b1b4170c_cal_Agencies___FHWA_HRT_07_042__Reported_Impacts
[Agency/Location] Indiana DOT (9) [Comments] The data collection did follow ASTM procedures, but it is not believed that this had an impact on the conclusions. The agency only uses Type II material, so the results are less generally applicable. [Implications] Impacts of new requirements considered low. Good example of how data can be used to justify extending replacement cycle. Useful insights on wiping effects that can be included in the procedures. [Reported Impacts] 
Retroreflectivity was field measured for a sample of signs in five parts of the State. Data indicated that more than 90% of the signs met or exceeded the minimum levels proposed by FHWA in 1998. Data analysis found no effect for cleaning of signs before measurement and no effect associated with differences in environmental factors in different parts of the State. Recommendation to the State to increase the replacement cycle for all but stop signs to 12 years.
Maintaining Traffic Sign Retroreflectivity: Impacts on State and Local Agencies - FHWA-HRT-07-042