Literature Review on Health and Fatigue Issues Associated with Commercial Motor Vehicle Driver Hours of Work (2005) / Chapter Skim
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Part II Review of References Related to Public Comments
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rules for commercial truck drivers with a planned implementation date in January 2004. After substantial amounts of training and preparation by government and the trucking industry, those new HOS rules went into effect January 4, 2004.
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, or comprehensive analysis of economic benefits and costs of the proposed rule, as was filed in the docket for the April 2003 final rule. Within the responses to this request for comments on this announcement were some 266 references to studies, articles, and literature relating to the health and fatigue effects of the HOS regulations.
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and for nuclear power plant and manufacturing operations • Project manager for several Transport Canada projects involving literature review and development of experimental protocols related to fatigue and minimum recovery periods for CMV drivers • Forensic consultant with expertise on car and truck driver fatigue and shiftscheduling issues • Consultant to both Canadian and U.S. governing bodies on trucking industry hours of service regulations
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Dianne Davis, M.Eng. • Associate Consultant, Human Factors North, Inc.
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Several investigations of the acute biochemical effects of acute sleep restriction supported this concern due to the increase in risk factors for diabetes and obesity and an additional study noted that self-reported daily short sleep duration was associated with an increase in the rate of diabetes. PROCESS AND METHODOLOGY Literature Search Source and Terms FMCSA provided a list of 266 references cited in public comments on the advanced NPRM.
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As BMI or obesity may itself be associated with short sleep duration based on the studies of acute sleep deprivation, this may not be an appropriate control as the effect may be mediating rather than confounding.
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Although chronic sleep loss is common in today's society, many people are unaware of the potential adverse health effects of habitual sleep restriction. Under strict experimental conditions, short-term restriction of sleep results in a variety of adverse physiologic effects, including hypertension, activation of the sympathetic nervous system, impairment of glucose control, and increased inflammation.
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Short-term sleep restriction results in impaired glucose tolerance. To test whether habitually short sleep duration increases the risk of developing diabetes, we studied a cohort of 70,026 women enrolled in the Nurses Health Study, without diabetes at baseline, and who responded to a question about daily sleep duration in 1986.
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In 1985, the number of male union workers at the 4 companies whose job history could be characterized was 55,750, and in 1999, it was 72,666. A retrospective cohort study of workers from the cooperating trucking companies and the Teamsters union alive in 1985 with mortality assessed through 2000 would have a greater than an 80% power to detect a relative risk of lung cancer of 1.25 to 1.29 attributable to diesel exposure.
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128 Industry Sector: Major Limitations: Findings Directly Related to HOS (include page references) : Reviewer's Notes:
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This case-referent study investigated the lung cancer risk from occupational exposure to diesel exhaust; mixed motor exhaust; other combustion products, asbestos, metals, oil mist, and welding fumes. All cases of lung cancer in males aged 40 to 75 years old among stable residents of Stockholm County, Sweden, were identified from 1985 to 1990.
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6 of 14) "Increased risks of lung cancer were noted in the highest quartiles of cumulative exposure to diesel exhaust, combustion products and asbestos.
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reviewed for the HOS literature search in Part I Reviewer: Complete Title: Abstract: Methodology: Scope of Work: Sample Size: Industry Sector: Major Limitations: Findings Directly Related to HOS (include page references)
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This study offers an opposing view to the studies showing adverse health effects of sleep deprivation. 132 Reviewer: Complete Title: Abstract: Methodology: Scope of Work: Sample Size: Industry Sector: Major Limitations: Findings Directly Related to HOS (include page references)
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Reviewer: Complete Title: Abstract: Methodology: Scope of Work: Sample Size: Industry Sector: Major Limitations: Findings Directly Related to HOS (include page references) : Reviewer's Notes:
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Changes in cortisol levels with sleep deprivation are similar to that seen in normal aging. 134 Reviewer: Complete Title: Abstract: Methodology: Scope of Work: Sample Size: Industry Sector: Major Limitations: Findings Directly Related to HOS (include page references)
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In Western societies, where chronic sleep restriction is common and food is widely available, changes in appetite regulatory hormones with sleep curtailment may contribute to obesity. All employees aged 30 to 60 yr of four state agencies in south central Wisconsin were mailed a survey on sleep habits, health, and demographics in 1989.
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No association was found with sleep duration and glucose or insulin levels. 136 Findings Directly Related to HOS (include page references)
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Reviewer: Complete Title: Abstract: Methodology: Scope of Work: Sample Size: Industry Sector: Major Limitations: Findings Directly Related to HOS (include page references) : Reviewer's Notes:
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counties face a cancer risk from diesel exhaust greater than 100 deaths per million population. People living in eleven urban 138 Reviewer: Complete Title: Abstract: Methodology: Scope of Work: Sample Size: Industry Sector: Major Limitations: Findings Directly Related to HOS (include page references)
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This literature review is consistent with the conclusion that increased weekly working hours and the probable concomitant increased exposure to diesel exhaust is likely to contribute to an increased risk of cancer. It is also consistent with the conclusion that this impact is likely mitigated by changes in cab and engine design currently incorporated in new vehicles.
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The researchers found that while the night shifts made drivers feel more tired than day shifts, they did not produce significantly poorer performance on tests of PVT and Mackworth Clock, "suggesting that night drivers can manage their fatigue." Over a typical workweek of five consecutive 10- to 12-hour shifts, there was a significant increase in subjective ratings of fatigue by all drivers. Night shift drivers worked longer shifts than day shift drivers and spent much more of their working time driving than day shift drivers "which might predict that night shifts would be more tiring than day shifts." However, the authors suggest that night shift drivers may have performed as well as day shift drivers as they may be "especially tolerant of fatigue or skilled at managing fatigue" and because they organize their sleep differently (e.g., napping in the hours before their first shift of the week)
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Twenty-six percent of the drivers, assuming average legal speed limits of 55 mph, were found to have violation-inducing schedules. Drivers most likely to have these schedules included solo drivers, drivers hauling refrigerated loads, regular route drivers, and those with longer current trip distances.
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reports that more than 25% of the accidents occurred in the first hour, and twothirds in the first 4 hours, and that "only about 4 percent of all medium and heavy truck drivers involved in a fatal crash reported driving more than 8 hours at the time of the accident." The authors note that this pattern is driven "by exposure, not risk" as the "nature of the exposure distribution will always keep the number of accidents after many hours driving a small proportion of the total, even with dramatic increases in risk with hours driving." When differences in exposure were considered the authors found the following: 1. "The relative risk of fatigue given involvement in a fatal accident follows the circadian rhythm." 2.
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There was a highly significant main effect of shift, in that risk increased by 18.3% on afternoon shifts and by 30.4% on night shifts relative to the morning shift. There was also a consistent trend in accident risk over four successive nights.
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Inexperienced drivers had higher reaction times than experienced drivers in both sleep-deprived and non-sleep deprived conditions." The results of these studies suggest that there are cumulative performance consequences to limiting sleep to even as much as 6 hours per day, and that the effects of sleep deprivation may be more for inexperienced drivers. Sleep Restriction, Time of Day, and Crash Risk NTSB (1995)
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Drivers were interviewed and approximately 20% reported penalties from their motor carriers for late deliveries. At the conference, Truck Safety: Perceptions and Reality, the attendees concluded that current HOS regulations in Canada and the United States are too narrowly focused to reduce the incidence of driver fatigue in truck accidents.
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, examining simulated driving performance during one night of prolonged of wakefulness. They found that "mean tracking, tracking variability, and speed variability 18.5 and 21 h of wakefulness produced changes of the same magnitude as 0.05 and 0.08% blood alcohol concentrations, respectively." In addition, they found that alcohol consumption produced changes in speed deviation and off-road occurrences of greater magnitude than the corresponding levels of prolonged wakefulness.
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. driving performance was in a number of respects, affected similarly by prolonged wakefulness and by alcohol.
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which consisted of the "average speed a vehicle would need to maintain to reach the next destination without being late and with the driver obeying the driving times mandated by HSR." Previous driving time was "estimated by determining the time required to complete the driver-reported mileage driven over the previous seven days." In the analysis, three scenarios were examined assuming average road speed limits: 55 mph, 60 mph, and 65 mph. Weekly driving time was estimated by assuming an average speed, and then determining the driving time necessary to cover the driver's weekly mileage.
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37, "Using the 55 mph average speed limits, an estimated 26% of all drivers had violationinducing schedules. Ignoring the 60- and 70-hour rules, 15% of the drivers would have had such schedules due to the demands of the current trip.
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Again assuming 55 mph average speed limits, 28% of the solo drivers, but only 11% of the team drivers, would have to violate HSR and/or speed limits to stay on schedule. Due to these differences, the analysis focused on solo drivers.
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, sleep latency, and subjective sleepiness. According to the authors, of the measures taken in the larger study, the PVT was chosen for this paper because it was the most sensitive to the effects of sleep restriction and was the least subject to learning effects." The purpose of the study was to empirically determine the effects of 3, 5, 7 and 9 hours of sleep over 7 consecutive days on objective and subjective alertness and objective performance.
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If less than 4 hr of sleep per night is obtained, daily decrements in performance capacity may be unavoidable – at least across a 7-day period of sleep restriction." p. 10, "The present findings suggest that core sleep might best be considered as the minimum amount of sleep needed by the brain to achieve a state of equilibrium in which alertness and performance are maintained at a stable but lower-than-normal level.
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The drivers interviewed for this study were interviewed during summer morning hours at two specific sites. As a result, the authors note that "whether afternoon or nighttime truck traffic differs from morning traffic in terms of shippers' requested delivery schedules, whether these sites differ from others in the United States, and whether there are seasonal variations in motor carrier characteristics at these sites cannot be assessed from existing data." 1.
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7. Few dispatchers reported penalties imposed by shippers for late deliveries although 20% of drivers reported penalties from their motor carriers for late deliveries.
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Truck driver fatigue is the dependent variable and power unit type, trip distance, for-hire versus private carriers, time of day, and hours driving are the independent variables for the analysis. Over 27,463 medium and heavy trucks involved in fatal accidents over the 6-year period Medium and heavy trucks The coding of fatigue is taken from the "driver-related factors" variables in FARS which relies on the original police accident report.
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More than 25% of the accidents occurred in the first hour, and two-thirds in the first 4 hours. "Only about 4 percent of all medium and heavy truck drivers involved in a fatal accident reported driving more than 8 hours at the time of the accident." The authors note that this pattern is driven "by exposure, not risk" as the "nature of the exposure distribution will always keep the number of accidents after many hours driving a small proportion of the total, even with dramatic increases in risk with hour driving." (In other words, there are more 4-hour trips than 8-hour or 12-hour trips)
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fatigue. It is likely that there is a strong interaction between time of day and hours of driving.
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This article reviews the literature on shiftwork safety and the "related evidence on sleep duration, fatigue, and performance capabilities." It focuses on studies in which "real measures of injuries and/or accidents can be related both to the time of day and/or to the point within the shift system that they occurred." The studies look at specific features of shifts such as type of shift, length of shift, and number of successive shifts. The authors found a highly significant main effect of shift (i.e., risk increased on afternoon and night shifts relative to the morning shift)
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While there was no evidence of a main effect of successive shifts using the repeated measures analysis of variance, the chi-square test yielded a significant effect of successive shifts, however it was substantially smaller than that over successive night shifts. On average, risk was about 2% higher on the second morning/day, 7% higher on the third morning/day, and 17% higher on the fourth morning/day shift than on the first shift.
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The following figures show the estimated relative risks for different spans and lengths of day shifts (Figure 1) and night shifts (Figure 2)
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5, "Based on these pooled frequencies, risk increased in an approximately linear fashion, with an increased risk of 18.3% on the afternoon shift, and of 30.4% on the night shift, relative to the morning shift…This finding suggests that when the a priori risk appears to be homogeneous across the three shifts, there is a consistent tendency for the relative risk of incidents to be higher on the afternoon shift than on the morning shift, and for it to be highest on the night shift." p. 6, "There is also a consistent trend in accident risk over successive night shifts .
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This article describes a study on the risk of crash with respect to driving hours and other time intervals related to the driver's working lives. A ‘case' group of heavy vehicles involved in crashes were compared to a ‘control' group of vehicles.
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28 , "Crash involvement increases significantly after about 8 hours worked from the last 10 hour rest period." Driver Health No significant findings or assumptions concerning impact on health. Findings Directly Related to HOS (include page references)
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Truck accident data were analyzed to see if fatigue and circadian rhythm effects were present in truck accidents that seemed to be the result of failures in vigilance performance. Data was analyzed for three groups of drivers: dozing drivers, those who had had single-vehicle accidents, and those who had crashed into the rear end of other vehicles.
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… The evidence suggests that trips should not be scheduled so that drivers will still be on the road, after many hours of driving, at times of the day when their capabilities to attend to the driving task are at a low ebb." Driver Health No significant findings or assumptions concerning impact on health. Findings Directly Related to HOS (include page references)
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3, "It appears that WA drivers are no more likely to exceed weekly driving hours regulations than their Eastern States' counterparts, despite enforcement of driving hours regulations in the Eastern States." Reviewers: Title: Abstract: Methodology: Scope of Work: Sample Size: Industry Sector: Major Limitations: Findings: Findings Directly Related to HOS (include page references)
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3, "The Eastern States drivers were more likely to report that long driving hours and poor sleep were fatiguing than WA drivers, despite regulation of driving hours in the Eastern States." Driver Health No significant findings or assumptions concerning impact on health.
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130 long-haul tractor-trailer drivers, driving alone Long-haul tractor-trailer The authors note that a "precise estimate of hours of service violations cannot be calculated without knowing the actual speed distribution of the drivers in the sample." 1. 90% of the drivers were in violation of the HOS rules by more than 1 hour by the time they arrived at the Minnesota observation site with an assumed average trip speed of 40 mph.
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34, "At an assumed trip speed of 40 mph, 36% of the drivers missed more than 70% of required rest, 61% missed more than 50% of the rest, and 88% missed more than 10% of the rest." p. 34, "At an assumed trip speed of 50 mph, 9% of the drivers missed more than 70% of the required rest, 20% missed more than 50% of the rest, and 48% missed more than 10% of the rest." p.
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Driver Fatigue p. 15, "What is important from this study is that the relative risk of crash involvement for drivers driving more than eight hours is almost twice that for drivers with fewer hours behind the wheel… the risk from driving long hours increases for drivers operating between 12:01 a.m.
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Their study indicates an increased accident risk for night drivers after 3 to 4 days of driving but less concern for daytime drivers with respect to a crash immediately following a 3- to 4-day period of driving. The data were obtained from a "pony express" type operation, which operates coast to coast with no sleeper berths.
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79 accident and near-accident investigations were analyzed Train drivers The authors note that their results must be interpreted with caution as the investigations they analyzed frequently contained relatively sparse information on the working conditions at the time of the incident. As a result, they were required to infer if fatigue or stress was present at the time of the accident (see Methodology)
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Findings Directly Related to HOS (include page references)
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"There were no effects of driving experience for any of the driving performance measures." 3. Sleep deprivation for up to 36 hours significantly reduced the ability of all drivers to maintain a steady position in the lane and a stable speed.
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These findings are relevant to those who are placed in situations where driving after a period of SD is unavoidable, as in the transportation industry." Driver Health No significant findings or assumptions concerning impact on health. Findings Directly Related to HOS (include page references)
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1,924 cases (i.e., 694 accidents and 1,230 non-accidents) were used for modeling Less-than-truckload; no sleeper berths While "time-dependent covariates play a key role in accident analysis," the authors note that the "shortage of time-varying data makes it difficult for a researcher to consider further accident analysis and solutions." For example, high traffic volume could be one of the reasons for the highest accident risk occurring between 4:00 and 6:00 p.m.
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The 8th and 9th hr show a further increase, approximately 80 and 130 percent higher than the first 4 hr." p. 7, "Time of day had an effect on subsequent accident risk, but the effect was not as strong as for driving experience or driving hours.
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the current regulations have an impact on accident litigation. In addition to discussing the various factors that determine level of sleepiness and fatigue-related accident risk, they briefly discuss alternative paradigms to HOS regulations that minimize the risks associated with excessive employee work hours and fatigue.
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." An analysis of the 96-hour duty-sleep history prior to 107 single-vehicle heavy truck accidents. 107 single-vehicle heavy truck accidents Heavy truck drivers The definition of fatigue may be unduly restrictive, given that it involves driving at least 16 hours, and drivers may be fatigued before this point.
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2, "The statistically significant analysis determined that the most important measures in predicting a fatigue-related accident in this sample are the duration of the last sleep period, the total hours of sleep obtained during the 24 hours prior to the accident, and split sleep patterns." Driver Health No significant findings or assumptions concerning impact on health. 180 Findings Directly Related to HOS (include page references)
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As one case was eliminated from the analysis, the study analyses 181 heavy truck accidents involving 185 case vehicles and drivers. Fatigue was considered a probable cause of the accident if the driver was estimated to have been on duty for more than 15 consecutive hours (the current legal limit)
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"The most frequently cited accident probable cause or factor in fatal-to-the-driver heavy truck accidents was fatigue (57 cases or 31 percent) , followed by alcohol and other drug impairment (53 cases or 29 percent)
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These detailed comparisons further highlight the elevated risk posed by night driving compared to the baseline regular daytime driving." Reviewers: Title: Abstract: Methodology: Scope of Work: Sample Size: Industry Sector: Major Limitations: Findings: Findings Directly Related to HOS (include page references)
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Driving schedules C7 to C9 (averaging about 100 drivers in each group) involve drivers with night and early morning driving and include large amounts of off-duty time one or two days prior to the day of interest; all show elevated crash risk.
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984, "In terms of sedative effects as measured by the MSLT, sleep loss was 2.7 times more potent, meaning that 8 hours of sleep loss is equivalent to 2.16 g/kg of ethanol and 2 hours of sleep loss is equivalent to 0.54 g/kg." Reviewers: Title: Abstract: Methodology: Scope of Work: Sample Size: Industry Sector: Major Limitations: Findings: Findings Directly Related to HOS (include page references)
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984, DAT measures -- tracking deviations and central reaction times: "Central reaction time was slowed by sleep loss (F = 6.20, P < .002) , with 8 hours and 6 hours of TIB differing from 0 hours of TIB.
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Database analysis to compare accident rates between locations and times for different types of fatigue. 1988–1989 truck accident data Trucks n/a 1.
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." p. 171, "The effect of circadian fatigue on truck accident rates appears to be additive to the effect of industrial fatigue.
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Cognitive throughput performance after 14 days of sleep restriction was equivalent to that observed after 1 night without any sleep. Subjects in the 6 h sleep period condition also reached levels of impairment equivalent to those observed after 1 night of total sleep loss for lapses in behavioral alertness and working memory performance." 4.
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. the two modes of sleep loss yielded similar maximum deficits for PVT performance but chronic sleep restriction resulted in much greater cumulative sleep loss than did 3 days of total sleep deprivation.
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Actigraph data was also collected to provide objective measures of the timing and quality of their sleep. The researchers found that while the night shifts made drivers feel more tired than day shifts, it did not "produce significantly poorer performance, suggesting that night drivers can manage their fatigue." Fifty-four Australian drivers participated in the study: 22 permanent day shift drivers, 21 permanent night shift drivers, and 11 rotating shift drivers.
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The authors note that all of the drivers in this study "were being affected by restricted sleep and that any differential effects of night work may be overshadowed by this effect." In addition, they note that night shift drivers performed as well as day shift drivers as they are experienced professional drivers "who are well-suited to cope with the demands of the road transport industry by organizing their work-rest." 5. Night shift drivers worked longer shifts than day shift drivers and spent much more of their working time driving than day shift drivers "which might predict that night shifts would be more tiring than day shifts." However, the authors suggest that night shift drivers may have performed as well as day shift drivers as they may be "especially tolerant of fatigue or skilled at managing fatigue" and because they organize their sleep differently (e.g., napping in the hours before their first shift of the week)
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27 long-distance truck drivers (mean age: 38.4; driving experience: 15.9 years) Professional long-distance drivers The authors note that the analysis of the results of this study was hampered to some extent by missing data, particularly in the data collected during the trip.
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In contrast, when on flexible trips heart rates were much slower at the beginning of the trip, but increasing such that by the end of the trip they had much faster heart rate than the other trip types. This suggests that when on flexible trips, drivers had lower alertness, based on the heart rate measure, at the beginning of the trip but their alertness increased by the end of the trip." Driver Fatigue/Alertness p.
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Drivers on flexible trips showed few differences on any of the cognitive or on-board performance tests compared to control trips. It seems that the requirement to comply with the regulated work-rest arrangement does not enhance the drivers' cognitive functioning or work performance, nor does it reduce the amount of fatigue that drivers report.
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