Turner-Fairbank Highway Research Center

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Development of Severity Indices for Roadside Objects: Resource Materials

Product Type

Research Report


Forrest M. Council and J. Richard Stewart




This study was an attempt to develop severity indices (SIs) for various fixed objects that are impacted when vehicles leave the roadway. The objectives of the study were two-fold, including both the development of new indices with recent data from two states and the exploration of methodological issues related to statistical modeling and a literature-based exploration of unreported crashes. Both a severe injury SI and a cost-based SI were developed for a wide range of crash situations using data from both North Carolina and Illinois, where injury could be more precisely linked to the specific object struck. While the final SI indices developed were not categorized by exactly the same control variables for the two states, the values of the indices were, in general, moderately consistent between the states. Findings from North Carolina and Illinois were also consistent to a significant degree with SIs developed earlier by Mak, et al., using Texas data. In the limited sample of airbag-related impacts with guardrails, trees, and utility poles, it appears that the airbag will significantly reduce the value of the SI, and that the reduction could range from 30 to 70%. Additional future research is needed on the effects on SIs of both airbags and unreported crashes.

Link To Research Report

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Severity indices
Fixed objects
Crash severity

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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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