FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION

FMCSA Contact: Albert Alvarez, MC-RTR, (202) 358-5684

A Study of Prevalence of Sleep

Apnea Among Commercial Truck

Drivers

Introduction

Staying awake means staying alive. This is a slogan used to describe a research study on

sleep apnea sponsored by the Federal Motor Carrier Safety Administration (FMCSA) and

the American Transportation Research Institute of the American Trucking Associations

(ATA). The research project addressed the prevalence of sleep apnea among commercial

truck drivers, potential risk factors, and its impact on driving performance.

This Tech Brief summarizes the project's final report, A Study of Prevalence of Sleep Apnea

Among Commercial Truck Drivers.

Background

Sleep apnea is a major contributor to daytime drowsiness—a condition that could prove

deadly for commercial truck drivers and involved passenger vehicles. It is a condition

where, during sleep, a narrowing or closure of the upper airway causes repeated sleep

disturbances leading to poor sleep quality and excessive daytime sleepiness. Since

excessive sleepiness can be a consequence of sleeping disturbances, drivers with sleep

apnea have compromised driving performance leading to increases in the risks of crashes.

According to the Divided Attention Driving Task, a research test designed to mimic driving

performance, individuals with sleep apnea perform, on average, as poorly as individuals

whose levels of blood alcohol concentration exceed the legal limit. The results of this

study show that the prevalence rates of sleep apnea among commercial truck drivers are

similar to sleep apnea rates found in other general populations. This is in contrast to the

extremely high prevalence rates reported previously by the Stoohs study. [Stoohs, Sleep

and Sleep-Disordered Breathing in Commercial Long-Haul Truck Drivers, 1995]

Purpose

This research study had three objectives:

• To estimate the prevalence of sleep apnea among a sample of commercial truck drivers

living within a 50-mile radius of the University of Pennsylvania

• To examine the relationship in commercial truck drivers between severity of sleep apnea

and decreased function related to driving performance

• To develop a profile of an overall sample of commercial truck drivers with regard to

their sleep apnea-related characteristics and risks

Methodology

To estimate prevalence of sleep apnea in a sample population, researchers had to decide

the following: sample population to be studied, higher risk and lower risk categories for

likelihood of sleep apnea, placement category for in-laboratory testing, and methods to be

used for in-laboratory testing.

The goal of the Federal Motor

Carrier Safety Administration

(FMCSA) is to reduce commercial

vehicle related fatalities, as well as

the number of persons injured in

commercial vehicle related crashes,

by 50 percent by the year 2010. 

FMCSA's Research and Technology

programs encompass a range of

issues and disciplines, all related to

motor carrier and bus safety and

security. FMCSA defines a

"research program" as any

systematic study directed toward

fuller scientific discovery,

knowledge, or understanding that

will improve safety and security,

and reduce the number and

severity of commercial motor

vehicle crashes. Similarly, a

"technology program" includes

those that adopt, develop, test

and/or deploy innovative driver

and/or vehicle best practices, and

technologies that will improve

safety and security, and reduce the

number and severity of commercial

motor vehicle crashes. 

Currently, FMCSA's Office of

Research and Technology conducts

programs in the area of Driver

Safety Performance, Commercial

Vehicle Safety Performance, Carrier

Compliance and Safety, Safety

Systems and Technology, CrossCutting Safety Initiatives, and

Security. The study described in

the following Tech Brief was

designed and developed as part of

FMCSA's Research and Technology

Driver Safety Performance

Program. The primary goals of this

program are to improve the safety

behavior of non-commercial

drivers in the vicinity of trucks and

buses, and ensure that commercial

drivers are physically qualified,

trained to perform safely, and

mentally alert. 

Office of Research and Technology

400 Virginia Ave, SW

Suite 600

Washington, DC 20024

Tech Brief
Sample Population

The first step in estimating the prevalence of sleep apnea was to decide on a target population or population of

interest for the study. Two approaches were considered when evaluating commercial truck drivers, before

selecting the most applicable method. The first approach based the sample on drivers of specific commercial

driving companies. However, there was concern that the hiring practices of some commercial driving companies

may have specific features affecting the nature of their driver population, thereby improperly influencing the

sampling pool. The second approach, and the one upon which this study was based, used a target population

based on a random sample of commercial driver's license (CDL) holders living within 50 miles of the University of

Pennsylvania. This approach had the advantage of a precisely defined sampling frame, which permitted a true

random sample of 4,826 commercial truck drivers in a precisely defined population. The Pennsylvania

Department of Motor Vehicles provided the random sample of CDL holders. Approximately 31.5 percent, or 1,391

participants, responded. 

Higher Risk, Lower Risk and Placement Categories for Likelihood of Sleep Apnea

To determine the placement into higher risk and lower risk categories for the likelihood of sleep apnea, an

instrument called a Multivariable Apnea Prediction (MAP) was used to calculate a MAP score based on age,

gender, and body mass index (which measures the degree of obesity). Responses to survey questions about

symptoms of sleep apnea also were evaluated as part of the calculation of each driver's MAP score. Of the total

scores, 778 drivers scored high on the MAP and were placed in the higher risk group, while 551 drivers with low

MAP scores made up the lower risk group. All drivers who were placed in the higher risk category were enrolled

in in-laboratory testing, while those placed in the lower risk category were enrolled in random order for 

in-laboratory testing. 

Methods for In-Laboratory Testing

All in-laboratory participants were assessed using multiple instruments with regard to their subjective perception

of sleepiness and functional impairment, as well as objective measures of sleepiness, lack of attention, and other

functional consequences of sleepiness. Various methods of testing were used in analyzing both subjective and

objective measures of sleepiness. Methods to analyze subjective measures included self-report questionnaires,

which measured drivers' self-perception of sleepiness and functional impairment. Methods to analyze objective

measures included assessment of reaction times, performance lapses, and lane tracking ability.

Subjective Measures of Sleepiness: 

• Epworth Sleepiness Scale

Drivers were asked to complete a simple self-administered questionnaire of eight items measuring their

general level of daytime sleepiness, whereby they rated the likelihood of dozing off or falling asleep

when in various situations commonly encountered in daily life, such as watching television, or being a

passenger in a car.

• Karolinska Sleepiness Scale

This highly sensitive measurement scale for sleepiness was conducted on drivers who experienced

shortened sleep duration the previous night. Participants, who were sleepy during the test, encountered

intrusions of sleep episodes into their normal states of wakefulness. This test measures "sleep intrusions"

into states of wakefulness.

• Stanford Sleepiness Scale (SSS)

This test is a single seven-item subjective measure scale for sleepiness. It asks the participants to circle the

statement that best describes how sleepy they feel at the moment they are answering the question. 

• Functional Outcomes of Sleep Questionnaire (FOSQ)

This is a self-report measure designed to assess the impact of disorders of excessive sleepiness on multiple

activities of everyday living. This test is used to determine how disorders of excessive sleepiness affect

participants' ability to conduct normal activities and the extent to which these abilities are improved by

effective treatment of excessive daytime sleepiness.
Objective Measures of Sleepiness:

• Multiple Sleep Latency Test

This test, which measures the psychological pressure to fall asleep, studied the rate at which drivers fell

asleep during daytime naps. Drivers were asked to fall asleep in a dark room at two-hour intervals,

where the length of time it took to fall asleep was measured and the average of all nap opportunities

was calculated.

• Psychomotor Vigilance Test (PVT)

Using a handheld device with a small visual display, this test measured driver reaction time to stimuli over

a 10-minute period. Measurements that are sensitive to the effects of sleep loss, such as median reaction

time, number of performance lapses, lapse duration, and optimum response time, were recorded.

• Divided Attention Driving Task

Designed to mimic driving performance, participants were tested using a driver-like model. They used a

steering wheel device to track randomly moving targets, while simultaneously responding to numbers

that randomly appeared at the corners of a computer screen. Each driver's average deviation from the

desired center point and slope of increase was computed over the time of the test. 

• Digit Symbol Substitution Test (DSST)

This test assessed cognitive speed and accuracy by subjecting drivers to a 90-second test, whereby the

participant viewed nine identified symbols and was asked to identify one symbol at a time by typing its

corresponding number. As soon as the driver responded, a new symbol appeared. Excessive sleepiness

greatly affected the ability to perform this test. 

Findings

A major goal of the study was to determine the prevalence of sleep apnea in commercial truck drivers, based on

the results of several tests conducted on a random sample of commercial driver's license (CDL) holders living

within a 50-mile radius of the University of Pennsylvania. The results of the study revealed that 17.6 percent of

CDL holders had mild sleep apnea, 5.8 percent had moderate sleep apnea, and 4.7 percent had severe 

sleep apnea. 

A significant research finding was that although sleep apnea is common among commercial vehicle drivers, its

prevalence is considerably less than the 78 percent reported for mild sleep apnea of CDL holders in the Stoohs

study. Instead, the rates of prevalence are more similar to study results in other, more general populations,

rather than commercial truck drivers as a group. 

The study also revealed that the prevalence of sleep apnea depends on the relationship between two major

factors, age and degree of obesity, with prevalence increasing with both. This relationship is important, because

it provides the commercial driving industry with predictions that are useful in estimating the prevalence of sleep

apnea in any population of drivers.

Another meaningful study finding showed that the prevalence of sleep apnea depends on the average duration

of sleep over consecutive nights at home. Short sleep duration, six hours or less per night, results in an increase

in the prevalence of sleep apnea. It was revealed that sleep duration is affected by the time at which drivers

awake in the morning, and since more than 35 percent of commercial truck drivers terminate their sleep before

6:00 am, they have significantly shorter sleep durations and higher chances of daytime sleepiness. All measures

of sleepiness showed that the effects of daytime performance depend, not only on the severity of sleep apnea,

but also on the average sleep duration of the driver. 

A large number of drivers indicated self-reported sleepiness on the subjective tests; however, it was not a

determining factor of the presence and severity of sleep apnea, since no relationship was found between selfreport measures and any of the performance ability tests. This lack of relationship is unclear, and indicates that

self-reports of sleepiness are not a reliable source in identifying drivers who are likely to have sleep apnea.

Conversely, almost all of the objective tests of performance showed a clear relationship between performance

ability and the severity of sleep apnea, i.e. the relationship between the measurement of sleepiness, and rate of

performance lapses and lane tracking ability. 
U.S. Department of Transportation

Researcher

This study was performed by the

Trucking Research Institute,

American Trucking Associations

Foundation, 2200 Mill Road,

Alexandria, VA 22314. Contract

No. DTFH61-93-R-00088.

Distribution

This Tech Brief is being

distributed according to a

standard distribution. Direct

distribution is being made to the

Service Centers and Divisions.

Availability

The study final report FMCSART-02-030 is available from the

National Technical Information

Service (PB2002-108226).

Key Words

Altertness Performance;

Commercial Drivers; Daytime

Sleepiness; Driving Tasks;

Performance Measures;

Prevalence of Sleep Apnea;

Sleep Apnea; Sleep Deprivation;

Sleep Duration.

Notice

This Tech Brief is disseminated

under the sponsorship of the

Department of Transportation in

the interest of information

exchange. The Tech Brief

provides a synopsis of the

study's final publication. The

Tech Brief does not establish

policies or regulations, nor does

it 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:

http://www.fmcsa.dot.gov.

Technical Writer

Craig Steinberg

C2 Technologies, Inc.

July 2002

Publication No. FMCSA-RT-02-080 

Since sleep apnea and shortened sleep duration were prevalent in the CDL test group, any

effort to deal with impaired driving performance, as a result of excessive sleepiness, needs

to consider both issues. These issues are important, since the risk of having sleep apnea is

higher in CDL holders who have shorter durations of sleep. Although the prevalence of

severe sleep apnea and chronic inadequate sleep among commercial truck drivers gives rise

to serious concerns, it can be a reversible condition with effective treatment. However, a

major challenge to ensuring driver safety against the adverse effects of sleep apnea is to

develop cost-effective ways of identifying at-risk drivers, and ensuring a solution to this

treatable and preventable problem. 

Recommendations

Based on the results of the sleep apnea research project, researchers offered several

recommendations to address the problems with the prevalence of sleep apnea among

commercial truck drivers. These suggestions, however, do not necessarily represent the

position or policies of the FMCSA. The recommendations include the following:

• Conduct research to assess the role of sleep apnea in crash causation for commercial

vehicles

• Conduct research as to the efficacy of different strategies in order to identify

commercial truck drivers with severe sleep apnea or chronic sleep deprivation

• Convene a committee of experts from various backgrounds to review and develop

public policies on sleep apnea and make appropriate recommendations

References

Pack, Allen I.; Dinges, David F.; Maislin, Greg. A Study of Prevalence of Sleep Apnea Among

Commercial Truck Drivers, FMCSA, Publication No. DOT-RT-02-030, Washington, DC, 20002

Federal Motor Carrier Safety Administration