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92 SUMMARY OF FINDINGS OF LITERATURE Time of day is far more important that hours of driving in predicting observed fatigue. The review of sources from the period 1996 onward sup- Time of day was far more important than hours of ports evidence in previous findings as follows: driving (time on task) or cumulative number of trips in predicting fatigue (Wylie et al. 1998). Falling asleep at the wheel is a common experience for truck drivers. Sources dating from 1996 onward contain new findings as In a study of 567 drivers, almost one-fifth reported follows: falling asleep at the wheel twice in the last 3 months (Hakkanen and Summala 2000). These are self-reports; Under ideal circumstances, long daytime hours with good the reality is likely to be more. sleep are not a problem. Night driving is associated with poor sleep. In a laboratory study, performance in the 7 and 9 hr Of 4 schedules, drivers in the 13-hr night driving con- time in bed groups was often indistinguishable and dition had the least sleep (3.9 hr total) (Wylie et al. 1998). improved throughout the study. With 7 hr time in bed, Night driving is associated with more falling asleep impaired performance was only found on the more sen- incidents. sitive tasks. When sleep was restricted to 8 hr time in Of episodes of drowsiness during on-road driving, 82% bed during recovery, performance of the group who had occurred between 1900 and 0659 (Wylie et al. 1998). received 9 hr time in bed was slightly worse (Balkin et al. Long-haul drivers get poor sleep. 2000). In a second laboratory study, the schedule of 14 hr A comparison of long-haul and short-haul drivers on duty/10 hr off duty for a 5-day week did not appear found both obtained 7.5 hr sleep on average. However, to produce significant cumulative fatigue (O'Neill et al. long-haul drivers obtained 44% of their sleep during 1999). However, subjects slept in an apartment and may work-shift hours, suggesting that they spend a signifi- not have been subject to normal home distractions, cant portion of the work shift in a state of partial sleep resulting in more sleep than usual. deprivation. (Balkin et al. 2000). Night sleep is important for recovery from a single day Night driving is associated with poorer driving of driving and from several days of driving. performance. A dramatic recovery with respect to fatigue was found Lowered performance was found for drives of 1.5 hr in team drivers who stopped overnight in the middle of in a simulator (Gilberg et al. 1996), and for nighttime a 4- to 5-day trip (Feyer et al. 1997). A small study that on-road driving typical of trucking schedules (Wylie examined 0-hr, 36-hr, and 60-hr recovery found that only et al. 1998). partial recovery occurs after a 36-hr reset for both day Reduced sleep at night is associated with poorer daytime and night drivers (Wylie et al. 1998). performance and with inadequate recovery. Single drivers were more involved in incidents than team A laboratory study of the effects of restricted night drivers. sleep on daytime simulator performance showed that In an on-road study, single drivers were involved in reduced sleep is associated with poorer performance and four times more instances of very/extremely drowsy that recovery to baseline requires more than 1 night of observer ratings than were team drivers and were more 8-hr sleep for those with 3, 5 or 7 hr in bed during the likely to push themselves when they were very tired work week. For the 3-hr group, even 3 recovery nights (Dingus et al. 2001). of 8-hr sleep is not sufficient (Balkin et al. 2000). Insufficient recovery is related to close calls. Dangerous events are related to sleep deficit and pro- Fatigue-inducing factors, especially insufficient recov- longed driving. ery, are statistically associated with a driver experienc- In an on-road study, 20% of 1,249 drivers with less ing fatigue and close calls due to fatigue (Morrow and than 6 hr sleep had 40% of the critical incidents Crum 2004). (Arnold et al. 1997). Frequent sleepiness-related prob- Starting the work week feeling fatigued is a common lems occurred in one-half of drivers who reported a com- experience for CMV drivers. bination of sleep deficit, prolonged driving, and lower Almost half of CMV drivers indicated that they started self-perceived health (Hakkanen and Summala 2000). a new "work week" feeling tired more than "rarely" Driving while fatigued increases likelihood of close calls. (Morrow and Crum 2004). In a study of team versus Driving while fatigued resulted in an increase in the single drivers, team drivers started the week tired (Feyer variation in close calls, after inherent factors and safety et al. 1997). practices were controlled for (Morrow and Crum 2004). Dangerous events related to drivers' self-perceived health Drivers involved in critical incidents were younger and status. less experienced and more likely to exhibit on the job With respect to health, there were increased odds of drowsiness (Hanowski et al. 2000). drivers having more frequent difficulties in remaining