The application of continuous speed data for setting rational speed limits and improving roadway safety

Abstract

Speed is a primary contributor to crash frequencies and increased severity with over 30% of traffic fatalities attributed to speed. Research on rational speed limits suggests that simply lowering speed limits does not necessarily result in safer roadways; thus, there is a need to revisit the process by which speed limits, which are the front lines of any speed management program, are established. Traditionally, speed studies are conducted by taking spot speed observations at varying intervals along a roadway, however it would be ideal to have speed values continuously along a roadway. The specific objective of this research effort was to compare a continuous data collection method with existing methods and develop a methodology for integrating them to improve roadway safety. In this study, a group of drivers were equipped with a smartphone application which continuously captured video, vehicle speeds, and location data. The continuous speeds were then compared to speeds captured at eight fixed points. The results identified similarities in the 85th percentile speeds observed using the various data collection methods and a case study was conducted using FHWA’s expert system, USLimits2. The results provide evidence for a successful proof of concept for mapping continuous speed data to traditional speed data collection points that may help in the speed limit setting process as well as the establishment of appropriate advisory speed zones. This research endeavor outlined a methodology which may be utilized to improve the process by which engineers determine speed limits and advisory speed zones.