Sign Life Expectancy on Low-Volume Roads in Iowa

Traffic signs provide warning and guidance information to drivers 24 h a day. They also represent a significant maintenance and replacement concern and cost for agencies with the advent of retroreflectivity requirements. In some cases, agencies choose to replace their signs in conjunction with the end of the manufacturer warranty period or other time intervals to maintain sign retroreflectivity. However, this could result in signs being replaced while they still exceed their minimum retroreflectivity requirements, with labor and material costs being incurred years before necessary. This research evaluated retroreflectivity data from in-service signs in Iowa, U.S., to determine expected sign life values. It evaluated 10,799 retroreflectivity data points across three different sheeting materials for a variety of sign types. A total of 65 linear regression models were developed to evaluate signs by sheeting type, age, and sign category (regulatory, warning, and guide), as well as directional orientation. The results indicated that all sheeting materials, sign types, and sign directions were predicted to have lives of at least 10 years before falling below Manual on Uniform Traffic Control Devices (MUTCD) minimums. Plots of retroreflectivity versus age indicated that many signs remained well above the MUTCD minimums at the predicted age where failure was expected. In general, the predicted lives for a material/sign type/direction combination were greater than 5 years longer than manufacturer warranty periods. For conservative purposes, agencies could consider a sign to be approaching minimum retroreflectivity levels at approximately 5 years past the manufacturer warranty, based on the research results.