Effect of driver hours of service on tractor-trailer crash involvement

September 1987

Crashes involving large trucks are a major problem on U.S. highways. Large truck crashes on interstate highways in Washington State were investigated using a case-control study design. For each large truck involved in a crash, three trucks were randomly selected from the traffic stream at the same time and place as the crash but one week later and inspected by Commercial Vehicle Enforcement officers of the Washington State Patrol. Driver factors (age of driver, hours of driving, and logbook violations) and truck operating characteristics (carrier type, carrier operation, truck load, and fleet size) that might affect crash involvement were analyzed for the study population of tractor-trailers. A logistic regression model was used to estimate the adjusted odds ratio for each factor. Driving in excess of eight hours, drivers who violate logbook regulations, young drivers, and interstate carrier operations were found to be associated with an increased risk of crash involvement. Trucks operate d with equipment defects were also significantly overinvolved in crashes. The relative risk of crash involvement for driver whose reported driving time exceeded eight hours was almost twice that for drivers who had driven fewer hours.