The Current State of Research on the Long-Term Deterioration of Traffic Signs (TRB 130033)

The minimum retroreflectivity standard for traffic signs in the Manual on Uniform Traffic Control Devices requires that transportation agencies replace signs when they deteriorate beyond a prescribed minimum level of retroreflectivity. There are many sheeting products available with a variety of initial retroreflectivity levels for agencies to choose from when they need to install signs, but one primary concern agencies may have is their expected life. This paper serves as a compilation of studies related to the long-term deterioration of traffic signs to present what research has been completed in this area. The research compiled here shows that some signs may have an unrealistically long expected lifespan, a conclusion resulting from limitations in the study designs and their assumptions. A controlled long-term study of the deterioration of traffic signs with respect to retroreflectivity and color is encouraged to provide agencies the information necessary to select appropriate traffic sign products.