A survey of heavy vehicle drivers and other motorists was conducted during 1976. Survey methodology and results were presented in a previous report which described several ways in which the sample of truck drivers differed from the sample of other motorists. The present report describes and discusses further analyses of the data to determine whether the difference shown to exist between the two samples contributed to the larger number of traffic crashes reported by truck drivers than by other motorists. The outstanding difference between the two samples was the larger amount of time spent at the wheel by truck drivers and this was found to be the most important predictor of traffic crash frequency. When this exposure factor was controlled, other variables were shown to be unrelated to traffic crash frequency. The critical point at which truck drivers 'crash rates rose was 55 hours driving time in a typical week. Those who drove for less than 55 hours per week were likely to have a lower crash rate per million hours driving time than those who reported driving for 55 hours or longer in a typical week.
Samenvatting