Intersection/Interchange Safety Analysis Tools

Interchange Safety Analysis Tool (ISAT)
ISAT provides design and safety engineers with an automated tool for assessing the safety effects of basic geometric design at typical existing interchange and adjacent roadway network. ISAT can also be used to predict the safety performance of design alternatives for new interchanges and prior to reconstruction of existing interchanges. The primary outputs from an analysis include: the number of predicted crashes for the entire interchange area, the number of predicted crashes by interchange element type, the number of predicted crashes by year, and the number of predicted crashes by collision type.

The ISAT user manual is available from The ISAT tool is available in Excel spreadsheet format. For more information contact Wei Zhang,, or Joe Bared,

Surrogate Safety Assessment Module (SSAM)
SSAM is a tool for traffic engineers to perform comparative safety analysis of highway design alternatives using traffic simulation models. The software combines traffic microsimulation and automated conflict analysis. It is designed to be compatible with as many traffic simulation models as possible, such as VISSIM, Paramics, AIMSUN, and TEXAS. SSAM uses the best possible surrogate measures (i.e., most representative of crash propensity) that are observable in simulation models. It also supports flexible analysis (e.g., different aggregations of statistics, different visualization types).

Additional SSAM documentation is available in two FHWA reports, which can be found at

  • Surrogate Safety Assessment Model and Validation: Final Report, FHWA-HRT-08-051.
  • Surrogate Safety Assessment Model (SSAM): Software User Manual, FHWA-HRT-08-050.

The SSAM software and open source code is available from Siemens Energy and Automation at

Program Contact

Robert Pollack


Karen Scurry


What’s New

NEW Guidance Memorandum on Fundamental Roadway and Traffic Data Elements to Improve the Highway Safety Improvement Program

NEW Background Report: Guidance for Roadway Safety Data to Support the Highway Safety Improvement Program

NEW Market Analysis of Collecting Fundamental Roadway Data Elements to Support the Highway Safety Improvement Program

MIRE Report, Ver. 1.0

A Guide to Developing Crash Modification Factors

The Highway Safety Manual (HSM)

Data and Analysis Tools


Crash Reduction Factors