About the research
Traffic signs provide warning and guidance information to drivers 24 hours a day. These signs 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 ensure that signs maintain their 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.
The research team evaluated retroreflectivity data from in-service signs in Iowa to determine expected sign life values for agencies. The researchers acquired sign retroreflectivity data from two Iowa counties and one city for analysis. The team utilized 10,799 retroreflectivity data points across three different sheeting materials for a variety of sign types. The researchers used linear regression to evaluate the two components of greatest interest to the research: the age of a sign versus its respective retroreflectivity value.
The researchers developed 65 linear regression models to evaluate signs by sheeting type and Federal Highway Administration (FHWA) Manual on Uniform Traffic Control Devices (MUTCD) category (regulatory and warning), as well as sign orientation (north, south, east, and west).
The results of the analysis indicated that all sheeting materials, sign types, and sign directions were predicted to have lives of at least 10 years before falling below MUTCD minimums. Plots of sign retroreflectivity versus sign age indicated that many retroreflectivity readings still 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 five years longer than the manufacturer warranty periods. For conservative purposes, agencies could consider a sign to be approaching the MUTCD minimum retroreflectivity level at approximately five years past the manufacturer warranty based on the results of this research.