Keith Knappkknapp@iastate.edu email >
Director, Iowa LTAP
About the research
Speed feedback signs are used in a variety of situations and settings including work zones, school zones, and along residential or commercial locations. Their impacts have generally been shown to be a low to moderate reduction in speeds.
This project investigated the need for and potential use of a speed feedback sign loan program by local agencies, including the type of signs to acquire and loan to local agencies, and the impacts of use on vehicle speeds before and after activation of the digital display board on the signs. Two Traffic Logix SafePace 475 speed feedback signs were purchased for the project and incorporated into the Iowa Local Technical Assistance Program Equipment Loan Program, allowing agencies to become familiar with the use and operation of such equipment when seeking to determine if a purchase should be made. During the project, the researchers received loan requests from four agencies to deploy the trailer-based sign at eight sites. To complete the loans, the researchers programmed the sign based on existing speed limits, delivered and set up the sign, and retrieved the sign and downloaded the measured speed data for analysis.
The use of this sign provided both useful speed data for analysis and experience in working with the setup and operation of the signs in the field for future consideration by the loan program. In analyzing the speed data, the sign deployments were largely successful from the perspective of having an impact on driver behaviors. Mean speeds were reduced at six of the eight deployment sites, while 85th percentile speeds were reduced at all eight sites. Statistical evaluations found that all mean speed reductions were statistically significant. The percentages of drivers exceeding the posted speed limit by more than 15 mph were reduced at seven of eight sites. The extent of speed reductions at each site varied, and mean speed reductions were typically small (i.e., less than 1 mph), while 85th percentile reductions did not exceed 3 mph. Still, these results point toward the signs capturing driver attention over the short term. Agencies can expect similar impacts for short-term deployments along similar roadways.