On the relationship of crash risk and driver hours of service

Time-dependent logistic regression and case-control sampling are applied to derive a sample of 231 crashes and 462 non-crashes during 2004 for three national-scale trucking companies. The analysis focuses on changes in crash risk associated with driving up to 11 hours in one duty period and multi-day driving schedules over 7 days. Separate analyses of sleeper and non-sleeper crash risk are conducted as the risk factors associated with these operations were found to be different. Considering all the data together, except for an increase in the second hour, crash risk is statistically similar for the first 6 hours of driving and then increases non-linearly after the 6th hour. The 11th hour has a crash risk more than 3 times the first hour. Multi-day driving schedules are also associated with statistically significant crash risk increases of comparable magnitude to driving time. Non-sleeper operation crash risk is strongly associated with multi-day driving, somewhat more so than with driving time. Sleeper operation crash risk has strong association with driving time, with particularly increased risk in hours 8 through 11.