Safety Impacts and Other Implications of Raised Speed Limits on High-Speed Roads (2006) / Chapter Skim
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Research Results Digest 303 April 2006 SUMMARY This report describes the analyses performed and results obtained by a study of safety and other impacts of speed limit changes on high-speed roads. The information will be valuable for researchers studying the complex relationship between safety and vehicle speeds.
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limit. This data distinction is expected to translate into overestimates of the magnitude of the injury severity distribution changes following a speed limit change.
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• What are the systemwide effects when a speed limit is changed on a particular roadsegment, apart from the safety implications on those segments themselves? Are there significant implications for safety on other roadways?
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SAFETY IMPACTS OF SPEED LIMIT CHANGES The safety-related analyses were based on a comprehensive framework of the disaggregate relationships among speed limits, driver speed choices, crash occurrences, and crash severities. The analyses drew on various data types, including loop detector measurements; stated preference surveys and revealed choices; and crash records containing information about crash counts and severities, vehicles and their occupants, and roadways and their environments.
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Crash Occurrence Models The results of the project analyses of the statistical association between speed limits and total crash rates suggested only slight effects. The project's main work on crash occurrence models was based on datasets obtained by clustering Highway Safety Information System (HSIS)
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In the higher speed limit range (65 to 75 mph) , on the other hand, the increase in the total number of crashes is considerably smaller (0.64%)
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NON-SAFETY IMPACTS OF SPEED LIMIT CHANGES The investigation of non-safety impacts of speed limit changes relied on published literature, unpublished reports by state DOTs, and results of surveys of state DOT and police officials. This investigation was a lower-priority project effort than the analysis of safety impacts discussed above.
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DATA RECOMMENDATIONS The methods used in this work were guided, and limited, by the extent and quality of existing datasets. For example, Washington State's HSIS dataset is thought to be the best that the United States offers, but its panel datasets are missing key years (1997 and 1998)
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quently preserved and stored; indeed, the ongoing federally sponsored Archived Data User Service (ADUS) represents a national significant effort to standardize and make available traffic and operations data from traffic sensor systems and other ITS components around the country.
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injuries is associated with higher speed limits. For this particular 10 mph speed limit change, a 24% increase in the fatal injury probability would be expected.
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Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP)
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