The hours-of-service proposed rule is based on a large body of sound research dealing with work, fatigue, alertness, sleep cycles and related matters. The FMCSA reviewed nearly 150 research studies and other documents, many of which were submitted or referred to by docket commenters. Many of the reviewed documents reported on research conducted on motor carriers and CMV drivers. Others, such as studies on shiftwork, sleep and performance, and the physiological nature of sleep, were relevant to the issue of CMV driver safety.

The studies underlying this proposed rule make the point that adverse effects of sleep deprivation can occur when the opportunity to take sleep is curtailed, when people try to obtain sleep during periods of the day when their systems are in a more active physiological state (such as mid-morning and early evening), or when environmental conditions are not conducive to obtaining sleep. Adverse effects include slower reaction times, poor and variable responses, deterioration of judgment, less vigilance and attention, and loss of alertness. Lack of sleep can also produce subjective feelings of tiredness, loss of motivation, and deterioration of mood.

It has been well established that the hours of the day and night are not equivalent from the perspective of human alertness and safe, efficient, and productive performance of workplace tasks. Humans are biologically programmed to operate on a daily cycle of just over 24 hours. If people suddenly shift their wake-sleep cycles (e.g., when traveling across time zones), they must adjust to the new ones and become re-synchronized. This takes about one day per time zone crossed.

Many work environments must be staffed on a 24-hour basis, so workers are scheduled in shifts. Shiftwork can introduce another problem. A nightshift worker, required to sleep during periods of higher physiological activity and to be awake during periods of lower activity, may have difficulty adjusting to an inverted wake-sleep schedule and can accumulate a sleep debt that can seriously affect the level of performance and safety. Even when a consistent schedule is established and wake-sleep patterns are stabilized, it is generally recognized that physiological and performance levels reach the low point of their cycles in the hours after midnight and in the early to mid-afternoon. Therefore, night workers are most susceptible to the dual predicament mentioned above. Unless the night shift worker is able to obtain sufficient restorative sleep on a regular basis, the risk of substandard and potentially unsafe performance substantially increases.

Daily sleep. Each driver should have an opportunity for eight consecutive hours of uninterrupted sleep every day. The current rules require a minimum of eight consecutive hours off. Many drivers do not get more than the minimum 8 hours off duty, although the present regulations certainly allow it. These drivers may have to commute home (or find a place to park), eat, bathe, get physical exercise, and conduct other personal activities, all within their 8-hour off-duty period.

To afford the driver an opportunity to obtain a minimum period of 8 hours to sleep, the research shows that the off-duty periods need to be increased. Docket comments and research strongly suggest the need for total off-duty periods from 10 to 16 hours. Studies in the U.S., Canada, Australia, and Europe have found that the amount of sleep obtained by CMV drivers is variable and often shorter than 8 hours.

The time when sleep is taken is important as well because sleep fragmentation can be a by-product of the timing or the quality of the sleep environment. Daytime sleep also tends to be distinctly shorter than night sleep -- and a single night of sleep is generally insufficient to "pay back" the accumulated sleep debt.

Weekly sleep. For weekly off-duty periods, the research indicates that to negate the effect of accumulated week-long sleep deprivation and restore alertness it is necessary to have at least two consecutive nights off-duty that include the periods from midnight to 6:00 a.m. For long-haul CMV drivers, this period should be up to 56 hours long, but could be reduced to 32 hours as long as that period included two nights covering two periods from midnight to 6:00 a.m. The research suggests that drivers may need even more nights off duty if they have a severe sleep deficit.

The research suggests that performance degrades and crash risk increases markedly after the 12th hour of any duty time during a work shift. Some recent research has suggested that naps can improve performance later in work cycles.

Considerable research suggests there is a higher risk of fatigue-induced single-vehicle accidents at night, especially between midnight and 6:00 a.m. One study reported that crashes at night tend to be more severe, with about 435 injuries per 1,000 crashes between midnight and 6:00 a.m., compared with 320 for the remainder of the day. There are about three times as many fatalities per 1,000 crashes from midnight to 6:00 a.m. Using exposure data classifying night as 9:00 p.m. to 6:00 a.m., truck travel during that period is associated with a relative risk about twice that of the rest of the day.

While drivers who drive to the maximum number of hours allowed and rest to the minimum number of hours required by the HOS rules may be fatigued, the situation of drivers who are not in compliance is undeniably worse. Whatever the limitations of, for example, 5 to 6 hours of interrupted sleep, it is clearly more restorative than little or no sleep.

Unfortunately, many drivers violate the HOS regulations. A recent survey reported the average number of hours reported worked exceeded 63 in the previous 7 days. Twenty-five percent of drivers reported working at least 75 hours in the preceding 7 days and 10 percent reported working more than 90 hours.

Studies germane to this NPRM and relied upon by the FMCSA are discussed in An Annotated Literature Review Relating to Proposed Revisions to the Hours-of-Service Regulation for Commercial Motor Vehicle Drivers, Freund, D.M., Office of Motor Carrier Safety, November 1999, Publication No. DOT-MC-99-129. That review, as well as a copy of each research study it discusses, has been placed in the docket.