THE SAFETY IMPACT OF THE 65 MPH SPEED LIMIT: A CASE STUDY USING ALABAMA ACCIDENT RECORDS. FINAL GRANT REPORT

This study investigated the effects of the change of the speed limit on rural Interstate roadways from 55 to 65 mph in Alabama, which took effect on August 1, 1987. The primary source of data was the accident records, which were compared for several test and control areas as well as one year time periods before and after. Traffic volume and speed data were also analyzed to properly interpret the results of the accident data analyses. Both average speed and traffic volume increased more on the rural Interstates than on other roadway types. Significant incrases in PDO and injury type accident frequencies were correlalted with the speed limit change. Spillover effects were found on 55 mph Interstates but not on other roadway types. Several other factors were analyzed, inlcuding weather, vehicle type, roadway character, number of vehicles, collision events, and the use of seat belts.