Hours of Sleep and Fatigue in Motor Carriage

I. INTRODUCTION Fatigue is prevalent among truck drivers. McCartt et al. (1997) in a study of U.S. long-haul drivers, found that two-thirds of drivers reported driving while drowsy within the previous month and roughly a quarter reported that they had fallen asleep at the wheel at least once in the last year. Using Australian data, Arnold et al. (1997) found that 14% of truck drivers had nodded off behind the wheel at least once in the nine months prior to the survey. Additionally, they found that 5% of the drivers had been involved in an accident and 12% of these drivers attributed their crashes to fatigue. Jones and Stein (1987), in a survey of crashes involving large trucks on interstate highways in Washington, found that drivers who drove longer than eight continuous hours were almost twice as likely to be involved in a crash than those who had driven less than eight hours. They also found that interstate carriers had a higher relative risk of crash involvement than intrastate carriers. The higher relative risk of these drivers was attributed to fatigue. The number of fatalities involving large trucks has been largely unchanged over the past 20 years. However, because the number of registered large trucks has increased by 37%, accompanied by a 91% increase in the number of miles driven by large trucks, the number of accidents per truck or per mile has actually decreased. Despite this improvement, truck safety remains an important public policy issue. In 2001, there were 2.4 fatal crashes per 100 million miles driven for large trucks, compared with 1.5 fatal crashes for 100 million miles driven for passenger vehicles (Federal Motor Carrier Safety Administration [FMCSA] 2003). The University of Michigan Transportation Research Institute (UMTRI) study of fatalities due to heavy truck collisions finds that in 2000 there were 5275 fatalities resulting from heavy truck accidents. Slightly over one-third (36.6%) of these accidents were attributed to truck driver-related factors. Nearly 6% of these were attributed to drowsiness or sleeping at the wheel (109 accidents), and nearly 15% (284 accidents) were attributed to inattentiveness. (1) These two factors combined are significantly larger than those accidents attributed to alcohol or drug consumption on the part of truck drivers (31 and 115, respectively) (UMTRI 2000). If one considers drowsiness and chemical impairment as "preventable" accidents in the sense that the driver's behavior could be modified to significantly reduce the probability of this type of accident, then understanding the factors contributing to fatigue is important from a policy perspective. The average annual costs of truck crashes between 1997 and 1999 were $19.6 billion. This can be decomposed into costs due to productivity loss ($6.6 billion), medical costs ($11.33 billion), and quality of life costs ($9.6 billion). The average cost of a crash involving a large truck is $59,153 (Zaloshnja et al. 2004), and this cost is larger for accidents involving fatality. Not surprisingly, the quality of life costs from a serious injury or fatality caused by a truck accident are more likely to be borne by the driver of the other vehicle(s) involved in the crash. This holds true for most accidents involving a weight disparity between vehicles (Eicher et al. 1982; Evans 1991; White, 2003). The UMTRI data on fatal accidents involving medium and large trucks support this. Nearly 15% of the fatalities were drivers or passengers of the truck, approximately 8% of fatalities were nonmotorists, and 77% were drivers or passengers of nontruck vehicles. The costs of these accidents, then, are not primarily being borne by the truck drivers and their firms but by then ontrucking public. This article addresses two issues. First, how much sleep do drivers get, and how does this vary with operating characteristics? Second, what factors, including sleep, influence falling asleep at the wheel? …