turn and Through Lane
Figure 38. Illustration. Timing Plan for Intersection with Left-Turn Bay in Low Volumes
Figure 39. Illustration. Timing Plan for Intersection without Left-Turn Bay in Low Volumes
Figure 40. Illustration. Timing Plan for Intersection with Left-Turn Bay in Medium Volumes
Figure 41. Illustration. Timing Plan for Intersection without Left-Turn Bay in Medium Volumes
Figure 42. Illustration. Timing Plan for Intersection with Left-Turn Bay in High Volumes
Figure 43. Illustration. Timing Plan for Intersection without Left-Turn Bay in High Volumes
Figure 44. Screen Capture. Intersection with Right-Turn Bay
Figure 45. Screen Capture. Intersection without Right-Turn Bay
Figure 46. Illustration. Timing Plan for Intersection with Right-Turn Bay in Low Volumes
Figure 47. Illustration. Timing Plan for Intersection without Right-Turn Bay in Low Volumes
Figure 48. Illustration. Timing Plan for Intersection with Right-Turn Bay in Medium Volumes
Figure 49. Illustration. Timing Plan for Intersection without Right-Turn Bay in Medium Volumes
Figure 50. Illustration. Timing Plan for Intersection with Right-Turn Bay in High Volumes
Figure 51. Illustration. Timing Plan for Intersection without Right-Turn Bay in High Volumes
Figure 52. Screen Capture. Intersection with Leading Left Turn
Figure 53. Screen Capture. Intersection with Lagging Left Turn
Figure 54. Illustration. Timing Plan for Intersection with Lag Left Turn in Low Volumes (Cycle: 80; Split: 22, 17, 22, and 19)
Figure 55. Illustration. Timing Plan for Intersection with Lead Left Turn in Low Volumes (Cycle: 80; Split: 17, 22, 22, and 19)
Figure 56. Illustration. Timing Plan for Intersection with Lag Left Turn in Medium Volumes (Cycle: 80; Split: 33, 17, 15, and 15)
Figure 57. Illustration. Timing Plan for Intersection with Lead Left Turn in Medium Volumes (Cycle: 80; Split: 17, 33, 15, and 15)
Figure 58. Illustration. Timing Plan for Intersection with Lag Left Turn in High Volumes (Cycle: 75; Split: 20, 11, 23, and 21)
Figure 59. Illustration. Timing Plan for Intersection with Lead Left Turn in High Volumes (Cycle: 75; Split: 11, 20, 23, and 21)
Figure 60. Illustration. Diamond Interchange
Figure 61. Screen Capture. Three-Phase Sequencing Signal Control for Diamond Interchange
Figure 62. Screen Capture. Four-Phase Sequencing Signal Control for Diamond Interchange
Figure 63. Screen Capture. Intersection for Diamond Interchange with Three-Phase Test
Figure 64. Screen Capture. Intersection for Diamond Interchange with Four-Phase Test

Figure 65. Screen Capture. Timing Plan for Three-Phase Diamond Interchange in Low Volumes

Figure 66. Screen Capture. Timing Plan for Four-Phase Diamond Interchange in Low Volumes

Figure 67. Screen Capture. Timing Plan for Three-Phase Diamond Interchange in Medium Volumes

Figure 68. Screen Capture. Timing Plan Four-Phase Diamond Interchange in Medium Volumes

Figure 69. Screen Capture. Timing Plan for Three-Phase Diamond Interchange in High Volumes
Figure 70. Screen Capture. Timing Plan for Four-Phase Diamond Interchange in High Volumes
Figure 71. Screen Capture. Single-Point Urban Interchange
Figure 72. Screen Capture. Phase 1
Figure 73. Screen Capture. Phase 2
Figure 74. Screen Capture. Phase 3
Figure 75. Screen Capture. Diamond Interchange in VISSIM
Figure 76. Screen Capture. Link-Connector View of Diamond Interchange Model in VISSIM
Figure 77. Screen Capture. SPUI in VISSIM
Figure 78. Illustration. Timing Plan for Diamond Interchange in Low Volumes
Figure 79. Illustration. Timing Plan for SPUI in Low Volumes
Figure 80. Illustration. Timing Plan for Diamond Interchange in Medium Volumes

Figure 81. Illustration. Timing Plan SPUI in Medium Volumes

Figure 82. Illustration. Timing Plan for Diamond Interchange in High Volumes
Figure 83. Illustration. Timing Plan for SPUI in High Volumes
Figure 84. Illustration. Potential Conflict Points for 2 x 2-Lane Intersections. (14)
Figure 85. Screen Capture. Conventional Nonsignalized Intersection
Figure 86. Screen Capture. Offset T-Intersection
Figure 87. Illustration. Mid-Block U-Turn at Signalized Intersection
Figure 88. Screen Capture. Conventional Intersection in VISSIM
Figure 89. Screen Capture. Intersection with Median U-Turn in VISSIM
Figure 90. Illustration. Timing Plan Conventional Intersection in Low Volumes (Cycle: 80; Split: 12, 28, 10, 10)

Figure 91. Illustration. Timing Plan for Median U Turn in Low Volumes
Figure 92. Illustration. Timing Plan for Conventional Intersection in Medium Volumes (Cycle: 80; Split: 12, 28, 10, 10) Figure 93. Illustration. Timing Plan for Median U Turn in Medium Volumes (Cycle: 80; Split: 49, 9.5, 6.5, 21)
Figure 94. Illustration. Timing Plan for Conventional Intersection in High Volumes (Cycle: 80; Split: 12, 28, 10, 10)

Figure 95. Illustration. Timing Plan for Median U Turn in High Volumes (Cycle: 80; Split: 49, 9.5, 6.5, 21) ..
Figure 96. Illustration. Conflict Points for Intersections with Four Single-Lane Approaches.(23)
Figure 97. Illustration. Conflict Points for T-Intersections with Single-Lane Approaches. (23)
Figure 98. Screen Capture. Conventional Intersection in AIMSUN
Figure 99. Screen Capture. Four-Approach Roundabout in AIMSUN
Figure 100. Screen Capture. Timing Plan for Conventional Intersection in Low Volumes
Figure 101. Screen Capture. Timing Plan for Conventional Intersection in Medium Volumes
Figure 102. Screen Capture. Timing Plan for Conventional Intersection in High Volumes
Figure 103. Screen Capture. T-Intersection in AIMSUN
Figure 104. Screen Capture. Three-Approach Roundabout in AIMSUN
Figure 105. Illustration. Timing Plan for T-Intersection in Low Volumes
Figure 106. Illustration. Timing Plan for T-Intersection in Medium Volumes
Figure 107. Illustration. Timing Plan for T-Intersection in High Volumes
Figure 108. Illustration. Double Roundabout
Figure 109. Screen Capture. Diamond Interchange in AIMSUN
Figure 110. Screen Capture. Double Roundabout in AIMSUN
Figure 111. Screen Capture. Timing Plan for Four-Phase Diamond Interchange in Low Volumes
Figure 112. Screen Capture. Timing Plan for Four-Phase Diamond Interchange in Medium Volumes
Figure 113. Screen Capture. Timing Plan for Four-Phase Diamond Interchange in High Volumes
Figure 114. Equation. Spearman Rank Correlation Coefficient
Figure 115. Equation. Standard Deviation for Paired Data Samples
Figure 116. Equation. Critical Z-Value
Figure 117. Equation. Pearson Chi-Squared Goodness of Fit Measure
Figure 118. Equation. Scaled Deviance Measure
Figure 119. Equation. R-Squared Goodness of Fit Measure
Figure 120. Equation. Calculation of Gamma Parameters for Prior Distribution
Figure 121. Equation. 50th Percentile
Figure 122. Equation. Safety Estimate
Figure 123. Equation. Variance
Figure 124. Equation. Gamma Parameters for Posterior Distribution
Figure 125. Equation. Probability Density Function for Posterior Distribution
Figure 126. Equation. Criterion for a Crash Prone Site Rating
Figure 127. Screen Capture. First Taper Modeling Configuration
Figure 128. Screen Capture. Second Taper Modeling Configuration
Figure 129. Screen Capture. Queuing Problem Due to the Second Taper Configuration
Figure 130. Equation. Normal Linear Regression Model for Crashes as a Function of Conflicts
Figure 131. Equation. Nonlinear Regression Model for Crashes as a Function of Conflicts
Figure 132. Graph. Effect of Redefining the Priority Rules on Total Conflicts (Including Simulated Crashes)
Figure 133. Graph. Effect of Redefining the Priority Rules on Total Conflicts (Excluding Simulated Crashes)
Figure 134. Photo. GoogleTM Map View of Briarcliff Rd & North Druid Hills Rd
Figure 135. Screen Capture. VISSIM Model of Briarcliff Rd & North Druid Hills Rd
Figure 136. Screen Capture. AIMSUN Model of Briarcliff Rd & North Druid Hills Rd
Figure 137. Screen Capture. PARAMICS Model of Briarcliff Rd & North Druid Hills Rd
Figure 138. Screen Capture. TEXAS Model of Briarcliff Rd & North Druid Hills Rd
Figure 139. Photo. GoogleTM Map View of Roswell Road & Abernathy Road
Figure 140. Screen Capture. VISSIM Model of Roswell Road & Abernathy Road
Figure 141. Screen Capture. AIMSUN Model of Roswell Road & Abernathy Road
Figure 142. Screen Capture. PARAMICS Model of Roswell Road & Abernathy Road
Figure 143. Screen Capture. TEXAS Model of Roswell Road & Abernathy Road
Figure 144. Photo. GoogleTM Map View of Lafayette Ave & Fulton Street
Figure 145. Screen Capture. VISSIM Model of Lafayette Ave & Fulton Street
Figure 146. Screen Capture. AIMSUN Model of Lafayette Ave & Fulton Street
Figure 147. Screen Capture. PARAMICS Model of Lafayette Ave & Fulton Street
Figure 148. Screen Capture. TEXAS Model of Lafayette Ave & Fulton Street
Figure 149. Photo. GoogleTM Map View of Ryan Ave & Davison Ave
Figure 150. Screen Capture. VISSIM Model of Ryan Ave & Davison Ave
Figure 151. Screen Capture. AIMSUN Model of Ryan Ave & Davison Ave
Figure 152. Screen Capture. PARAMICS Model of Ryan Ave & Davison Ave
Figure 153. Screen Capture. TEXAS Model of Ryan Ave & Davison Ave
Figure 154. Photo. GoogleTM Map View of Howe Ave & Fair Oaks Boulevard
Figure 155. Screen Capture. VISSIM Model of Howe Ave & Fair Oaks Boulevard
Figure 156. Screen Capture. AIMSUN Model of Howe Ave & Fair Oaks Boulevard
Figure 157. Screen Capture. PARAMICS Model of Howe Ave & Fair Oaks Boulevard
Figure 158. Screen Capture. TEXAS Model of Howe Ave & Fair Oaks Boulevard
Figure 159. Graph. Conflicts Number C-N2 Comparison for Intersection 1 at AM Peak
Figure 160. Graph. Conflicts Number C-N3 Comparison for Intersection 1 at AM Peak
Figure 161. Graph. Conflicts Number C-N2 Comparison for Intersection 1 at Mid Peak
Figure 162. Graph. Conflicts Number C-N3 Comparison for Intersection 1 at Mid Peak
Figure 163. Graph. Conflicts Number C-N2 Comparison for Intersection 1 at PM Peak
Figure 164. Graph. Conflicts Number C-N3 Comparison for Intersection 1 at PM Peak
Figure 165. Graph. Conflicts Number C-N2 Comparison for Intersection 2 at AM Peak
Figure 166. Graph. Conflicts Number C-N3 Comparison for Intersection 2 at AM Peak
Figure 167. Graph. Conflicts Number C-N2 Comparison for Intersection 2 at Mid Peak
Figure 168. Graph. Conflicts Number C-N3 Comparison for Intersection 2 at Mid Peak
Figure 169. Graph. Conflicts Number C-N2 Comparison for Intersection 2 at PM Peak
Figure 170. Graph. Conflicts Number C-N3 Comparison for Intersection 2 at PM Peak
Figure 171. Graph. Conflicts Number C-N2 Comparison for Intersection 3 at AM Peak
Figure 172. Graph. Conflicts Number C-N3 Comparison for Intersection 3 at AM Peak
Figure 173. Graph. Conflicts Number C-N2 Comparison for Intersection 3 at PM Peak
Figure 174. Graph. Conflicts Number C-N3 Comparison for Intersection 3 at PM Peak
Figure 175. Graph. Conflicts Number C-N2 Comparison for Intersection 4 at AM Peak
Figure 176. Graph. Conflicts Number C-N3 Comparison for Intersection 4 at AM Peak
Figure 177. Graph. Conflicts Number C-N2 Comparison for Intersection 4 at PM Peak
Figure 178. Graph. Conflicts Number C-N3 Comparison for Intersection 4 at PM Peak
Figure 179. Graph. Conflicts Number C-N2 Comparison for Intersection 5 at AM Peak
Figure 180. Graph. Conflicts Number C-N3 Comparison for Intersection 5 at AM Peak
Figure 181. Graph. Conflicts Number C-N2 Comparison for Intersection 5 at PM Peak
Figure 182. Graph. Conflicts Number C-N3 Comparison for Intersection 5 at PM Peak
Figure 183. Screen Capture. VISSIM Conflict Layout for AM Peak Hour of Intersection 1 (Total 85)
Figure 184. Screen Capture. AIMSUN Conflict Layout for AM Peak Hour of Intersection 1 (Total 271)
Figure 185. Screen Capture. PARAMICS Conflict Layout for AM Peak Hour of Intersection 1 (Total 427)
Figure 186. Screen Capture. TEXAS Conflict Layout for AM Peak Hour of Intersection 1 (Total 2,178)
Figure 187. Screen Capture. VISSIM Conflict Layout for Mid Peak Hour of Intersection 1 (Total 84)
Figure 188. Screen Capture. AIMSUN Conflict Layout for Mid Peak Hour of Intersection 1 (Total 222)
Figure 189. Screen Capture. PARAMICS Conflict Layout for Mid Peak Hour of Intersection 1 (Total 209)
Figure 190. Screen Capture. TEXAS Conflict Layout for Mid Peak Hour of Intersection 1 (Total 1,359)
Figure 191. Screen Capture. VISSIM Conflict Layout for PM Peak Hour of Intersection 1 (Total 47
Figure 192. Screen Capture. AIMSUN Conflict Layout for PM Peak Hour of Intersection 1 (Total 156)
Figure 193. Screen Capture. PARAMICS Conflict Layout for PM Peak Hour of Intersection 1 (Total 118)
Figure 194. Screen Capture. TEXAS Conflict Layout for PM Peak Hour of Intersection 1 (Total 878)
Figure 195. Screen Capture. VISSIM Conflict Layout for AM Peak Hour of Intersection 2 (Total 181)
Figure 196. Screen Capture. AIMSUN Conflict Layout for AM Peak Hour of Intersection 2 (Total 997)
Figure 197. Screen Capture. PARAMICS Conflict Layout for AM Peak Hour of Intersection 2 (Total 565)
Figure 198. Screen Capture. TEXAS Conflict Layout for AM Peak Hour of Intersection 2 (Total 2,242)
Figure 199. Screen Capture. VISSIM Conflict Layout for Mid Peak Hour of Intersection 2 (Total 215)
Figure 200. Screen Capture. AIMSUN Conflict Layout for Mid Peak Hour of Intersection 2 (Total 1,107)
Figure 201. Screen Capture. PARAMICS Conflict Layout for Mid Peak Hour of Intersection 2 (Total 708)
Figure 202. Screen Capture. TEXAS Conflict Layout for Mid Peak Hour of Intersection 2 (Total 5,173)
Figure 203. Screen Capture. VISSIM Conflict Layout for PM Peak Hour of Intersection 2 (Total 214)
Figure 204. Screen Capture. AIMSUN Conflict Layout for PM Peak Hour of Intersection 2 (Total 619)
Figure 205. Screen Capture. PARAMICS Conflict Layout for PM Peak Hour of Intersection 2 (Total 485)
Figure 206. Screen Capture. TEXAS Conflict Layout for PM Peak Hour of Intersection 2 (Total 4,652
Figure 207. Screen Capture. VISSIM Conflict Layout for AM Peak Hour of Intersection 3 (Total 59)
Figure 208. Screen Capture. AIMSUN Conflict Layout for AM Peak Hour of Intersection 3 (Total 128)
Figure 209. Screen Capture. PARAMICS Conflict Layout for AM Peak Hour of Intersection 3 (Total 46)
Figure 210. Screen Capture. TEXAS Conflict Layout for AM Peak Hour of 7,500B (Total 138)
Figure 211. Screen Capture. VISSIM Conflict Layout for PM Peak Hour of Intersection 3 (Total 93)
Figure 212. Screen Capture. AIMSUN Conflict Layout for PM Peak Hour of Intersection 3 (Total 184)
Figure 213. Screen Capture. PARAMICS Conflict Layout for PM Peak Hour of Intersection 3 (Total 45)
Figure 214. Screen Capture. TEXAS Conflict Layout for PM Peak Hour of Intersection 3 (Total 182)
Figure 215. Screen Capture. VISSIM Conflict Layout for AM Peak Hour of Intersection 4 (Total 78)
Figure 216. Screen Capture. AIMSUN Conflict Layout for AM Peak Hour of Intersection 4 (Total 143)
Figure 217. Screen Capture. PARAMICS Conflict Layout for AM Peak Hour of Intersection 4 (Total 45)
Figure 218. Screen Capture. TEXAS Conflict Layout for AM Peak Hour of Intersection 4 (Total 206)
Figure 219. Screen Capture. VISSIM Conflict Layout for PM Peak Hour of Intersection 4 (Total 104)
Figure 220. Screen Capture. AIMSUN Conflict Layout for PM Peak Hour of Intersection 4 (Total 229)
Figure 221. Screen Capture. PARAMICS Conflict Layout for PM Peak Hour of Intersection 4 (Total 111
Figure 222. Screen Capture. TEXAS Conflict Layout for PM Peak Hour of Intersection 4 (Total 379)
Figure 223. Screen Capture. VISSIM Conflict Layout for AM Peak Hour of Intersection 5 (Total 185)
Figure 224. Screen Capture. AIMSUN Conflict Layout for AM Peak Hour of Intersection 5 (Total 558)
Figure 225. Screen Capture. PARAMICS Conflict Layout for AM Peak Hour of Intersection 5 (Total 352)
Figure 226. Screen Capture. TEXAS Conflict Layout for AM Peak Hour of Intersection 5 (Total 1,972)
Figure 227. Screen Capture. VISSIM Conflict Layout for PM Peak Hour of Intersection 5 (Total 301)
Figure 228. Screen Capture. AIMSUN Conflict Layout for PM Peak Hour of Intersection 5 (Total 988)
Figure 229. Screen Capture. PARAMICS Conflict Layout for PM Peak Hour of Intersection 5 (Total 389)
Figure 230. Screen Capture. TEXAS Conflict Layout for PM Peak Hour of Intersection 5 (Total 4,349)
Figure 231. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 1 at AM Peak
Figure 232. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 1 at Mid Peak
Figure 233. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 1 at PM Peak
Figure 234. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 2 at AM Peak
Figure 235. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 2 at Mid Peak
Figure 236. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 2 at PM Peak
Figure 237. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 3 at AM Peak
Figure 238. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 3 at PM Peak
Figure 239. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 4 at AM Peak
Figure 240. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 4 at PM Peak
Figure 241. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 5 at AM Peak
Figure 242. Graph. 3-D View of the Comparison on Major Surrogate Safety Measures for Intersection 5 at PM Peak
Figure 243. Screen Capture. First and Second Vehicles Arriving
Figure 244. Screen Capture. First Vehicle Stops and Second Vehicle Decides to Change Lanes
Figure 245. Screen Capture. Second Vehicle Changes Lanes and Stops
Figure 246. Screen Capture. Third Vehicle Arriving
Figure 247. Screen Capture. Third Vehicle Crashing into Second Vehicle

LIST OF TABLES

Table 1. Conflict Events Data for Each Replication
Table 2. Mean Safety Measures for Each Conflict Type
Table 3. Example of T-Test Results for Number of Conflict Events
Table 4. Example of T-Test Results for Average TTC Value
Table 5. Example of Rank Order Data Sets
Table 6. Example for the Spearman Rank Correlation Calculation
Table 7. Typical K-Factors
Table 8. Case 1 Service Flow by Each Approach
Table 9. Case 1 Comparison Results for Total Conflicts
Table 10. Case 1 Comparison Results for Only Crossing Conflicts
Table 11. Case 1 Comparison Results for Rear-End Conflicts
Table 12. Case 1 Comparison Results for Lane Change Conflicts
Table 13. Case 1 Comparison Results for Average Surrogate Measures of Safety
Table 14. Case 1 Spearman Rank Correlations Between Conflicts and Crash Frequency
Table 15. Case 2 Service Flow by Each Approach
Table 16. Case 2 Comparison Results for Total Conflicts
Table 17. Case 2 Comparison Results for Crossing Conflicts
Table 18. Case 2 Comparison Results for Rear-End Conflicts
Table 19. Case 2 Comparison Results for Lane-Change Conflicts
Table 20. Case 2 Comparison Results for Average Surrogate Measures of Safety
Table 21. Case 2 Spearman Rank Correlations Between Conflicts and Crash Frequency
Table 22. Case 3 Service Flow by Each Approach
Table 23. Case 3 Comparison Results for Total Conflicts
Table 24. Case 3 Comparison Results for Crossing Conflicts
Table 25. Case 3 Comparison Results for Rear-End Conflicts
Table 26. Case 3 Comparison Results for Lane-Change Conflicts
Table 27. Case 3 Comparison Results for Average Surrogate Measures of Safety
Table 28. Case 3 Spearman Rank Correlations Between Conflicts and Crash Frequency
Table 29. Case 4 Service Flow by Each Approach
Table 30. Case 4 Comparison Results for All Conflict Event Types
Table 31. Case 4 Comparison Results for Rear-End Conflicts
Table 32. Case 4 Comparison Results for Lane-Change Conflicts
Table 33. Case 4 Comparison Results for Average Surrogate Measures of Safety
Table 34. Case 4 Spearman Rank Correlations Between Conflicts and Crash Frequency
Table 35. Case 5 Service Flow by Each Approach
Table 36. Case 5 Comparison Results for Total Conflicts
Table 37. Case 5 Comparison Results for Rear-End Conflicts
Table 38. Case 5 Comparison Results for Lane-Change Conflicts
Table 39. Case 5 Comparison Results for Average Surrogate Measures of Safety
Table 40. Case 5 Spearman Rank Correlations Between Conflicts and Crash Frequency
Table 41. Case 6 Service Flow by Each Approach
Table 42. Case 6 Comparison Results for Total Conflicts
Table 43. Case 6 Comparison Results for Rear-End Conflicts
Table 44. Case 6 Comparison Results for Lane Change Conflicts
Table 45. Case 6 Comparison Results for Average Surrogate Measures of Safety
Table 46. Case 6 Spearman Rank Correlations Between Conflicts and Crash Frequency
Table 47. Case 7 Service Flow by Each Approach
Table 48. Case 7 Comparison Results for Total Conflicts
Table 49. Case 7 Comparison Results for Rear-End Conflicts
Table 50. Case 7 Comparison Results for Lane-Change Conflicts
Table 51. Case 7 Comparison Results for Average Surrogate Measures of Safety
Table 52. Case 7 Spearman Rank Correlations Between Conflicts and Crash Frequency
Table 53. Case 8 Service Flow by Each Approach
Table 54. Case 8 Comparison Results for Total Conflicts
Table 55. Case 8 Comparison Results for Crossing Conflicts
Table 56. Case 8 Comparison Results for Rear-End Conflicts
Table 57. Case 8 Comparison Results for Lane-Change Conflicts
Table 58. Case 8 Comparison Results for Average Surrogate Measures of Safety
Table 59. Case 9 Service Flow by Each Approach
Table 60. Case 10 Service Flow by Each Approach
Table 61. Case 9 Comparison Results for Total Conflicts
Table 62. Case 9 Comparison Results for Crossing Conflicts
Table 63. Case 9 Comparison Results for Rear-End Conflicts
Table 64. Case 9 Comparison Results for Lane Change Conflicts
Table 65. Case 9 Comparison Results for Average Surrogate Measures of Safety
Table 66. Case 10 Comparison Results for Total Conflicts
Table 67. Case 10 Comparison Results for Crossing Conflicts
Table 68. Case 10 Comparison Results for Rear-End Conflicts
Table 69. Case 10 Comparison Results for Lane-Change Conflicts
Table 70. Case 10 Comparison Results for Average Surrogate Measures of Safety
Table 71. Case 9 Spearman Rank Correlations Between Conflicts and Crash Frequency
Table 72. Case 11 Service Flow by Each Approach
Table 73. Case 11 Comparison Results for Total Conflicts
Table 74. Case 11 Comparison Results for Crossing Conflicts
Table 75. Case 11 Comparison Results for Rear-End Conflicts
Table 76. Case 11 Comparison Results for Lane Change Conflicts
Table 77. Case 11 Comparison Results for Average Surrogate Measures of Safety
Table 78. Summary of Theoretical Validation Case Studies
Table 79. Summary of Conflict Rates by Test Case (Conflicts/100 Entering Vehicles)
Table 80. Summary of Removed Crash and Low-Speed Event Data
Table 81. Distribution of Conflicts and Crashes by Incident Type
Table 82. Prediction Model for Crashes as a Function of Major and Minor ADT
Table 83. Nonlinear Regression Model for Crashes as a Function of Conflicts
Table 84. Prediction Model for Total Conflicts as a Function of Volume
Table 85. Prediction Models for Crossing Conflicts Based on Traffic Volume
Table 86. Prediction Model for Rear-End Crashes Based on Traffic Volume
Table 87. Number and Type of Conflicts Based on Different Modeling Schemes
Table 88. Number and Type of Conflicts Based on Gap Size
Table 89. Percentages of Locations Exhibiting a Decrease in the Number of Conflicts (Including Simulated Crashes)
Table 90. Percentages of Locations Exhibiting a Decrease in the Number of Conflicts (Excluding Simulated Crashes)
Table 91. Effect of Varying Lateral Clearance (Simulated Crashes Included)
Table 92. Effect of Varying Lateral Clearance (Simulated Crashes Excluded)
Table 93. Conflicts Number Under AM Peak-Hour Condition for Intersection 1
Table 94. Conflicts Number Under Mid Peak-Hour Condition for Intersection 1
Table 95. Conflicts Number Under PM Peak-Hour Condition for Intersection 1
Table 96. Conflicts Number Under AM Peak-Hour Condition for Intersection 2
Table 97. Conflicts Number Under Mid Peak-Hour Condition for Intersection 2
Table 98. Conflicts Number Under PM Peak-Hour Condition for Intersection 2
Table 99. Conflicts Number Under AM Peak-Hour Condition for Intersection 3
Table 100. Conflicts Number Under PM Peak-Hour Condition for Intersection 3
Table 101. Conflicts Number Under AM Peak-Hour Condition for Intersection 4
Table 102. Conflicts Number Under PM Peak-Hour Condition for Intersection 4
Table 103. Conflicts Number Under AM Peak-Hour Condition for Intersection 5
Table 104. Conflicts Number Under PM Peak-Hour Condition for Intersection 5
Table 105. Safety Measures Under AM Peak Hour for Intersection 1
Table 106. Safety Measures Under Mid Peak Hour for Intersection 1
Table 107. Safety Measures Under PM Peak Hour for Intersection 1
Table 108. Safety Measures Under AM Peak Hour for Intersection 2
Table 109. Safety Measures Under Mid Peak Hour for Intersection 2
Table 110. Safety Measures Under PM Peak Hour for Intersection 2
Table 111. Safety Measures Under AM Peak Hour for Intersection 3
Table 112. Safety Measures Under PM Peak Hour for Intersection 3
Table 113. Safety Measures under AM Peak Hour for Intersection 4
Table 114. Safety Measures Under PM Peak Hour for Intersection 4
Table 115. Safety Measures Under AM Peak Hour for Intersection 5
Table 116. Safety Measures Under PM Peak Hour for Intersection 5
Table 117. MOEs for Intersection 1
Table 118. MOEs for Intersection 2
Table 119. MOEs for Intersection 3
Table 120. MOEs for Intersection 4
Table 121. MOEs for Intersection 5
Table 122. Canadian Intersections Geometry and Traffic Flow Data
Table 123. Average Yearly Crashes per Intersection
Table 124. Average Hourly Conflicts per Intersection
Table 125. Average Hourly Conflicts per Intersection
Table 126. Gap Sizes of 4, 5, and 6 Seconds and Their Corresponding Conflict Counts

LIST OF ACRONYMS AND SYMBOLS

Acronym Definition

AADT
annual average daily traffic
ADT
average daily traffic
AMF
accident modification factor
CSV
comma separated values
EB
Empirical Bayes
FHWA
Federal Highway Administration
GUI
graphical user interface
ICBC
Insurance Corporation of British Columbia
PET
post-encroachment time
SPUI
Single-Point Urban Interchange
SSAM
Surrogate Safety Assessment Model
TRJ
The filename extension for vehicle trajectory files.
TTC
time to collision

Symbol Definition

α Greek letter Alpha

β Greek letter Beta

Δ Greek letter Delta

λ Greek letter Lamda

π Greek letter Pi

θ Greek letter Theta

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ResearchFHWA
FHWA
United States Department of Transportation - Federal Highway Administration