Minimum Sign Retroreflectivity Requirements

Highway statistics reveal a nighttime accident rate that is more than three times the daytime rate. While factors such as intoxication and fatigue are partly responsible for this disparity, reduced visibility also plays a major role. In this study, FHWA developed a model that would predict needed retroreflectivity on a case-by-case basis, considering all critical determining factors, and proposed minimum sign retroreflectivity guideline values. These values were further evaluated by a laboratory study and a field evaluation. The final minimum sign retroreflective values were submited to FHWA’s Office of Highway Safety for rule making.