Turner-Fairbank Highway Research Center

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Interchange Safety Analysis Tool (ISAT): User Manual

Product Type

Research Report


Torbic, D.J., D.W. Harwood, D.K. Gilmore, and K.R. Richard




This User Manual describes the usage and operation of the spreadsheet-based Interchange Safety Analysis Tool (ISAT). ISAT provides design and safety engineers with an automated tool for assessing the safety effects of geometric design and traffic control features at an 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 (i.e., mainline freeway segments, ramps, ramp terminals and intersections, and crossroad roadway segments), the number of predicted crashes by year, and the number of predicted crashes by collision type. This User Manual presents basic information for getting started with using ISAT, the general methodology that users will follow when conducting an analysis with ISAT, input requirements of the program, default data incorporated within the program and recommendations on when and how these default data should be updated by the user, output reports generated by ISAT, and general information on different applications for which ISAT can be applied. An example problem is also provided on the safety performance of a rural diamond interchange and surrounding roadway network, illustrating user inputs and generated output reports.

Link To Research Report

Interchange Safety Analysis Tool (ISAT): User Manual


geometric design
safety performance function

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HSIS Summaries

HSIS Summary Reports are two to eight pages in length and include a brief description of the issue addressed, data used, methodology applied, significant results, and practical implications.

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Research Reports

A variety of research studies have been performed using data from HSIS. Many of the final reports prepared are now available electronically.

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Research reports are often summarized in executive summaries, technical briefs, or other abbreviated formats. Included here are those road safety summaries that involved research using HSIS data.

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Safety Analysis Tools

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