Analysis of In-Service Traffic Sign Retroreflectivity and Deterioration Rates in Texas

Roadway traffic signs are a fundamental medium for conveying critical information to the road user. In 2009, the Manual on Uniform Traffic Control Devices (MUTCD) set minimum retroreflectivity requirements for such signs. Developing sign management strategies on the basis of service life is one approach to achieving compliance with minimum MUTCD sign retroreflectivity requirements. Generating deterioration rates and prediction models from a sample of in-service sign measurements is one method for establishing expected service life. In 2009, researchers collected a sample of 859 ASTM D4956 Type III retroreflectivity signs in seven regions of Texas. The objective of this study was to assess the compliance of Type III signs throughout Texas and to generate useful data that would improve sign maintenance practices. The overall sign sample compliance rate was 99%. The observed likelihood of failure was 2% for signs that were between 10 and 12 years old and 8% for signs that were 12 to 15 years old. The linear prediction models revealed differences in deterioration rates between the regions. The differences ranged from −2 to −8 candelas (cd)/lx/m² per year for white sheeting and −1 to −12 cd/lx/m² per year for yellow sheeting. Models exhibited poor correlations between predicted and measured data, and the R-squared values ranged from .10 to .30. Despite the weak relationships, the models revealed insightful trends and provided a broad perspective on the Texas Department of Transportation's current sign practices. Deterioration rates and prediction models can be valuable components in a comprehensive sign maintenance program, but by themselves they do not ensure compliance with sign retroreflectivity requirements.