Updating Safety Performance Functions for Data-Driven Safety Analysis

Data-driven safety analysis (DDSA) methods, including those presented in the AASHTO Highway Safety Manual (HSM), are becoming increasingly popular due to their ability to reliably and quantitatively assess the safety performance of existing and proposed roadways. Predictive safety analysis methods are implemented using the following types of statistical models: (1) Safety performance functions (SPFs), which predict the crash frequency for a given set of geometric and operational conditions. SPFs can be simple (i.e., AADT-only models) for planning purposes or detailed (i.e., many input variables). (2) Severity distribution functions (SDFs), which predict the severity distribution of crashes. (3) Crash modification factors (CMFs), which predict the effectiveness of safety treatments. Many SPFs and CMFs used in current tools were developed over the last 30 years as research created content for the HSM. For example, AASHTOWare Safety Analyst SPFs were developed using 1993-2001 data collected from the Highway Safety Information System (HSIS). Over time, the relationships represented by the models change due to improvements in vehicle design, changes in driver behavior, new legislation, and other trends. Millions of dollars have been allocated to research that develops these statistical models, and nearly as much funding is required to update models using current model development practices. New research is needed to determine how best to regularly update outdated models in the HSM, AASHTOWare Safety Analyst, and Interactive Highway Safety Design Model (IHSDM). There is an urgent need to examine the immense amount of resources needed to continue to develop and maintain the knowledge base to support the implementation of DDSA methods as well as to plan an efficient path forward for the future. The primary objective of this research is to plan for updates to SPFs, SDFs, and CMFs.


  • English


  • Status: Proposed
  • Funding: $500000
  • Contract Numbers:

    Project 17-93

  • Sponsor Organizations:

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Crichton-Sumners, Camille

  • Start Date: 20180619
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01672554
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 17-93
  • Files: TRB, RiP
  • Created Date: Jun 18 2018 3:03PM