The objectives of this research were to (1) identify and describe factors that influence operating speed and (2) provide guidelines to make informed decisions related to establishing speed limits on roadways. The guidelines are to address the following: (a) an approach for determining the relationship between operating, design, posted and statutory speeds and how the differences among them impact safety performance; (b) identification and classification of nationwide data including, but not limited to, geometric design, access density, signal density, traffic volume characteristics, and enforcement practices that may impact operating speed; (c) an analysis of the 85th percentile speed and other statistical measures and factors as appropriate methods for setting speed limits; (d) implications of setting a speed limit lower than those recommended using the factors identified above. The focus of the research was on roadway functional classifications of minor arterials and higher as defined by AASHTO.
Status: Research is complete. The final report and associated deliverables are available at https://www.nap.edu/catalog/26216/posted-speed-limit-setting-procedure-and-tool-user-guide.