Dynamic Speed Feedback Signs Are Effective in Reducing Driver Speeds: A Meta-Analysis

Abstract

Excess speed contributes to over a quarter of all fatal automobile crashes in the United States, costing society billions of dollars each year. Lowering excess speeds to reduce these human, societal, and economic costs is therefore a major focus of safety officials and highway engineers. This study presents a quantitative review of the effectiveness of dynamic speed feedback signs (DSFS), which provide drivers with real-time feedback on their speed so that drivers traveling above the posted speed can slow appropriately. Using a meta-analysis of 43 publications, this study demonstrates that DSFS can effectively reduce speeds in different contexts (e.g., school and work zones) and for different vehicle types (e.g., heavy and light duty). Across all types of contexts and vehicle types that were analyzed, the meta-analysis identified statistically significant reductions in speeds when DSFS are installed. Overall, reductions of 4 mph were detected as a result of DSFS installation for passenger cars, and reductions between 2 and 4 mph were detected across vehicle types in the different contexts assessed. As reductions in speed of just 4 mph of vehicles traveling 30–35 mph can reduce fatal pedestrian-vehicle strikes by upwards of 40%, these findings demonstrate that the reductions in speed at DSFS were not only statistically significant, but also practically significant in areas such as school zones and work zones.