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.
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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 |