Turner-Fairbank Highway Research Center

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The Application of an Improved Accident Analysis Method for Highway Safety Evaluations

Product Type

HSIS Summary Report


Jun Wang




This study was undertaken to apply the Empirical Bayes Estimation of Safety and Transportation (EBEST) methodology to actual HSIS data from Minnesota. Both EBEST and the "classical" before/after methodologies were used. A treatment group of 13 intersections where new traffic signals were installed and a reference group of 79 intersections were selected. After traffic signals were installed, the total number of crashes decreased 25 percent by the EBEST method and 30 percent by the classical method. Injury crashes decreased 23 percent by the EBEST method and 38 percent by the classical method. Thus, the classical method overestimated the treatment effect. More generally, a simple before-and-after comparison at a site where a safety treatment is selected based on its crash experience is likely to result in an overestimation of the treatments effect, because regression-to-the-mean is not accounted for.

Link To HSIS Summary Report

The Application of an Improved Accident Analysis Method for Highway Safety Evaluations


Crash analysis method
Treatment effect
Regression to the mean

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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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Technical Summaries

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

In addition to conducting research, HSIS resources are also used to develop products that can be used by practitioners in the analysis of safety problems.

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Other Projects

HSIS data are sometimes used in research studies that result in other types of finished products, such as dissertations, theses, and conference proceedings.

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