Traffic Sign Life Expectancy

Highway agencies with an inventory of traffic signs must adopt a method of maintaining those signs so that the retroreflectivity exceeds established thresholds. Understanding expected sign life can help agencies phase sign replacements over a number of years in order to manage maintenance costs. The primary goal of this research is to provide objective data about sign life based on the degradation of retroreflectivity and color over time. A literature review found sign retroreflectivity research around the country, however, none of the studies are conclusive. Eight Minnesota agencies took retroreflectometer readings on in-place signs across the state. Disaggregated measurements by sheeting material and color did not leave a large enough sample for conclusive results, and very few signs fell below minimum retroreflectivity thresholds. Data suggests sign life exceeds the manufacturer's warranty and that a controlled environment with known conditions will produce more reliable data. MnDOT established a test deck at MnROAD to take multiple retroreflectivity and color readings over time to the point of failure in a controlled environment. The best information inferred from the results is an estimate for an expected sign life of 12 to 20 years for beaded sheeting and 15 to 30 years for prismatic sheeting. Agencies are encouraged to move forward and adopt a sign maintenance method and expected sign life by bringing sign management decisions under an umbrella of immunity. This document has suggested best policy practices and statements for sign maintenance and management assembled by a panel including engineers and risk management specialists.