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Publication Number: FHWA-RD-97-084
Date: January 1997
Effects of Raising and Lowering Speed Limits on Selected Roadway Sections
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This report may be of interest to traffic engineers and policy makers responsible for making decisions involving the setting of speed limits on short segments on surface streets and highways in suburban and rural areas. The report results DO NOT involve changing speed limits on limited access highways (freeways). Measurements were also made on only four sections of Interstate highways and the results are presented in an appendix. The limited results of the freeway studies are an indication of the effects of raising the speed limit at the study sites only. Thus, use of the study findings should not be made in discussions about roadways that were formerly subject to the recently repealed National Maximum Speed Limit.
Because of the controversial nature of the subject of changing speed limits, and because the results are somewhat contrary to what many expect when speed limits are raised or lowered, the Transportation Research Board conducted a workshop at FHWA's request with this report as the primary resource paper. The purpose of the workshop was to get a thorough review of the methods of data collection and analyses to ensure that there are no questions as to the validity of the reported results. As recommended by the workshop participants, we are publishing this report with the few minor modifications identified. The changes dealt mostly with the following: removing the author's opinions that were not based on the research results, indicating why the initial experimental plan could not be followed, describing the three types of sites where speed limits were changed, doing an accident analysis based on accident rates to accommodate sites where traffic volumes had changed, and putting the freeway analysis in an appendix and noting that freeway data is much different than surface roadway site data in both speed changes and accident results. Also, the report title was changed to indicate that the sites studied were "selected roadway sections."