As part of a new Hours of Service Rule published in December, 2011 by the Federal Motor Carrier Safety Administration (FMCSA), truck drivers are now required to have at least two nighttime periods in their 34-hour break to “restart” their hours of service week.  When Congress passed the new Moving Ahead for Progress in the 21st Century Act (MAP-21), a request to undertake a naturalistic field study of this new rule was asked of the FMCSA.  Previously, two laboratories studies had been conducted regarding this new rule.  The naturalistic field study’s results (click here to read “Field Study on the Efficacy of the New Restart Provision for Hours of Service”) were published in January, 2014.

The study’s authors indicate that the results of the study show that “having at least two nighttime periods from 1 a.m. until 5 a.m. in the restart break helps to mitigate fatigue.  These results are consistent with earlier, laboratory-based studies of the restart break, and constitute further evidence in support of the efficacy of the new restart rule.  Given that driver fatigue has been documented to be a risk factor for truck crashes, the new restart rule can thus be expected to help improve safety on U.S. roads.”

What the New Rule Mandatesbanner

Truck driver’s hours of service are limited by the Federal Motor Carrier Safety Regulations (FMCSRs).  A driver may not continue to drive after being on-duty for 60 hours in the most recent 7 day period or 70 hours in the most recent 8 day period.  Previously, the optional restart provision, also known as the 34-hour restart rule, provided that drivers could restart this on-duty schedule after taking a break for at least 34-hours consecutively to recuperate.  The break was intended to mitigate the build-up of fatigue across duty cycles.

The current rule, which went into effect on July 1, 2013, has altered this requirement.  Now, if a driver wishes to use the “restart” rule, he or she must take a break for at least 34 consecutive hours including at least two nighttime periods, which is defined as 1 a.m. to 5 a.m.  The rule goes on to state that the 1 a.m. to 5 a.m. period is based upon the driver’s home terminal time zone.

The Studies

Previously, two laboratory studies had been conducted regarding this new restart rule to determine if it would be effective at reducing fatigue in truck drivers.  The two laboratory studies set out to determine the efficacy of the 34-hour restart rule in daytime vs. nighttime duty schedules.  The studies were conducted from 2008 through 2010.

The two studies provided some evidence that in comparison to the daytime duty schedule driver, a nighttime duty schedule driver had decreased amounts of sleep, increased subjective sleepiness and lower performance on a range of objective performance tasks.  When evaluating the effects of extending the restart break to include two nighttime periods vs. just one nighttime period, the studies found that the effects of fatigue build-up were mitigated when drivers had the second nighttime period to recuperate.  The studies concluded that drivers could see an improvement in fatigue levels by extending the 34-hour restart rule to include two nighttime periods.

Truck imageIn order to determine if this same efficacy would be seen in real-world applications, the FMCSA undertook to have a field study conducted by researchers at the Sleep and Performance Research Center.  The field study’s authors intended the study to measure sleep, reaction time performance, sleepiness and driving performance across two duty cycles and the intervening restart break.  Initially, the study had 119 participants voluntarily sign up.  Ultimately, the data from 106 drivers was evaluated with over 1,800,000 one-minute data points used for analysis.  By this standard, this was among the largest studies of its kind.

The field study was completed between January and June, 2013.  Participation by the drivers required the driver to have a valid commercial motor vehicle driver’s license, be fit for duty by regulatory standards, be representative of the drivers affected by the maximum driving time requirements and have planned to take a restart break immediately before as well as during the study participation period.  The study participants ranged in age from 24 to 69 years old with driving experience of less than one year through 39 years.  100 men and 6 women participated.  The drivers were given smartphones and wrist bands to track certain information and to take attentiveness tests.  In addition, the drivers were provided specific trucks with equipment installed that tracked certain driving actions.  Ultimately, only the most reliable data was used and evaluated as part of the results.

Fatigue Outcomes

The primary outcome used to evaluate a driver’s fatigue was the number of lapses in attention on a 3 minute psychomotor vigilance test (PVT).  This test has been shown to be among the most sensitive outcome metrics with the most favorable statistical properties for measuring fatigue.  The study found that drivers who took the test after a restart break with only one nighttime period had 2 lapses in attention per test taken.  But, the drivers who took the test after a restart break with two nighttime periods had 1.7 lapses in attention per test taken.  The authors of the study note that “the magnitude of this difference [1.7 vs. 2.0 lapses] is comparable to the daily increase in lapses of attention on the 3-minute PVT that has been observed in a study involving sleep restriction to 4 hours per day.”

graphThe lapses in attention are reaction times of 355 ms or longer.  At 60 miles per hour, a truck driver who has a lapse in attention of 355 ms would travel 30 feet or more.  Research shows that as drivers experience more lapses in attention, the duration of each lapse in attention becomes longer.

A secondary fatigue outcome that was evaluated was driving performance.  This was measured in terms of lane deviations during the two duty cycles of each driver during the study.  The results of the driving performance measurements were consistent with the effect seen on lapses of attention in the PVT.  The authors go on to note though that the effect of the new 34-hour restart rule on lane deviations remains to be determined.

What the Study Says About the New Hours of Service Rule

“A running theme in sleep and fatigue research across modes of transportation, in other industries, and in the military is that of duty schedules causing temporal conflict with the neurobiology of circadian (i.e., 24-hour) rhythms and sleep regulation, resulting in sleep curtailment and fatigue.  This highlights the criticality of both the timing and duration of off-duty periods for sleep recuperation such as restart breaks, as has also been shown in the laboratory.”  This study confirms that the new rule increases the recuperative sleep potential during the restart breaks and as a result mitigates driver’s fatigue.

Ultimately, the field study findings were consistent with the findings of the two laboratory studies previously completed to determine the efficacy of the new 34-hour restart rule.  The improvements in the results on the fatigue outcome tests indicate that a second nighttime period being included in the 34-hour break has a positive effect on driver’s attention and fatigue levels.  “The extra sleep opportunity offered by the second biological night appeared to be responsible for this improvement.”