Validation of U.S. Road assessment program star rating protocol: Application to safety management of U.S. roads

The U.S. Road Assessment Program, in cooperation with road assessment programs in other countries, has developed a protocol to assign ratings to roads on the basis of the presence or absence of key design features related to safety. This protocol rates roads by assigning them one to five stars according to approximately 20 key roadway safety features. A recently developed web-based software tool uses the roadway inventory data on which the star ratings are based to identify cost-effective safety improvement programs for the road networks covered by the ratings. The research results are presented to validate the relationship between the star ratings and crash rates for selected roadways. The research developed star ratings for approximately 3,000 mi of rural and urban roadways of various types in Iowa and Washington State and compared the star ratings with crash rates for the same roads. Relationships between star ratings and crash rates were found for two-lane undivided highways, four-lane undivided highways, and four-lane divided nonfreeways. No clear relationships could be demonstrated for freeways because the design characteristics of freeways are very uniform.