U.S. Department of Transportation

Federal Motor Carrier Safety Administration

FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION

FMCSA Contact: Albert Alvarez (MC-RRR) 202-385-2364

Investigation into Motor Carrier Practices to

Achieve Optimal Commercial Motor Vehicle

Driver Performance: Phase I

Background

The current Federal Motor Carrier Safety Administration (FMCSA) hours of

service (HOS) regulations for freight-carrying commercial motor vehicle

(CMV) drivers prescribe that drivers:

u May drive 11 hours within a 14-hour window after coming on duty

following 10 consecutive hours off duty.

u May not drive after 60/70 hours on duty in 7/8 consecutive days.

u May restart a 60/70-hour period after taking 34 or more consecutive

hours off duty (the 34-hour restart provision).

The scientific evidence supporting the 34-hour restart rule is limited, and the

rule may present problems in light of the current state of sleep science.

Specifically, the rule does not take into account the well-described circadian

rhythms in both performance and sleep propensity.

Depending on circadian placement of both the sleep opportunity and the period

of on-duty time, the current restart provision may be (in the case of adverse

placement of sleep and work relative to circadian phase) inadequate to restore

performance and may be (in the case of optimal placement of sleep and work

relative to circadian phase) adequate or even unnecessary to sustain

performance. The FMCSA has commissioned scientific studies to evaluate the

efficacy of the current 34-hour restart rule and to provide information in support

of possible revisions to this rule.

Study Design

The objective of this project was to determine the effectiveness of the current

34-hour restart provision in the HOS regulations governing freight-carrying

CMV drivers with regard to restoring performance. Specifically, the

effectiveness of the 34-hour restart provision was evaluated using an inlaboratory experimental study design that tested cognitive task and driving

simulator performance.

A sample of 27 healthy subjects was studied in a “worst-case”–“best-case”

between-groups comparison of two 5-day (14-hour/day) work periods separated

by a 34-hour restart period. Half the sample was randomized to the “best-case”

condition, which entailed daytime wakefulness and work (and nighttime sleep)

throughout the study, including the 34-hour restart period. The other half was

randomized to the “worst-case” condition, which entailed nighttime wakefulness

and work (and daytime sleep) during the two 5-day work periods, while

transitioning back to a daytime schedule during the 34-hour restart period.

The main goal of the study was to evaluate whether the 34-hour restart period

was effective at maintaining performance in both conditions. To this end,

performance on a variety of cognitive tasks and on a high-fidelity driving

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.
simulator was measured throughout the study. The primary performance outcome measure was the

number of lapses (reaction times greater than 500 ms) on a 10-minute psychomotor vigilance test

(PVT), which is a validated tool for measuring the performance consequences of fatigue.

In the “best-case” condition, average PVT performance in the 5-day work period after the 34-hour

restart was the same as that in the 5-day work period before the 34-hour restart, indicating that the

restart period was effective at maintaining performance in this condition. In the “worst-case”

condition, however, average PVT performance in the 5-day work period after the 34-hour restart

was impaired relative to performance in the 5-day work period before the 34-hour restart,

indicating that the restart period was not effective at maintaining performance in the “worst-case”

condition (see Figure 1).

Similar effects were seen in other measures of performance, including driving performance on a

high-fidelity driving simulator. Subjects in the “worst-case” condition also displayed a progressive

increase in lane deviation over the hours of the night, which was accompanied by an increase of

up to 1 percent in fuel use. However, the objective observations of performance impairment during

the study were not reflected in subjective measures of sleepiness and mood, which inaccurately

suggested that some adaptation to the “worst-case” condition would occur.

Despite equal durations of sleep opportunity in the two study conditions, subjects in the “worstcase” condition did not manage to get enough sleep, due to the adverse circadian placement of the

sleep periods. All in all, the restart intervention, which involved transitioning back to a normal

nighttime sleep schedule during the 34-hour restart period, was not effective at mitigating the

sleep loss and consequent performance impairment in the “worst-case” condition.

The study findings highlight the importance of considering circadian effects on sleep and

performance in HOS regulations. The full, final report describes the methodology and the results

of the research study in detail.

Figure 1. Lapses on the 10-minute PVT as a function of days in the 5-day work

periods before and after the 34-hour restart period, for the “worst-case” (i.e.,

daytime sleep) and “best-case” (i.e., nighttime sleep) conditions (vertical error

bars indicate standard error).
Findings and Conclusions

The most important finding was that the effectiveness of the 34-hour restart provision in the present

HOS regulations depends on the circadian timing of sleep and wakefulness during the work

periods. The authors’ specific conclusions include:

u In the “best case” condition, average PVT performance in the 5-day work period after the

34-hour restart was the same as that in the 5-day work period before the 34-hour restart,

indicating that the restart period was effective at maintaining performance in this condition.

u In the “worst case” condition, average PVT performance in the 5-day work period after the

34-hour restart was impaired relative to average PVT performance in the 5-day work

period before the 34-hour restart, indicating that the restart period was not effective at

maintaining performance in this condition.

u Consistent with biological principles of sleep/wake regulation, PVT performance deficits in

the “worst case” condition were most prominent in the later hours of the night.

u Total sleep time was consistently reduced in the “worst case” condition relative to the “best

case” condition during the two 5-day work periods.

u Perhaps due to the temporary transitioning back to a normal nighttime sleep schedule

during the 34-hour restart period, the restart intervention did not effectively mitigate the

sleep loss and consequent performance impairment in the “worst case” condition (and

might even have contributed to the increased impairment after the restart).

u The level of PVT performance impairment reached in the “worst case” condition was

modest when compared to the documented effects of one night of acute total sleep

deprivation or a week of sustained sleep restriction to 6 hours per day.

u The research subjects were healthy young adults with no sleep disorders; results may be

different in a sample of patients with sleep apnea (widely reported to be common among

CMV drivers) or other medical conditions.

u Subjects in the “worst case” condition were subjectively sleepier than subjects in the “best

case” condition, but did not show an increase in sleepiness after the 34-hour restart period. Thus, subjective sleepiness did not accurately track objective performance impairment, and

can therefore not be relied upon to gauge level of impairment.

u Subjects in the “worst case” condition displayed an increase in lane deviation over the

hours of the night. This was accompanied by an increase of up to 1 percent in fuel use

across the night.

u Indices of driving impairment—speed variability, lane deviation, emergency braking

reaction time, and fuel use—were significantly predicted by lapses on the PVT

administered before driving.

Recommendations

The authors made a number of recommendations based on their conclusions from this study:

u Validation of fatigue and performance models for accurately predicting real-world driving

performance would allow for the development of model-based fatigue risk management

approaches, which could be mandated as a safe alternative for prescriptive HOS

regulations.

u Driver fatigue could be reduced by establishing work schedules and adapting HOS

regulations that allow greater flexibility (e.g., taking into account strategic napping and

circadian timing).

u Individuals cannot be relied upon to self-evaluate fatigue-induced impairment. This puts a

premium on development of individualized drowsy driver detection technologies and

fatigue education programs.
December 2010

Publication No. FMCSA-RRR-10-006

u Validation of the study findings in a sample of drivers in a real- world field study is important.

u Demonstration of the validity of fuel use on the driving simulators as

an index of fuel use in real trucks on real roads would provide

carriers with a bottom-line incentive to actively manage fatigue in

CMV drivers.

The full final report may be found online:

www.fmcsa.dot.gov/facts-research/art-public-reports.aspx.

Full report title:

Investigation Into Motor Carrier

Practices To Achieve Optimal

Commercial Motor Vehicle Driver

Performance: Phase I (Report No.

FMCSA-RRA-10-005)

Authored by:

Hans P.A. Van Dongen, PhD,

Gregory Belenky, MD

Performing Organization:

Sleep and Performance

Research Center

Washington State University

Spokane, WA

Key Words:

34-hour restart provision, circadian

rhythm, commercial motor vehicle,

fatigue, Hours-of-Service

regulations, performance, sleep,

worker recycling

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.

Web Site:

All FMCSA Tech and Analysis

Briefs may be accessed at

www.fmcsa.dot.gov.