FATAL CRASH RATES FOR TRACTOR-TRAILERS BY TIME OF DAY

This study attempts to develop a measure of the fatal crash rate of large trucks over the 24-hour day. Crash data on tractor-trailers were taken from the Fatality Analysis Reporting System (FARS) database for 1997, as compiled by the National Highway Traffic Safety Administration (NHTSA). This data set contains details on fatal crashes, including the crash time. Truck activity by hour-of-day was taken from selected state continuous weight-in-motion (WIM) data at automatic traffic recording devices, also for 1997. These two data sets were combined to develop a per-mile rate of fatal crashes that involve large trucks for each hour of the day. Specifically, this study compares the fatal crash rate on freeways, Interstates, and expressways for overnight travel (Midnight to 6 AM) to that of the rest of the 24-hour day. This analysis found that for one segment of the large truck population - tractor-trailers - the fatal crash rate for this class of roadways is relatively stable and does not increase substantially during overnight travel (Midnight to 6 AM). By contrast, passenger car and light truck travel shows a much higher observed fatal crash rate per mile traveled for overnight travel (Midnight to 6 AM) than for the rest of the 24-hour day.