Researcher

This study was performed by

the Trucking Research Institute,

Alexandria, VA, Applied Science

Group, Inc., Bedford, MA, the

Institute of Circadian

Physiology, White Plains, NY,

and the Liberty Mutual

Research Center, Hopkinton,

MA, in collaboration with

Professor John Stern of

Washington University, St.

Louis, MO. Contract No.

DTFH61-96-00022.

Distribution

This Tech Brief is being distributed according to a standard

distribution. Direct distribution

is being made to the Resource

Centers and Divisions.

Availability

The study final report will be

available from the National

Technical Information Service,

Telephone: (703) 605-6000.

Key Words

eye tracking, ocular dynamics,

fatigue, alertness, simulator,

napping.

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 FHWA endorsement of

the conclusions or recommendations. The U.S. Government

assumes no liability for its 

contents or their use.

found it difficult to complete the four scheduled night driving sessions after spending

only 5 hours in bed. Several drivers were unable to start or finish the third scheduled

driving run and were permitted to take an unscheduled nap instead, both in the Nap

and No-Nap conditions.

Interestingly, the unscheduled naps, which lasted for 1 to 2 hours, had few beneficial

effects. For example, subjective sleepiness and fatigue levels remained almost as high

as they were at the end of the second night driving run. More importantly, driving 

performance was worse during the fourth driving run, after the unscheduled nap, 

than it was during the second, as indicated by larger penalties and more crashes. 

These results suggest that preventative naps may be more beneficial than recuperative

naps during all-night driving situations. Other studies have shown that naps taken 

early within a long period of sustained wakefulness have more beneficial effects than

naps taken at later times. Researchers suggested that this be tested experimentally in

future studies of scheduled napping as a fatigue countermeasure in long-haul driving

operations.

April 1999

Publication No. FHWA-MCRT-99-010
including two 2-hour practice driving runs on the 

driving simulator.

The participants then slept in the laboratory, but time

in bed was restricted to 5 hours. The second day

included a 2-hour baseline driving run starting at

10:00 a.m. At the end of the driving run, the drivers

completed the following tests: two Visual Analog

Scales (VAS) for assessing subjective sleepiness and

fatigue; resting electroencephalogram (EEG) recordings; and three computerized performance tests. 

The performance tests included a visual search and

recognition task; a time estimation task; and a visualmotor coordination task.

Drivers in the Nap condition took a 3-hour nap in 

the afternoon, while drivers in the No-Nap condition

spent that time engaged in various sedentary 

activities. The schedule then called for VAS, EEG, and

performance testing, before drivers began a series of

four 2-hour driving runs beginning at 10:00 p.m. Each

driving run was followed by additional testing.

Polysomnographic recordings were obtained during

all scheduled sleep episodes.

Truck Driving Simulator

A fixed-base simulator was used to replicate the

essentials of driving in a medium-sized heavy truck.

During each driving run, participants encountered a

sequence of interactive driving events, including

straight and curved road segments; signalized and

non-signalized intersections; workzones; oncoming

vehicles, some of which encroached in the drivers’

lane; and crosswinds. Drivers were also required to

detect “pedestrians” appearing along the roadway

and respond to specially designed target images 

presented in the rear view mirrors. 

A monetary reward/penalty system was used to

encourage participant motivation and good driving

performance. Drivers were rewarded for finishing a

run in less than a specified time, and were penalized

for incidents like collisions, off-road accidents, and

speeding tickets. Participants received a bonus for

good performance, but were not actually required to

pay a negative balance.

Eye Tracker

The eye tracker system used in this study acquired eye

measurement data on all test participants, including

blink duration and partial eye closures. The analyses

performed on the data collected by the eye tracker

sought to: 

• Identify a number of blink and eyelid closure 

parameters;

-60 -50 -40 -30 -20 -10 0 10 20 30

0.15

0.14

0.13

0.12

Time before/after off-road accident (sec)

Blink closing

duration (sec)

Figure 1.

Mean blink closing duration.

Mean blink closing duration for seven

participants. (Due to loss of data, results

for two drivers could not be evaluated.)

Closing duration began to decrease in

the 10-second time period immediately

preceding an accident and was the

shortest in the 30 seconds following 

the accident.

-60 -50 -40 -30 -20 -10 0 10 20 30

100

80

60

40

20

0

Time before/after off-road accident (sec)

Lid closures (%)

Figure 2.

Eyelid closure occurrences.

Eyelid closure occurrences of the same

seven participants per 10-second period,

converted to a percentage. (Eight 

accidents were selected per subject; the

maximum number of eyelid closures 

was 56.) It was readily apparent that the

10-second period immediately preceding

the accident had the largest number 

of lid closures. The frequency of lid 

closures began to increase 20–30 seconds before the accident and showed a

gradual decrease during the 30 second

period following the accident. The 

duration of eyelid closures lasted from

0.5 seconds to 22 seconds.
including two 2-hour practice driving runs on the 

driving simulator.

The participants then slept in the laboratory, but time

in bed was restricted to 5 hours. The second day

included a 2-hour baseline driving run starting at

10:00 a.m. At the end of the driving run, the drivers

completed the following tests: two Visual Analog

Scales (VAS) for assessing subjective sleepiness and

fatigue; resting electroencephalogram (EEG) recordings; and three computerized performance tests. 

The performance tests included a visual search and

recognition task; a time estimation task; and a visualmotor coordination task.

Drivers in the Nap condition took a 3-hour nap in 

the afternoon, while drivers in the No-Nap condition

spent that time engaged in various sedentary 

activities. The schedule then called for VAS, EEG, and

performance testing, before drivers began a series of

four 2-hour driving runs beginning at 10:00 p.m. Each

driving run was followed by additional testing.

Polysomnographic recordings were obtained during

all scheduled sleep episodes.

Truck Driving Simulator

A fixed-base simulator was used to replicate the

essentials of driving in a medium-sized heavy truck.

During each driving run, participants encountered a

sequence of interactive driving events, including

straight and curved road segments; signalized and

non-signalized intersections; workzones; oncoming

vehicles, some of which encroached in the drivers’

lane; and crosswinds. Drivers were also required to

detect “pedestrians” appearing along the roadway

and respond to specially designed target images 

presented in the rear view mirrors. 

A monetary reward/penalty system was used to

encourage participant motivation and good driving

performance. Drivers were rewarded for finishing a

run in less than a specified time, and were penalized

for incidents like collisions, off-road accidents, and

speeding tickets. Participants received a bonus for

good performance, but were not actually required to

pay a negative balance.

Eye Tracker

The eye tracker system used in this study acquired eye

measurement data on all test participants, including

blink duration and partial eye closures. The analyses

performed on the data collected by the eye tracker

sought to: 

• Identify a number of blink and eyelid closure 

parameters;

-60 -50 -40 -30 -20 -10 0 10 20 30

0.15

0.14

0.13

0.12

Time before/after off-road accident (sec)

Blink closing

duration (sec)

Figure 1.

Mean blink closing duration.

Mean blink closing duration for seven

participants. (Due to loss of data, results

for two drivers could not be evaluated.)

Closing duration began to decrease in

the 10-second time period immediately

preceding an accident and was the

shortest in the 30 seconds following 

the accident.

-60 -50 -40 -30 -20 -10 0 10 20 30

100

80

60

40

20

0

Time before/after off-road accident (sec)

Lid closures (%)

Figure 2.

Eyelid closure occurrences.

Eyelid closure occurrences of the same

seven participants per 10-second period,

converted to a percentage. (Eight 

accidents were selected per subject; the

maximum number of eyelid closures 

was 56.) It was readily apparent that the

10-second period immediately preceding

the accident had the largest number 

of lid closures. The frequency of lid 

closures began to increase 20–30 seconds before the accident and showed a

gradual decrease during the 30 second

period following the accident. The 

duration of eyelid closures lasted from

0.5 seconds to 22 seconds.
Researcher

This study was performed by

the Trucking Research Institute,

Alexandria, VA, Applied Science

Group, Inc., Bedford, MA, the

Institute of Circadian

Physiology, White Plains, NY,

and the Liberty Mutual

Research Center, Hopkinton,

MA, in collaboration with

Professor John Stern of

Washington University, St.

Louis, MO. Contract No.

DTFH61-96-00022.

Distribution

This Tech Brief is being distributed according to a standard

distribution. Direct distribution

is being made to the Resource

Centers and Divisions.

Availability

The study final report will be

available from the National

Technical Information Service,

Telephone: (703) 605-6000.

Key Words

eye tracking, ocular dynamics,

fatigue, alertness, simulator,

napping.

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 FHWA endorsement of

the conclusions or recommendations. The U.S. Government

assumes no liability for its 

contents or their use.

found it difficult to complete the four scheduled night driving sessions after spending

only 5 hours in bed. Several drivers were unable to start or finish the third scheduled

driving run and were permitted to take an unscheduled nap instead, both in the Nap

and No-Nap conditions.

Interestingly, the unscheduled naps, which lasted for 1 to 2 hours, had few beneficial

effects. For example, subjective sleepiness and fatigue levels remained almost as high

as they were at the end of the second night driving run. More importantly, driving 

performance was worse during the fourth driving run, after the unscheduled nap, 

than it was during the second, as indicated by larger penalties and more crashes. 

These results suggest that preventative naps may be more beneficial than recuperative

naps during all-night driving situations. Other studies have shown that naps taken 

early within a long period of sustained wakefulness have more beneficial effects than

naps taken at later times. Researchers suggested that this be tested experimentally in

future studies of scheduled napping as a fatigue countermeasure in long-haul driving

operations.

April 1999

Publication No. FHWA-MCRT-99-010