Safety Evaluation of Increasing Retroreflectivity of STOP Signs

This article reports on a study the evaluated the safety of retroreflectivity of stop signs. The authors define retroreflectivity as the property of a material that reflects a large portion of the light directly back to the source, through a wide range of angles of incidence of illumination. On a stop sign, retroreflective sheeting will redirect light from the driver's headlight back to the driver's eyes. The authors then describe their research study, which examined the change in crash frequency due to increasing the retroreflectivity of stop signs at unsignalized intersections. The nighttime study include 60 subjects of varying ages. The measure of effectiveness was legibility distance. The study included crash data from two states, Connecticut and South Carolina, which had implemented strategies to change to stop signs with higher reflectivity. Data analysis indicates that higher retroreflective stop signs may affect the likelihood of crashes at unsignalized intersections, but the effect is not detectable with the study design and available sample size. The exception is for rear-end crashes in South Carolina, where there was a significant reduction noted. Statistically significant reductions in crashes were found for some types of intersections. The authors stress that, given the low cost of implementing retroreflective stop signs, only a very modest reduction in crashes is needed to justify their use.