FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION

FMCSA Contact: Martin Walker (MC-RRR) 202-385-2364

Duration Restart Period Needed

to Recycle with Optimal

Performance: Phase II

The objective of this Phase II project was to determine whether a restart period

involving two biological nights of sleep would be more effective in restoring

performance in individuals working night shifts under the hours of service (HOS)

regulations governing property-carrying commercial motor vehicle (CMV) drivers

than the current 34-hour restart provision. Building on the Phase I project, which

evaluated the 34-hour restart using two groups of drivers, one operating in daylight

and one at night, this new study with nocturnal duty periods and a restart period

that includes two biological nights was undertaken using a within-subjects inlaboratory experimental study design with testing of cognitive performance task

and high-fidelity driving simulator performance.

BACKGROUND

The current Federal Motor Carrier Safety Administration HOS regulations for

property-carrying CMV drivers prescribe that drivers: 1) may drive 11 hours in a

14-hour window after coming on duty following 10 consecutive hours off duty; 2)

may not drive after 60/70 hours on duty in 7/8 consecutive days; and 3) may restart

a 7/8 consecutive day period after taking 34 or more consecutive hours off duty

(the 34-hour restart rule). However, the 34-hour restart rule only partially addresses

circadian rhythms in both performance and sleep propensity.

The Phase I research project showed that while the 34-hour restart was effective at

maintaining performance during daytime duty periods, it was generally not

effective at maintaining performance in individuals scheduled to be awake during

the night. The primary outcome variable was performance on the well-validated,

10-minute psychomotor vigilance test (PVT), which was administered eight times

per duty period. Subjects were randomized to one of two study conditions. In the

“best case” condition involving daytime duty periods, PVT performance was

statistically indistinguishable during the “week” (5 days with 14 duty hours per

day) before and after a 34-hour restart period. In contrast, in the “worst case”

condition involving nighttime duty periods, PVT performance was significantly

degraded during the “week” after the 34-hour restart period.

The total duration of the sleep opportunities in the 34-hour restart period was the

same for the “worst case” condition as for the “best case” condition. However, the

34-hour restart period in the “worst case” condition included only one biological

night (i.e., nocturnally placed sleep opportunity), whereas the 34-hour restart

period in the “best case” condition included two biological nights.

MeThODOlOGy

A sample of 12 healthy male subjects was studied in a within-subjects comparison

of two 5-day work periods separated by a restart period containing two biological

nights. The two 5-day work periods entailed nighttime wakefulness and work (14-

hour/day) and daytime sleep. The restart break involved temporarily transitioning

back to a daytime schedule.

U.S. Department of Transportation

Federal Motor Carrier Safety Administration

T e c h B r i e f

Office of Analysis, Research and

Technology

1200 New Jersey Ave. SE

Washington, DC 20590

Programs of the Federal Motor Carrier

Safety Administration (FMCSA)

encompass a range of issues and

disciplines related to motor carrier

safety and security. FMCSA’s Office of

Analysis, Research and Technology

defines a “research program” as any

systematic study directed toward fuller

scientific discovery, knowledge, or

understanding that will improve safety,

and reduce the number and severity of

commercial motor vehicle crashes.

Similarly, a “technology program” is a

program that adopts, develops, tests,

and/or deploys innovative driver and/or

vehicle best safety practices and

technologies that will improve safety

and reduce the number and severity of

commercial motor vehicle crashes. An

“analysis program” is defined as

economic and environmental analyses

done for agency rulemakings, as well

as program effectiveness studies,

state-reported data quality initiatives,

and special crash and other motor

carrier safety performance-related

analyses. A “large truck” is any truck

with a Gross Vehicle Weight rating or

Gross Combination Weight rating of

more than 10,000 pounds.

Currently, the FMCSA Office of

Analysis, Research and Technology is

conducting programs in order to

produce safer drivers, improve safety

of commercial motor vehicles, produce

safer carriers, advance safety through

information-based initiatives, and

improve security through safety

initiatives. The study described in this

Tech Brief was designed and

developed to support the strategic

objective to produce safer drivers. The

primary goals of this initiative are to

ensure that commercial drivers are

physically qualified, trained to perform

safely, and mentally alert.
The main goal of the study was to evaluate whether the two-night restart period was effective at

maintaining performance. To this end, performance on a variety of cognitive performance tasks

and on a high-fidelity driving simulator was measured throughout the study. The primary

performance outcome measure was the number of lapses (reaction times greater than 500

milliseconds) on a 10-minute PVT.

Average PVT performance in the 5-day work period after the restart break was not significantly

different from that in the 5-day work period before the restart break, indicating that the two-night

restart period was effective at maintaining performance. However, there was a transient, modest

degradation of performance on the day immediately following the two-night restart period.

Further, the restart period was only partially effective with respect to other outcome measures,

including lane deviation in a high-fidelity driving simulator.

Secondary analyses compared the study results to the effects of a 34-hour restart period as

examined previously in the Phase I research project. These analyses indicated that, in the context

of nighttime wake/work schedules, the inclusion of two nights in the restart break was an

improvement over the 34-hour duration across a range of outcome measures. The extra sleep

opportunity (i.e., second biological night) associated with the restart period appeared to be

responsible for this improvement.

Key fINDINGs

This Phase II study followed up on the findings of Phase I, which revealed that the effectiveness

of the 34-hour restart provision in the HOS regulations depends on circadian timing. Specifically,

the Phase I study revealed that 34 hours off duty was insufficient to restore performance for a 5-

day work schedule involving nighttime wakefulness (and daytime sleep), while transitioning back

to a daytime schedule during the restart period. The present Phase II study investigated whether

for such a schedule, extending the restart period by 24 hours, to include an additional biological

night, would result in greater recuperation. In keeping with the experimental procedures

established in Phase I, an in-residence laboratory research study was conducted in Phase II to

examine the effects of the two-night restart, using the results of Phase I for reference.

The effectiveness of the restart period containing two biological nights in maintaining performance

overall across the two 5-day work periods does not imply that there were no performance deficits

during these nocturnal work periods. In agreement with key principles of sleep/wake physiology,

PVT performance deteriorated during each nighttime waking period. However, the level of

nocturnal performance deterioration was not significantly greater after the 58-hour restart period

that the study used than before. This is in contrast with the 34-hour restart period examined in

Phase I, which was not as effective at preserving performance across two 5-day nighttime work

periods. As such, extending the restart period from 34 hours to 58 hours constituted an

improvement with regard to the effectiveness of the restart period in the context of working nights.

Important for the interpretation of the findings from the Phase II study is the fact that transition

sleep opportunities were scheduled as part of the revised restart period. These essentially served as

prophylactic naps, which are known to be effective countermeasures for cognitive performance

impairment. It is possible that without such strategic napping, performance following the restart

period would have shown increasing deficits. It should also be noted that the research subjects

were carefully screened healthy young males. Had the researchers studied a sample with sleep

apnea or other medical conditions, the expected performance deficits would have been greater.

It should be noted that the driving simulator scenarios (roads, routes, events, conditions, etc.) were

standardized, with randomized pedestrian/dog crossing events, across the driving performance

time points of the Phase II study (using the same scenarios as employed in Phase I). The scenarios

did not control for the lower traffic density or reduced visibility typically associated with

nighttime driving. As such, the driving simulator findings should be interpreted as indicative of

basal capability for driving rather than actual driving performance in the real world. Further

research is needed to study the effectiveness of the tested restart break in terms of real-world

driving performance, safety, and cost.
December 2010

Publication Number:

fMCsA-RRR-10-062-TB

CONClUsIONs

The study data showed no significant difference in PVT lapses between the prerestart and post-restart work periods overall, indicating that a restart period that

includes two nights was effective at maintaining performance. Thus, the null

hypothesis that the tested restart period would be effective at maintaining

performance was not rejected.

A caveat to this finding is that there was a transient, modest degradation of

performance on the day immediately following the restart period. This effect

was not seen in Phase I following the 34-hour restart period, suggesting that the

increased effectiveness of the two-night restart period for nighttime work

schedules comes at the cost of minor difficulty to re-adjust to a nighttime

schedule after the daytime-oriented restart break. If a nighttime wake schedule

were to be maintained during the two-night restart period, it is possible that

gradual circadian adjustment would have occurred, potentially eliminating the

post-restart transient performance degradation. The real-world utility of this

possibility is questionable, though, as it is improbable that many individuals

would elect to maintain a permanent night shift schedule if given the choice.

Objective performance and subjective sleepiness and mood outcomes varied in

the extent to which they were preserved during the experimental 5-day nocturnal

work period following the restart break. Thus, whereas the tested restart break

was more effective at maintaining waking function than the 34-hour duration

previously studied in Phase I, whether the effectiveness was sufficient depended

on which outcome measure was considered. For lane deviation during simulated

driving, which may have been the most operationally relevant outcome measure

in this laboratory study, the two-night restart break was not fully effective as

compared to the daytime work condition studied previously in Phase I.

However, whether increasing the duration of the restart period even more would

make a substantive difference is not certain, as circadian factors may prevent

further improvement in nighttime work schedules.

The research subjects in this study were healthy young adults with no sleep

disorders, and their scheduled sleep times were protected from outside

interruptions. However, sleep apnea and other medical conditions are common

among CMV drivers. Furthermore, drivers may experience logistical difficulties

protecting time to sleep because of family and other responsibilities; and they

may obtain less or degraded sleep when sleeping in a sleeper berth or in

unfamiliar environments. Nevertheless, it would still be expected to hold that a

two-night recovery period entails a relative improvement over 34 hours for the

duration of the restart period in the context of nighttime operations. That said,

validation of the study findings in a sample of CMV drivers in a real-world field

study is important.

Although this study specifically examined the effectiveness of a 58-hour restart

period, it is important to note that the restart period included two biological

nights of sleep. Given what is currently known about sleep, circadian rhythms

and cognitive performance, it is clear that the observed benefits of the 58-hour

restart period (relative to 34 hours) were not simply a function of having

increased time off. Rather, they were due to the fact that the 58-hour restart

allowed for two sleep periods with circadian timing conducive for sleep (i.e.,

nighttime on the biological clock). Therefore, when considering the findings of

this study in operational scheduling practices, the restart period does not

necessarily need to be 58 hours in duration—the critical factor is that the restart

period should include two opportunities for sleep during biological night. The

study findings highlight the importance of considering the principles of

sleep/wake physiology and circadian effects on fatigue and performance in HOS

regulations.

Full report title:

Duration of Restart Period Needed

to Recycle with Optimal

Performance: Phase II (Report No.

FMCSA-RRR-10-062)

Authored by:

Hans P.A. Van Dongen, Ph.D.,

Melinda L. Jackson, Ph.D., and

Gregory Belenky, Ph.D.

Performing Organization:

Sleep and Performance Research

Center, Washington State

University, Spokane, WA 99210

Key Words:

circadian rythym, CMV, commercial

motor vehicle,HOS, hours of

service, restart, sleep, sleepiness

Notice:

Tech Briefs are disseminated under

the sponsorship of the U.S.

Department of Transportation

(USDOT) in the interest of

information exchange. Tech Briefs

provide a synopsis of the study’s

final publication. Tech Briefs do not

establish policies or regulations, nor

do they imply USDOT endorsement

of the conclusions or

recommendations. The U.S.

Government assumes no liability

for its contents or their use.

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Briefs may be accessed at

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