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Publication Number: FHWA-RD-03-050

Surrogate Safety Measures From Traffic Simulation Models

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Technical Report Documentation Page

1. Report No.


2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

Surrogate Safety Measures From Traffic Simulation Models, Final Report

5. Report Date

6. Performing Organization Code

7. Author(s)

Douglas Gettman and Larry Head

8. Performing Organization Report No.

9. Performing Organization Name and Address

Siemens Gardner Transportation Systems

6375 E. Tanque Verde, Suite 170

Tucson, AZ 85715

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

Office of Safety Research and Development

Turner-Fairbank Highway Research Center

Federal Highway Administration

6300 Georgetown Pike

McLean, VA 22101

13. Type of Report and Period Covered

Final Report

October 2001 – January 2003

14. Sponsoring Agency Code

15. Supplementary Notes

FHWA Contracting Officer’s Technical Representative (COTR): Joe Bared, Office of Safety R&D

16. Abstract

This project investigates the potential for deriving surrogate measures of safety from existing microscopic traffic simulation models for intersections. The process of computing the measures in the simulation, extracting the required data, and summarizing the results is denoted as the Surrogate Safety Assessment Methodology. These surrogate measures could then be used to support traffic engineering alternatives evaluation with respect to safety for both signalized and unsignalized intersections. The report describes the five main activities of this project: (1) review of previous work in modeling of safety at traffic facilities (focusing on intersection safety modeling) using surrogate measures, (2) survey of the capabilities of existing traffic simulation models to support derivation of surrogate measures of safety, (3) identification of use cases and functional requirements for a surrogate safety assessment tool that interacts with traffic simulation model outputs, (4) specification of algorithms for calculating surrogate measures of safety appropriate for intersections, and (5) suggestions for validation activities to support the analysis potential for surrogate measures and compare surrogate measures from simulation models with field data and previous safety studies.

17. Key Words

Surrogate safety measures, traffic simulation models, traffic conflicts, intersection safety assessment.

18. Distribution Statement

No restrictions.  This document is available to the public through the National Technical Information Service.  Springfield, VA 22161

19. Security Classif. (of this report)


20. Security Classif. (of this page)


21. No. of Pages


22. Price

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

SI* (Modern Metric) Conversion Factors


This report summarizes the activities and results of a project to evaluate the assessment of surrogate measures of safety for traffic intersections from existing, commercially available traffic simulation models. The objective of the project was to evaluate the various simulation models’ capabilities for producing measures of intersection safety and specify algorithms for calculating the measures.

Copies of this report can be obtained from the Research and Technology Report Center, 9701 Philadelphia Court, Unit Q, Lanham, Maryland 20706; telephone: (301) 577-0818; fax: (301) 577-1421; or the National Technical Information Service (NTIS), 5285 Port Royal Road, Springfield, Virginia 22161; telephone: (703) 487-4650; fax: (703) 321-8547.

Michael F. Trentacoste


Office of Safety

Research and Development


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.


  1. Introduction

  2. Literature Review


      Conflict Severity  Ranking Conflict Measures on Collection Desirability

    Other Surrogate Measures

    Surrogate Measures From Microscopic Simulations   General-Purpose Microscopic Models

    Literature Summary

  3. Traffic Simulation Model Overview

  4. Discussion of Microscopic Simulation Model Comparisons

  5. Summary of Simulation Model Features Review

  6. SSAM Functional Requirements

    Functional Requirements Development Process

      System Owner, Users, and Stakeholders

      SSAM Objectives

      Concept of Operation of the SSAM

    Use Case Analysis

      System Users

      Use Case Packages

    User Interface Mock-Ups

    Functional Requirements

  7. Algorithms for Surrogate Measures of Safety at Intersections

    Conflict Event Descriptions

      Crossing Flows—Conflict Point Events

      Merging Crossing Flows—Conflict Line Events

      Adjacent Flows—Lane-Changing Conflict Line Events

      Following Flows—Rear-End Conflict Line Events

      Collision Types Not Represented in the Surrogate Measures

      Pedestrian Collisions

      U-Turn-Related Collisions


      Unrepresented Evasive Maneuvers

      Significant Unrepresented Conflict Event Contributors

    Conflict Point

    Conflict Line

    Rear-End Conflict Line

    Summary of Conflict Points, Lines, and Rear-End Lines

    Surrogate Measures Definitions

      Severity of Conflict and Severity of Resulting Collision

    Surrogate Measures for Conflict Points

    Time To Collision

      Post-Encroachment Time



      Initial Deceleration Rate

      Location of the Conflict Point

    Computational Algorithms—Conflict Points

    Surrogate Measures for Conflict Lines With Merging Flows

      Time To Collision

      Post-Encroachment Time



      Initial Deceleration Rate

      Location of the Conflict Line

    Computational Algorithms—Conflict Lines for Merging Flows

    Surrogate Measures for Rear-End Conflict Lines

      Time To Collision

      Post-Encroachment Time



      Initial Deceleration Rate

      Location of the Conflict Line

    Computational Algorithms—Rear-End Conflict Lines


  8. Event File Specification

    Elements in the Event File

      Elements in the Header

      Elements in Each Time Step

      Implications of File Size

      File Naming Conventions

  9. Validation of Surrogate Measures

  10. Report Summary

  11. References



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