Changes in fatal and nonfatal crash rates on a toll highway.

Rates of crashes, crashes with injuries, and crashes with fatalities were lower during the 6 months of March 1-August 31, 1974, following a 5-15 mph (8-24 kph) decrease in speed limits on the Illinois Tollway, than the corresponding rates for any of the 6 preceding years, 1968-1973. During the same months of 1968-1974, rates of crashes and of crashes with injuries showed peaks without consistent trends, but rates and percentages of fatal crashes decreased. The data agree with the hypothesis that reducing speed limits on toll roads may lead to substantial reductions in rate of crashes and injuries.