The Sleep of Long-Haul Truck Drivers

To the Editor

The article by Mitler et al. on the sleep of long-haul truck drivers (Sept. 11 issue)¹ presents data on drowsiness. The authors state, “Of the total of 29,310 six-minute video recordings of the drivers' faces that we analyzed, 1989 of the segments (7 percent) were judged to show a drowsy driver.” However, according to a footnote to Table 4, it appears that the numerator for this percentage is derived from the sampled segments (consisting of one 6-minute segment per 30 minutes of observation time) and the denominator is the universe of segments from which the sample was drawn. With the use of standard methods of statistical inference from samples,² the correct calculation should have been the number of sampled segments in which a driver was seen as drowsy divided by the number of sampled segments reviewed. With this calculation, 34 percent of sampled segments included drivers who were judged to be drowsy during at least part of the segments, with corresponding increases in other categories of driving schedule and time of day. Therefore, segments involving drowsiness occurred more than four times as often as reported.

The study has additional weaknesses that limit the conclusions that can be drawn. Volunteer drivers were neither randomly assigned to the four driving-schedule groups nor rotated through each group. Thus, the drivers were not necessarily comparable. For example, the mean ages of the two Canadian driver groups were significantly lower than those of the U.S. “steady-day” group, on the basis of 95 percent confidence intervals for the means,² notwithstanding the authors' statement that “drivers were selected so that the average age of the drivers on each schedule was similar.” Another shortcoming is that the observers who rated the video recordings of the drivers' faces for drowsiness were aware of the time of day and ambient light level for each segment. If the observers expected that the drivers would be drowsier at night, they may have been more likely to consider the drivers drowsy on video recordings made at night. Although the investigators report measures taken to ensure consistent scoring of polysomnographic data, including the rescoring of randomly selected records, they report no similar reevaluations of randomly selected video segments.

Elisa R. Braver, Ph.D.
Janella F. Pantula, Ph.D.
Insurance Institute for Highway Safety, Arlington, VA 22201

To the Editor

The ambitious report on the sleep patterns of long-haul truck drivers acknowledges only the funds received from the Federal Highway Administration (“Supported by contracts [DTFH61-89-C-096 to Essex Corporation and DTFH61-90-C-053 to the Trucking Research Institute]”) and subcontracts to the Scripps Clinic.

The acknowledgment does not mention that funds were also contributed by the American Trucking Associations' Trucking Research Institute. In 1992, the American Trucking Associations Foundation announced its intention “to raise $476,000 to fund its share of the project.”¹ The Federal Highway Administration's briefing package for the study stated that the Trucking Research Institute “is funding part of the data collection and analysis.”² Support from the Trucking Research Institute is noted in the Federal Highway Administration's report describing the same study.³

The Trucking Research Institute is a research affiliate of the American Trucking Associations Foundation, a nonprofit arm of the American Trucking Associations, which is a trade association for the trucking industry. Failure to acknowledge the support of the Trucking Research Institute is especially troubling because the Federal Highway Administration is in the process of revising its rules that limit driving hours for interstate truck drivers and has described this study as providing “a technically sound basis for evaluating the current hours-of-service requirements for commercial motor vehicle operators.”⁴

The trucking industry has a financial interest in any changes in work-hour limits (some American Trucking Associations affiliates have called for lengthening the permissible driving period from 10 hours to 14 hours) and clearly has a financial interest in this study. Table 4 of the article shows that drivers on 13-hour schedules had more than twice as many video-recorded episodes of drowsiness (identified on the basis of drooping eyelids and a bobbing head) as drivers on 10-hour schedules.

Susan P. Baker, M.P.H.
Johns Hopkins School of Public Health, Baltimore, MD 21205-1996

To the Editor

The analysis by Mitler et al. failed to emphasize the impact of fatigue on fatal truck crashes. Their study suggests that most of the drivers were sleeping less than five hours per night. In 1996, in the United States, more than 44,000 persons died and 2.3 million were injured from car crashes. Despite the fact that trucks account for less than 4 percent of the vehicle fleet, nearly 18 percent of the deaths resulted from truck crashes.

Several lines of evidence point to inadequate sleep as a major culprit in truck crashes. A survey of tractor-trailers in four states indicated that 10 to 23 percent of drivers had fallen asleep while driving in the previous month.¹ The National Highway Traffic Safety Administration (NHTSA) cited drowsiness and fatigue as factors in 15 percent of single fatal truck crashes and estimated that in 1990, 31 percent of 182 large-vehicle crashes that were fatal to the drivers were attributable to the drivers' fatigue.²

Large mass, very high mileage, and long operational life mean that tractor-trailer trucks, in particular, have the highest involvement in fatal crashes, despite an overall low risk of total crashes per miles traveled. When speed limits were raised from 90 to 100 km per hour (56 to 63 mph) in Israel, deaths from truck crashes increased by 60 percent, contributing to 40 percent of the additional road toll.³ A recent NHTSA study found that 67 percent of drivers with irregular schedules had been involved in fatigue-related crashes, as compared with 38 percent of drivers with regular schedules. The most important predictive factor in a fatal crash was the duration of the driver's most recent sleep period and the total hours slept.⁴

It is time to enforce reduced speed limits for trucks and mandatory rest periods for truck drivers, particularly at night. Eliminating incentive premiums and providing higher salaries and reasonable work conditions are essential steps in reducing fatigue-related fatal truck crashes.

Paul Barach, M.D., M.P.H.
Massachusetts General Hospital, Boston, MA 02114

Gerry Ben David, Ph.D.
Jerusalem College of Technology

Elihu Richter, M.D., M.P.H.
Hebrew University, Jerusalem 91120, Israel

To the Editor

While driving, 56 percent of the truck drivers showed evidence of drowsiness on video recordings, and 2 of the 80 drivers had one episode each of stage 1 sleep, as detected by electroencephalography. I cannot help but wonder how high these numbers would have been had the study been conducted with interns, residents, and fellows instead of truck drivers.

David A. Benaron, M.D.
Stanford University School of Medicine, Stanford, CA 94304

To the Editor

Could there be a connection between the “near absence” of teaching about sleep in America's medical schools, noted by Dement in his editorial,¹ and the observation that physicians and medical trainees continue to work extended shifts, sometimes lasting 36 or more consecutive hours? Despite recent regulations, many physicians consistently work while fatigued. If sleep deprivation is deemed dangerous for truckers, there should be similar concern about those who are entrusted with the care of patients who are seriously ill.²

Michael J. Green, M.D.
Pennsylvania State University College of Medicine, Hershey, PA 17033-0850