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93 alert if the driver had poorer self-perceived health were reported by these drivers (p < 0.05). Many drivers and (Hakkanen and Summala 2000). company representatives reported fatigue to be a problem for Poorer lane tracking and gear shifting related to poorer other drivers, but considered themselves or their companies' general fitness. drivers to be relatively unaffected by fatigue. There were dif- Height/weight (a surrogate measure for general fit- ferences between drivers' and companies' perceptions about ness) was correlated with lane performance and shifting causes of fatigue, and strategies that should be used to man- performance. These correlations were absent for more age it. The results obtained from these drivers in an unregu- cognitive, less physical tasks (O'Neill et al. 1999). lated state were compared with earlier findings from drivers in states where driving hours restrictions are in place. RESEARCH LIMITATIONS Balkin, T., Thome, D., Sing, H., Thomas, M., Redmond, D., Wesensten, N., Williams, J., Hall, S., and Belenky, G. The most notable lack of research concerns recovery (2000). "Effects of sleep schedules on commercial motor requirements, particularly for night drivers. Long-distance vehicle driver performance." Department of Transporta- truck drivers frequently drive at night to avoid traffic and, tion, Federal Motor Carrier Safety Administration. because they work at night, must sleep during the day. Because The Balkin et al. (2000) study involved an actigraphic of circadian rhythms, we do not perform well at night, par- assessment of the sleep of 50 long- and short-haul CMV driv- ticularly during the early morning hours, and sleep obtained ers ages 21 to 65 for 20 consecutive days. The drivers wore during the day is shorter and of poorer quality than sleep the Walter Reed wrist actigraphs at all times except when obtained at night. Currently, HOS regulations treat daytime bathing or showering. In addition, they completed sleep logs and nighttime driving equally both in terms of hours permit- on driver's daily log sheets to gather subjective information ted and required recovery time. The new regulations will about sleep times; sleep latency; arousals during sleep; alert- allow for longer hours in a 7-day period provided the driver ness upon awakening; naps (number and duration); and self- takes a 34-hr reset period. Research concerning the accept- reported caffeine, alcohol, and drug use. The data from each ability of this reset period is very limited (a laboratory study actigraph were downloaded to a personal computer, and each of daytime performance finding good recovery after 1 night 24-hr actigraph recording period was examined for sleep in of sleep if previous night's sleep had been 7 or 9 hr, a study its entirety regardless of the duty status type or length indi- of team drivers in a remote area of Australia finding dramatic cated on the daily log sheet. recovery after a single overnight stop in the middle of a 4- to 5-day trip, a small on-road study showing that neither day nor Baas, P.H. (Transport Engineering Research New Zealand night drivers, and especially not night drivers recovered fully (TERNZ)), Charlton, S., and Bastin, G. (2000) "Survey of following a 36-hr reset). New Zealand truck driver fatigue and fitness for duty." 4th International Conference on Fatigue and Transpor- COMPLETE PRIMARY SOURCES tation, Fremantle, Western Australia. AND ABSTRACTS This paper presents recent research on compliance with current driving hours regulations, the effectiveness of using Arnold, P.K., Hartley, L.R., Hochstadt, D., and Penna, F. driving hours to predict fatigue, and alternative compliance "Hours of work, and perceptions of fatigue among truck and enforcement options. The paper describes results of a drivers." (1997). Accident Analysis & Prevention, 29 (4) major survey of truck driver fatigue in New Zealand, a review 47177. of international compliance and enforcement procedures, and Drivers and companies operating in the heavy road trans- research focusing on the social forces and influences that port industry were surveyed about drivers' hours of work and affect truck drivers. The survey of truck drivers was based on perception of the causes and magnitude of fatigue as an indus- interviews and performance tests collected from 600 truck driv- try problem. These drivers were operating in a state which, at ers at depots, wharves, markets, and other locations through- the time of the survey, did not restrict driving hours for heavy out the North Island of New Zealand. The initial results from haulage drivers. On the day of the interview, estimates based the first 100 drivers found a sizable number of drivers exceed- on retrospective and prospective reports, suggest that in a ing the allowable driving hours, high levels of fatigue and 24-hr period about 38% of drivers exceed 14 hr of driving, and sleepiness, and interesting differences between line-haul and 51% exceed 14 hr of driving plus other non-driving work. local delivery drivers. A related research project into the About 12% of drivers reported less than 4 hr of sleep on 1 or social processes/relationships that affect truck drivers has more working days in the week preceding the interview. resulted in a good understanding of the social conditions that These drivers are likely to be operating their vehicles while influence cultural change and the actions of truck drivers and having a significant sleep debt. About 20% of drivers reported fleet managers. In this paper we will have particular regard to less than 6 hr sleep before starting their current journey, but these processes in the construction of ideas concerning nearly 40% of dangerous events that occurred on the journey safety. This includes an understanding of the role of major

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94 stakeholders, such as freight forwarders and the enforcement including the driver's face; driving performance information, agencies with respect to drivers and their conditions, actions including steering, lane departure, and braking; sleeper-berth and understanding of the road transport industry. This knowl- environmental data, including noise, vibration, and tempera- edge coupled with the survey results and an understanding ture; subjective alertness ratings; and data from the Nightcap of compliance and enforcement alternatives will be used to sleep monitoring system. The results obtained are provided in explore potential fatigue management options. (a) For the cov- the document. ering entry of this conference, see ITRD abstract no. E204477. AN: E204480 Feyer, A.M., Williamson, A., and Friswell, R. "Balancing work and rest to combat driver fatigue: An investigation Charlton, S.G., and Baas, P.H. "Fatigue and fitness for of two-up driving in Australia." (1997). Accident Analysis duty of New Zealand truck drivers." (1998). Road Safety & Prevention, 29 (4) pp. 54153. Research, Policing, Education Conference. Wellington, This study is the fourth in a series examining driver fatigue New Zealand. Vol. 2. pp. 2149. in the Australian long-distance road transport industry. The effects of driver fatigue have been implicated in a large Thirty-seven long-haul truck drivers were measured on a rou- number of truck crashes and road fatalities in other countries. tine 4,500-km round trip. Two types of driving operations While there are no extensive studies of fatigue-related road were compared, single driving, involving a solo driver, and accidents in New Zealand, the road characteristics and driving two-up driving, where a pair of drivers operate a truck con- environment make any decrease in performance due to driver tinuously and alternate between work and rest. Two-up driv- fatigue a significant potential threat to road safety. This paper ers reported higher levels of fatigue than single drivers describes an on-going Road Safety Trust-sponsored study of overall and tended to show poorer levels of performance. how common driver fatigue is in New Zealand and the degree However, this result appeared to reflect differential fatigue at to which these truck drivers suffer from fatigue related the start of the trip. Both two-up and single drivers showed effects. Using a portable driving simulator installed in a car- marked increase in fatigue across the first half of the trip, fol- avan, volunteer truck drivers are asked to complete a brief lowed by a substantial recovery of alertness and performance survey (about their driving hours and their amount of sleep in provided that drivers had stationary overnight rest at mid trip the past 48 hr, how sleepiness affects them, and the level of or had shorter trips. Fatigue continued to increase on the sec- fatigue they feel at that moment), and go for a "drive" on the ond half of the trip for drivers who did longer trips without driving simulator (measuring their vehicle control and reac- the benefit of a substantial night rest or who did not have tion times) as they stop their trucks at depots, rest stops, and access to on-board rest, that is, single drivers. The use of cargo terminals throughout the day and night. In comparison overnight rest, in combination with two-up driving, appeared with indirect measures of fatigue, such as inspection of driv- to be the most successful strategy for managing fatigue across ing hours in log books, the fitness-for-duty test has obvious the trip. job relevance (measuring actual driving performance) and enjoys a high degree of driver acceptance. Freund, D. and Vespa, S. (1997) "U.S./Canada study of commercial motor vehicle driver fatigue and alertness." FMCSA Tech Brief, 2001 (FMCSA-MCRT-01-006). Proceedings of the XIIIth World Meeting of the Inter- "Impact of local/short-haul operations on driver fatigue: national Road Federation, Toronto, Ontario. June Field study." 1620, 1997. The CMV Driver Fatigue and Alertness Study was the FMCSA Tech Brief, 2000/09 (FMCSA-MCRT-00-015). largest and most comprehensive over-the-road study of its kind "Effects of sleep schedules on commercial motor vehicle ever conducted in North America. Its primary purposes were driver performance--Part 2." to establish measurable relationships between CMV driver activities and physiological and psychological indicators of Federal Motor Carrier Safety Administration. "Impact fatigue and reduced alertness and to provide a scientifically of sleeper berth usage on driver fatigue." (2002). Report valid basis to determine the potential for revisiting the 60-year- Number: FMCSA-RT-02-050. old HOS regulations. Work-related factors thought to influence The goal of this project was to assess the impact that sleeper- the development of fatigue, loss of alertness, and degraded per- berth use has on operator alertness. The participants in this formance in CMV drivers were studied within an operational study were 47 males and 9 females, constituting 13 teams and setting of real-life, revenue-generating trips. These included 30 single drivers. All drivers who participated in the study were the amount of time spent driving during a work period; the recruited from one of four for-hire commercial trucking com- number of consecutive days of driving; the time of day when panies. Two tractors, a 1997 Volvo L4 VN-series tractor and a driving took place; and schedule regularity. It was found that 1995 Peterbilt 379, with functionally identical instrumentation the strongest and most consistent factor influencing driver packages and data collection systems, were used. The data fatigue and alertness was time of day; drowsiness, as observed acquisition system functioned to record four camera views, in video recordings of the driver's face, was markedly greater

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95 during night driving than during daytime driving. The number sonal health status were analyzed from 567 professional driv- of hours of driving (time on task) was not a strong or consis- ers with 5 work descriptions. Of the drivers, 31% had been tent predictor of observed fatigue. Other study findings noted regularly driving more than 10 hr, 19% reported having dozed that the number of driving periods was not a strong or consis- off at least twice while driving, and 8% reported a near- tent fatigue predictor; that there was a low correlation between miss situation due to dozing off during the past 3 months. drivers' subjective self-ratings of alertness/sleepiness and Sleepiness-related problems while driving appeared across concurrent objective performance measures; and that there all driver groups, including drivers transporting dangerous was a large difference between the mount of sleep drivers goods and bus drivers, and were strongly related to pro- reported as their "ideal" and the amount they obtained during longed driving, sleep deficit and drivers' health status. The principal sleep periods in the study setting. While there is no effects of the latter factors were interactive and cumulative: single solution to the fatigue problem, much can be done to Frequent sleepiness-related problems occurred in more than address driver fatigue through a combination of innovative one-half of the drivers with the combination of prolonged driv- HOS regulation and enforcement, education, driver work ing, sleep deficit, and lowered self-perceived health. The scheduling, innovative fatigue management programs, driver results give unreserved support for regulating driving hours screening, fitness for duty and alertness monitoring systems, and increase concern of the connection between professional and additional research. For the covering abstract of this con- drivers' health status and sleepiness-related problems while ference, see IRRD number 872978. driving. Gillberg, M., Kecklund, G., and Akerstedt, T. (1996). Hanowski, R. J., Wierwille, W. W., Gellatly, A. W., Early, "Sleepiness and performance of professional drivers in a N., and Dingus, T. A. (2000). "Impact of local short-haul truck simulator--comparisons between day and night operations on driver fatigue." Department of Trans- driving." Journal of Sleep Research, 5, pp. 1215. portation Federal Motor Carrier Safety Administration. Previous research has shown that night driving perfor- The goal of the Hanowski et al. (2000) study, which mance may be seriously affected by sleepiness. The present examined the impact of the individual differences of truck study compared daytime and nighttime performance of pro- drivers on the occurrence of driving incidents, was to study fessional drivers on a simulated truck driving task. A sec- fatigue experienced by short-haul truck drivers. Forty-two ondary purpose was whether a nap or a rest pause would affect male short-haul drivers (mean age = 31) participated in the performance. Nine professional drivers participated in a coun- study. Drivers completed 2 weeks of MondayFriday day- terbalanced design. The conditions were day driving (DAY- time driving on normal delivery routes that were within 100 mi DRIVE), night driving (NIGHTDRIVE), night driving with a of home. Their distribution of work consisted of driving 30-min rest (NIGHTREST), and night driving with a 30-min (28%), loading/unloading (35%), other assignments (26%), nap (NIGHTNAP). Each condition consisted of three consec- waiting to unload (7%), eating (2%), resting (0.5%) and other utive 30-min periods. For the DAYDRIVE and NIGHT- activities (1.5%). DRIVE, all periods were spent driving while the second A number of measures were used to assess the fatigue, period was either a rest pause or a nap for the other two con- inattention, and drowsiness of the drivers, including analysis ditions. Mean speed, standard deviation of speed, and stan- of a videotape of the 3-min interval preceding the start of a dard deviation for lane position were recorded. Self ratings of critical incident. An incident was defined as a control move- sleepiness were obtained before and after each 30-min period. ment exceeding a threshold based on driver or analyst input. Reaction time tests and 10-min standardized EEG/EOG Analysts recorded eye transitions and the proportion of time recordings were obtained before and after each condition. EEG/EOG recordings were obtained before and after each that the driver's eyes were closed/nearly closed, or off the condition. EEGs/EOGs were also recorded continuously dur- road, during these 3-min intervals. ing driving. The effects on driving were small but significant: The drivers' mean sleep was 6.43 hr per night (sleep log) night driving was slower, with a higher variability of speed, and 5.31 hr based on the actiwatch. Drivers who showed evi- and had higher variability of lane position. Subjective and dence of fatigue and were involved in fatigue-related inci- EEG/EOG sleepiness were clearly higher during the night dents had less sleep and of a poorer quality than drivers who conditions. Reaction time performance was not significantly did not show signs of fatigue. Twenty-one percent of the inci- affected by conditions. Neither the nap nor the rest pause had dents implicated fatigue as a contributor based on observer any effect. assessments of drowsiness and the increase in proportion of time with eyes closed or nearly closed. Hakkanen, H. and Summala, H. (2000). "Driver sleepiness- Over the 2-week period, there were 77 incidents (average related problems, health status, and prolonged driving 1.8 per driver) where the driver was judged to be at fault. With among professional heavy-vehicle drivers." Transporta- respect to individual differences, 10 of the 42 drivers were tion Human Factors, 2(2), 151171. involved in 86% of the incidents. The younger and less expe- Questionnaire data concerning the frequency of prolonged rienced drivers were significantly more likely to be involved in driving, sleepiness-related problems while driving, and per- critical incidents and exhibited higher on the job drowsiness.

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96 The strength of this study is that it focuses on individual in affecting close calls and crashes via hierarchical regres- differences and it has strong face validity with respect to traf- sion. Findings indicate that fatigue-inducing factors inherent fic safety issues. The main weakness from the perspective of in driving work and safety practices accounted for apprecia- our study is that it does not address recovery directly. ble variation in driving fatigue (R sq. = 0.42) and close calls (R sq. = 0.35), but not crash involvement. Driving while Klauer, S.G., Dingus, T.A., Neale, V.L. and Carroll, R.J. fatigued also accounted for incremental increases in the (2003). "The effects of fatigue on driver performance for amount of variation in close calls, after considering inherent single and team long-haul truck drivers." Driving Assess- factors/safety practices. ment 2003--The Second International Driving Sympo- sium on Human Factors in Driver Assessment, Training O'Neill, T.R., Krueger, G.P., Van Hemel, S.B., and and Vehicle Design. Park City, Utah. McGowan, A.L. (1999). "Effects of operating practices on Driver fatigue is an important safety issue for long-haul commercial driver alertness." Rep. No. FHWA-MC-99- truck drivers. To provide an efficient means of obtaining 140, Office of Motor Carrier and Highway Safety, Fed- sleep, long-haul truck drivers often use tractors equipped eral Highway Administration, Washington, D.C. with sleeper-berth units. Depending on the type of cargo and This driving simulator study sought to assess truck driver distances traveled, long-haul truck drivers either drive in fatigue or alertness as affected by non-driving, but on-duty teams or alone as single drivers. Team drivers, therefore, typ- activities, such as loading/unloading a vehicle. It also exam- ically sleep in a moving truck whereas single drivers sleep in ined the effects of driver performance on extended HOS-- a stationary truck. It has been hypothesized that sleeping in a 14 hr on duty/10 hr off duty (12 hr daytime driving, 0700 to moving truck could adversely affect the sleep quality and, 2100). Researchers examined driver performance over a therefore, the alertness level of team drivers. A naturalistic 15-day period. In addition, the amount of nonduty time (rest data collection system was developed and installed in two and recovery) needed to reestablish baseline fitness for duty Class 8 heavy trucks. This trigger-based system consisted of was investigated. vehicle sensors and cameras that allowed the experimenters to obtain the driving performance and driver alertness data O'Neill, T.R., Krueger, G.P., Van Hemel, S.B., McGowan, for analysis of fatigue. Fatigue was measured using both A.L. and Rogers, W.C. (1999) "Effects of cargo loading objective and subjective measures that were recorded before and unloading on truck driver alertness." Transportation and after sleep and while driving. Fatigue and driving per- Research Record 1686, pp. 4248. formance were compared for single versus team drivers to The relationship between physical and mental fatigue is not determine which driver type acquired the greatest sleep deficit well understood or well documented, a lapse that affects under- during a trip. Results suggest that single drivers were more standing of the interaction between loading and unloading activities and safe operation in the trucking industry. This frequently involved in critical incidents while exhibiting experiment addresses the effects of loading and unloading on extreme drowsiness than were team drivers by a factor of driving performance by measuring driving impairment in vol- 4 to 1. These results are discussed in relation to the general unteer truck drivers operating a truck-driving simulator. Ten safety of single versus team truck operations. drivers participated, each for 17 days, including 2 driving weeks of 5 days with 14-hr duty cycles separated by two Mitler, M.M., Miller, J.C., Lipsitz, J.J., Walsh, J.K., and 58-hr rest periods. During one of the driving weeks, partic- Wylie, C.D. (1997). "The sleep of long-haul truck driv- ipants were given a significant hand-loading task, 3 hr of ers." New England Journal of Medicine, 337(11). hand-loading pallets of boxes on 3 of 5 days; during the remaining week, only driving tasks were scheduled. Perfor- Morrow, P.C. and Crum, M.R. (2004) "Antecedents of mance measurement focused on driver responses to planned fatigue, close calls, and crashes among commercial and unplanned crash-likely challenges and vigilance tasks, motor-vehicle drivers." Journal of Safety Research, 35 (1). supported by simulator-mediated driving indicators, such as Minimizing driver fatigue among CMV drivers is a major lane-keeping performance. Measures of subjective drowsi- safety issue in the United States. This paper examines the ness also were maintained. The effects of the loading and effects of potentially fatigue-inducing factors inherent in truck unloading task were mixed. There was an initial improve- driving work and company safety management in explaining ment in alertness, apparently because of the break in activity (1) drivers driving while fatigued, (2) the frequency of close and a period of exercise; however, this effect wore off as the calls due to fatigue, and (3) actual crashes among CMV driv- day progressed and may have contributed to a decrease in ers. Data for this study is derived from a survey of CMV driv- overall performance after 12 to 14 hr of duty. ers in 116 trucking firms, with all data being driver-reported. The relative roles of fatigue-inducing factors and safety man- O'Neill, T. R., Krueger, G. P., Van Hemel, S. B., and agement practices in explaining variation in fatigue, close McGowan, A. L. (1999). "Effects of operating practices calls, and crashes are reported, along with the roles of fatigue on commercial driver alertness." Rep. No. FHWA-MC-

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97 99-140, Office of Motor Carrier and Highway Safety, increase in cognitive errors, that is, lapses in vigilance lead- Federal Highway Administration, Washington, D.C. ing to missed turns. The goal of the O'Neill et al. (1999) study was to assess the Over the driving week, there was a slight but statistically effects of operating practices, namely schedule, loading and significant deterioration in subjective sleepiness, reaction time recovery, on alertness. Ten male CMV drivers participated in response, and measures of driving performance over each 1 week of driving operations in a simulator followed by 58 hr working day. However, driver response in crash-likely situa- of recovery time. This was followed by another week of driv- tions did not show cumulative deterioration. The schedule of ing, 58 hr of recovery time and a final driving day to verify 14 hr on duty/10 hr off duty (12 hr driving) for a 5-day week performance after recovery. Half of the drivers performed did not appear to produce significant cumulative fatigue over 3 days of loading in the first week (i.e., 2 1.5-hr sessions) the 2-week testing period. and had no loading in the second week. The remaining driv- The drivers returned to baseline levels of reaction time, driv- ers did the reverse (i.e., loaded in week 2). On loading days, ing simulator performance, and alertness within 24 hr of drivers performed two 90-min loading/unloading sessions recovery time after the end of a driving week as shown by during the driving day, one in the morning, and one in the sleep latency, reaction time testing, and driver rating of sub- afternoon. The drivers worked 14 hr on duty (i.e., 12 hr driv- jective sleepiness. However, it should be noted that drivers ing plus scheduled breaks) beginning at 0700, followed by lived in an apartment during testing; therefore, sleep may not 10 hr off duty. have been typical of normal conditions during recovery, Measures of sleepiness, sleep length, psychomotor perfor- where drivers must deal with family and social obligations mance, and driving simulator performance were collected. The which may result in reduced sleep. sleep measures included the Stanford sleepiness scale, self- alertness scales and wrist actigraphs (i.e., sleep length). Mea- Rogers, W. (2000). "Effects of operating practices on sures were collected using the PVT, which has been shown in commercial driver alertness." Proceeding of the Confer- previous studies to be very sensitive to sleepiness. The PVT is ence Traffic Safety on Two Continents held in Malmo, a 10-min period of reaction time performance where drivers Sweden, September 2022, 1999. respond as fast as possible to brief visual stimuli. Reaction time The aim of the study presented was to assess the effects of and lapses (reaction times exceeding 500 m/sec) are recorded. lorry driver loading or unloading on subsequent driver alert- Driving simulator performance measures included lane posi- ness and to measure and document lorry drivers' performance tion, speed maintenance, and shifting performance. Response on a 14 hr on (with 12 hr driving)/10 hr off daytime schedule probes (e.g., tire blowout, merge squeeze, fog, etc.) were used coupled with a weekend recovery process over a 58-hr off- and driver response was evaluated by expert trainers on a duty period between two successive weeks of simulated driv- three-point scale. Probes provided tests of driver vigilance, ing. Measurements of probe performance, cognitive errors, alertness, and response time. lane performance and gear performance were carried out. Individual differences in performance in relation to age Sleep patterns, sleep latency and subjective sleepiness were and height/weight were assessed. The age of the drivers was also measured in order to assess the effect of the rest and correlated with lane (r = 0.508, p < 0.01) and shifting perfor- recovery required to re-establish alertness and fitness for mance (r = -0.287, p < 0.01). Drivers height/weight ratio (a duty. For the covering abstract of the conference, see ITRD surrogate measure for general fitness) was correlated with E204692. poorer lane performance (r = -0.358, p < 0.001) and shifting performance (r = -0.428, p < 0.001). Tech Brief (1999) (FHWA-MCRT-99-008) "Effects of Overall, there was a gradual decline in driver response operating practices on commercial driver alertness." quality, as measured by response probes, with hours of driv- ing. There were improvements after each break, regardless Williamson, A., Feyer, A.M., Friswell, R., and Finlay- of whether it was a rest, meal, or loading activity. After 6.5 hr Brown, S. (2000). "Demonstration project for fatigue of driving, drivers were returned to starting levels of safety management programs in the road transport industry: (as measured by response to probes) by a 45-min lunch break. Summary of findings." The ability to maintain speed within posted limits and gear This document is the final summary of a series of three shifting performance deteriorated somewhat during the latter reports of a project on the development of model work-rest part of the driving day but there was no consistent linear rela- schedules that have demonstrated effectiveness for managing tion to hours of driving. driver fatigue in the long distance road transport industry. There was an improvement in driver response to crash- The purpose of these studies was to help the industry in likely simulated situations after the morning physical activ- designing work-rest schedules to provide additional flexibil- ity. However, gear shifting increased, indicating inefficiency ity for companies and drivers to meet their operational needs in attention and co-ordination, and there was greater lane posi- but also manage fatigue most effectively. The report provides tion variability after the morning loading session. The only an overview of the findings of each of the three studies. The effect of the afternoon loading session appeared to be an first study developed a set of fatigue-sensitive performance

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98 measures and alcohol-equivalent standards for each of them. Similar to the short-haul drivers, the majority of long-haul The results also demonstrated sleep deprivation of 17 hr or drivers' first sleep bouts were initiated between 2200 and more produced decrements in performance capacity equivalent 0359. However, long-haul drivers initiated their first sleep to the community-accepted standard of 0.05% BAC. They also bouts more frequently during 0000 and 0359. The duration of showed that long distance drivers appeared to cope with the long-haul drivers' first sleep bouts clustered between 6 and demands of sleep deprivation better than non-professional driv- 10 hr in duration. Sleep bouts exceeding 10 hr in duration ers. The second and third reports detailed the evaluation of were uncommon and none exceeded 12 hr. Some sleep bouts four work-rest schedules, two of which complied with the were initiated in the early and late afternoon hours (1200 to current working hours regulations and two were alternative 1959) and, unlike short-haul drivers, almost half of the first schedules that did not comply with the regulations. The eval- sleep bouts initiated during this time frame were longer than uations were carried out on the road while drivers were doing 4 hr in duration. their normal trips. The exception was one of the alternative There were large day-to-day variations in total sleep time compliance schedule evaluations which were done with pro- for drivers in both groups. Sleep times varied for some long- fessional long distance drivers in a simulation mode rather and short-haul drivers by up to 11.2 hr across the 20 study than on-road. The results of the regulated hours evaluations days for the long- and short-haul drivers. Other drivers main- showed that as long as drivers were rested before their trips, tained more consistent sleep/wake schedules. Some drivers the regulated regime produced increased fatigue and pro- showed a pattern that suggested chronic sleep restriction with duced some performance decrements at the end of a work intermittent bouts of extended recovery sleep. The authors period between long 24-hr breaks. The level of effect was not believed that this suggested that although work-rest sched- significantly high however, relative to alcohol-equivalent ules can be devised to help minimize CMV driver sleep debt, standards. In contrast, the alternative compliance schedule optimal enhancement of driver alertness and performance evaluations demonstrated that it is possible to introduce flex- will require additional and imaginative approaches. ibility in scheduling such as by extending the length of work The strength of this study is that all periods of sleep, not periods, but only if an adequate balance is maintained between just those taken off duty, were recorded for a large group of work and rest. CMV drivers over an extended period of time. The main lim- itation as far as this study is concerned is that the issue of Williamson, A., Feyer, A., and Friswell, R. (1996). "The recovery was not addressed specifically. impact of work practices on fatigue in long distance truck drivers." Accident Analysis & Prevention, Vol. 28, No. 6, Wylie, C.D. "Driver drowsiness, length of prior principal 709719. sleep periods, and naps." (1998). Transportation Devel- Both long- and short-haul drivers averaged approximately opment Centre. Report No. TP 13237E. 7.5 hr of sleep per night, which is within normal limits for The purpose of this study was to assess the relationships adults. However, in contrast to short-haul drivers who only between prevalence of driver drowsiness observed on a trip, obtained 3% of their sleep during on-duty periods, long-haul length of prior principal sleep periods, and naps taken during drivers obtained 44% of their sleep during on-duty periods. the trip, based on the data collected from actual revenue runs Short-haul drivers were more likely to consolidate their daily of the Driver Fatigue and Alertness Study (DFAS) and the sleep into a single sleep period. As long-haul drivers obtained Commercial Motor Vehicle Driver Rest Periods and Recov- almost half of their daily sleep during work-shift hours (mainly ery of Performance Study. A rhythmic time of day variation sleep-berth time), it appears that they spend a significant por- was the strongest influence found on drowsiness, followed by tion of the work shift in a state of partial sleep deprivation, length of the last main sleep. A mathematical model was until the opportunity to obtain recovery sleep on duty pre- developed that describes these effects. It was found that half sents itself. the naps studied were taken in apparent absence of drowsi- There was no off-duty duration that guaranteed adequate ness, and half appeared to be taken in response to sudden sleep for the long- or short-haul drivers. As drivers likely use increases in drowsiness. Naps in trips with judged drowsiness a substantial portion of their off-duty time to attend to per- appeared to result in a recovery effect, compared with the rel- sonal business, off-duty time must be of sufficient duration to atively high levels of drowsiness seen in the hour prior to allow drivers to accomplish these tasks and to obtain suffi- napping. However, drowsiness remained substantially ele- cient sleep. This may be particularly important for long-haul vated for 2 hr after napping. drivers, who often did not sleep at all during off-duty periods. The bulk of the first (main) daily sleep bouts for short-haul Wylie, C.D., Shultz, T., Miller, J.C., and Mitler, M.M. drivers were initiated between 2000 and 0200. Sleep bouts (1997). "Commercial motor vehicle driver rest periods initiated at these times lasted longer (i.e., clustered between and recovery of performance." 6 and 10 hr) than sleep bouts initiated at other times of day. The purpose of this study was to assess the "recovery" Several of the sleep bouts initiated between these times lasted effect of 0, 1, and 2 workdays off on driver fatigue and alert- longer than 12 hr. ness. It was hypothesized that there would be some level of