FEDERAL HIGHWAY ADMINISTRATION • OFFICE OF MOTOR CARRIERS

FHWA Contact: Albert Alvarez, HCS-20, (202) 366-4706

Role of Driver Hearing in Commercial

Motor Vehicle Operation: An

Evaluation of the FHWA Hearing

Requirement

Introduction

The Federal Highway Administration (FHWA) currently requires that all commercial

motor vehicle (CMV) drivers have a specified minimum level of hearing to drive in 

interstate commerce. This tech brief summarizes an FHWA study of the same title that

evaluates the validity of the current CMV driver hearing requirements and the ability 

to hear as a critical requirement for safe driving.

Purpose

This study sought to answer many of the questions concerning truck driver hearing,

noise exposure, and hearing-critical tasks. A hearing requirement for CMV drivers

implies that commercial truck driving is a hearing-critical job, for reasons such as: crash

avoidance (car horns, train whistles), detection of in-cab auditory warning signals, and

face-to-face and CB communication.

There is a need to establish a more scientific and empirical basis for Federal CMV driver

hearing requirements. Some form of hearing requirement would be necessary if

research found driving tasks that are safety-critical and dependent on hearing.

Researchers had three main goals:

• to determine whether the current FHWA hearing requirement for CMV drivers is 

justified,

• to ascertain the level of hearing necessary to operate a commercial vehicle safely; and

• to determine whether such hearing requirements will be necessary in the future.

In completing the study, researchers also evaluated truck-cab noise as a cause for 

driver hearing loss, both temporary and permanent. 

Methodology

This research project consisted of four phases: a literature review; an extensive task

analysis; empirical measurement of driver hearing, truck-cab noise, and noise exposure;

and audibility predictions.

The literature review concentrated on the topics of commercial truck driving and 

hearing, the effects of occupational noise exposure, and truck-cab noise. An extensive

segment of the literature review focused on the effectiveness of the forced-whisper

test, one of the current screening methods for testing CMV driver hearing under 

Tech Brief

The vision of the Office of

Motor Carriers is to help

move people, goods, and

commercial motor vehicles

on our Nation’s highways in

the most efficient, economical, and crash-free manner

possible. The OMC research

and technology program

focuses on improving safety

in interstate commercial

motor vehicle operations and

serves a trucking and motor

coach industry that carries

more than 40 percent of all

intercity freight.

Studies are conducted in the

following areas: commercial

driver human factors, health,

and performance needs; new

and emerging driver and

vehicle technologies; safetyrelated data collection and

analysis needs; and performance-based changes to the

Federal Motor Carrier Safety

Regulations.

The OMC’s technology

research promotes safety by

identifying, collecting, and

communicating information

about technological

advances.

Office of Motor Carrier Research

and Standards

400 Seventh Street, SW

HCS-30; Room 3107

Washington, DC 20590
FHWA requirements. The next phase of the study was

a task analysis. Researchers first reviewed truck 

driving task analysis literature, much of which did not

consider the role of hearing or noise in the driving

task. Then they conducted structured interviews with

11 subject matter experts (SMEs). The input from the

SMEs was used to create an extensive task analysis

questionnaire that was distributed to 80 CMV drivers.

The measurement phase of this project sought to

determine the noise level in truck cabs, including

engine idle noise and noise in the sleeper berth.

Researchers took spectral measurements in several

trucks under different highway-speed driving 

conditions during actual commercial runs. They 

also used dosimetry to determine the noise doses

experienced by truck drivers during normal commercial runs of 8–18 hours; noise doses were measured 

in 9 sleeper berths. During this phase, researchers 

performed pre-and post-day audiograms for a group

of 10 drivers to determine whether truck drivers

experience temporary hearing loss after a normal 

driving shift.

The fourth and final study phase used the empirical

data collected in phase three to predict the audibility

of both speech and auditory signals that would be

encountered during normal truck driving. Speech

audibility was calculated for 16 listening conditions

(such as radios on, windows open, engine idle, etc.)

for both live and CB speech. Several warning signals

were also evaluated for audibility, including a backup

alarm, a siren, a train horn, and eight interior 

warning signals.

Findings

Literature Review

Researchers reviewed a wide range of literature; their

findings included:

• Persons who operate private vehicles with hearing

impairment may have better or worse safety

records than the non-hearing impaired, depending

on the study referenced.

• Based on the results of several studies, there

appears to be a relationship between noise, 

hearing level, and industrial accident rates. High

noise levels may lead to higher accident rates.

• Noise levels in truck cabs as reported over the last

25 years have dramatically decreased.

• There is evidence that noise can affect driver 

physiological functions, psychological functions, 

illness rates, and job performance.

Based on this extensive review of literature,

researchers also concluded that the forced-whisper

test is not as reliable or valid as a hearing test based

on pure-tone audiometry. 

A truly unbiased, comprehensive study of the validity

and reliability of the forced-whisper test has not been

attempted for over 50 years, during which the field of

audiology has made great strides. Audiometers have

become more widely available, and there are many

people trained in their use. While the forced-whisper

test is still a viable tool, pure-tone audiometry tests

are a more precise and objective way to evaluate

hearing. 

Task Analysis Results

The task analysis questionnaire was completed by 

80 CMV drivers. Questionnaire data produced a list 

of mechanical problems that can be detected by 

hearing. These data also provided researchers with a

tool to compile a final list of hearing-critical, routine

truck driving tasks, including: 

125 250 500 1K 2K 3K 4K 6K 8K

0

5

10

15

20

25

30

Frequency (Hz)

Mean Hearing Level (dBHL)

pre

post

Figure 1.

Mean pre- and post-workday audiograms 

for 10 drivers, left ear.

125 250 500 1K 2K 3K 4K 6K 8K

0

5

10

15

20

25

30

Frequency (Hz)

Mean Hearing Level (dBHL)

pre

post

Figure 2.

Mean pre- and post-workday audiograms 

for 10 drivers, right ear.
• Maneuvering in highway, city, and rural traffic

• Entering and exiting limited access highways

• Passing another vehicle

• Upshifting, downshifting, braking, accelerating, 

and parking

• Merging into traffic

• Emergency stopping

Based on the number of commercial driving tasks

identified as hearing-critical, and on the number of

hearing-critical incidents reported by CMV drivers

completing the questionnaire, this research suggests

that commercial truck driving should be classified as a

hearing-critical job.

Empirical Measurements

When measuring truck-cab noise, researchers found

that the overall broadband sound pressure level for

the 9 trucks evaluated was 89.1 dBA for 8 conditions

of highway driving. The sleeper-berth mean dBA was

81.6 dBA, and for engine idle conditions, cab noise

was 68.7 dBA. The truck-cab average of 89.1 dBA was

very close to the Occupational Safety and Health

Administration (OSHA) permissible exposure limit of

90 dBA for an 8-hour day. Interior noise levels in 

commercial motor vehicles are not regulated by

OSHA, but these regulations provide the best 

available metric for evaluating the risk of hearing loss

due to noise exposure.

Dosimetry was used to determine the noise doses

experienced by 10 truck drivers during normal 

commercial runs of 8-18 hours. Sleeper-berth doses

were much lower than front seat doses. The 8-hour

and projected 10-hour noise doses experienced by the

drivers in the study were not excessive as measured

against OSHA requirements for the general industry. 

However, the exposure levels were different for team

drivers who might be exposed to noise continuously,

as they rest and their partners drive. Team drivers

who spend most of their non-driving time in the cab

rather than the sleeper berth might be exposed to

noise levels that exceed recommended levels. The

noise doses were measured with rest breaks, meal

breaks, and refueling breaks included, so they 

represented realistic projections of actual truck trip

noise doses.

When pre-and post-workday audiograms were 

performed for a group of 10 drivers, results indicated

no temporary hearing loss, or temporary threshold

shift, after a normal driving shift. The pre- and 

post-workday audiograms were very similar, as shown

in figures 1 and 2. 

Researchers did measure a noise-induced permanent

threshold shift (NIPTS) when pre-work audiograms 

for a group of 30 CMV drivers were compared to

threshold data for non-noise exposed males of the

same mean age. The comparison showed significantly

higher thresholds at 3000, 4000, and 6000 Hz for the

drivers. But due to the prevalence of noisy hobbies

and previous occupations among the two groups, no

conclusions were reached as to whether the NIPTS

was caused by truck-cab noise.

Audibility Predictions

The results of the audibility predictions showed that

an acceptable level of intelligibility can be achieved

some of the time, but that speech communication,

both live and by CB radio, is degraded under noisier

truck-cab conditions. Intelligibility scores for the 

noisier conditions are unacceptably low, and vocal

efforts for live speech would need to be at an 

unsustainable level for reliable communication.

When researchers evaluated internal and external

warning signals for audibility, they found that the

probability of truck drivers hearing signals such as

train horns and sirens was very low. Signals were

found to exceed masked threshold of truck noise less

than half the time, and were almost never audible

under noisier conditions, meaning that CMV drivers

may be hearing less than 50 percent of external 

warning signals.

Recommendations 

Truck Manufacturers

This research found truck-cab noise to be unacceptably high for three reasons:

Table 1. 

Minimum Hearing Level Recommendations*

Audiometric Frequency Minimum Hearing Level

Recommendations

(Better Ear)

500 Hz 45 dBHL

1,000 Hz 45 dBHL

2,000 Hz 40 dBHL

3,000 Hz 40 dBHL

4,000 Hz 40 dBHL

*Current FHWA standards require an average hearing level of 40

dBHL at 500 Hz, 1,000 Hz, and 2,000 Hz. dBHL = decibel hearing

threshold level.
Researcher

This study was performed by

John G. Casali, Ph.D., Gary S.

Robinson, Ph.D., and Suzanne

E. Lee at Virginia Polytechnic

Institute and State University,

Department of Industrial and

Systems Engineering,

Telephone: (540) 231-9081.

Contract No.: DTFH61-95-C00172.

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 publication is now 

available. Copies can be

obtained from the National

Technical Information Service,

Telephone: (703) 605-6000.

Order No: PB98-114606.

Key Words

hearing, hearing standard,

noise exposure, hearing-critical

task, truck-cab noise, audibility

predictions, forced-whisper

test, task analysis, hearing loss.

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.

• The overall mean broadband sound pressure level for truck-cab noise is very near the

OSHA permissible exposure limit of 90 dBA for 8 hours.

• Truck-cab noise degrades communication in the truck to unacceptable levels under

many conditions.

• Noise levels often mask both interior and exterior warning signals, thus impacting

public safety.

For these reasons, researchers recommend that truck manufacturers make every effort

to decrease truck-cab noise in future models. Since this is a public health concern, noise

reducing features should become standard features in truck design. This research also

encourages manufacturers to ensure that in making the cab quieter, they do not

reduce the driver’s ability to hear external warning signals. Every effort should be

made to reduce the transmission of noise at the source: the engine.

Truck manufacturers could also ensure that truck-cab warning and advisory signals 

contain their primary energy in the frequency range from 700 to 3000 Hz, so that 

individuals suffering from a noise-induced hearing loss are still able to hear the signals.

To make in-cab auditory displays more audible, manufacturers can reduce the noise

level in the cab, or increase the presentation level of the signals.

Hearing Evaluations

Lacking empirical evidence that the forced-whisper test correlates with appropriate

hearing level requirements, the preferred choice for evaluating CMV driver hearing is

pure-tone audiometry, which can objectively assess hearing ability. Questionnaire 

results suggest that as many as half of all CMV drivers are already receiving this type of

hearing test. This research suggests that pure-tone audiometry tests are more objective

than the forced-whisper test, and could be substituted, with levels set according to

empirical measurements of signals needed to perform the truck-driving task safely.

Because hearing loss may exist at different frequencies, the FHWA currently evaluates

hearing at several levels (500 –2000 Hz). This study suggests that there may be some

benefit from testing CMV driver hearing at frequencies up to 4000 Hz. The pure-tone

audiometric test can more accurately assess hearing ability at specified frequency levels.

The overall conclusion of this report is that an FHWA hearing requirement is necessary.

There are both intentional signals and incidental sounds that CMV drivers need to hear

in order to drive safely. Table 1 presents the minimum recommended hearing levels for

the frequencies between 500 and 4000 Hz. These are based on a hearing level at 13

decibels below the masked threshold of the quietest truck-cab noise condition. 

Further Research

Further research in this area should concentrate on the development of an audiometric

database for truck drivers. A high proportion (84 percent) of the drivers surveyed in 

this study reported having hobbies or previous occupations with high levels of noise

exposure. Therefore, it is difficult to be certain that these drivers are suffering hearing

loss as a result of their driving activities. In conjunction with this database study, the

researchers recommended that a study of truck-cab noise be conducted every 2 or 3

years to determine whether truck-cab noise is increasing or decreasing.

Another research project might involve an analysis of the forced-whisper test to 

determine the variability and reliability of this test when used with various examiners

and patients. Research may also attempt to explore a correlation between pure-tone

audiometric tests and forced-whisper tests.

November 1998

Publication No. FHWA-MCRT-99-001