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INDIVIDUAL DIFFERENCES AND THE
"HIGH-RISK" COMMERCIAL DRIVER
SUMMARY This synthesis focuses on the "high-risk" commercial driver. Most truck and bus
drivers are both conscientious and safe, but the findings of this research project support
the notion, and widespread industry belief, that a relatively small percentage of commer-
cial drivers are associated with a significant and inordinate percentage of the overall
motor carrier crash risk.
This research project has attempted to document this phenomenon, explore related
factors, and identify ways that the high-risk driver can be targeted by various safety
management practices and other safety interventions. Expert industry opinion has
been accessed through survey questionnaires on the topic. The research literature on
the topic has been reviewed, with emphasis on the personal factors associated with
risk and carrier management approaches to reducing the problem. This synthesis
focuses on commercial (i.e., large truck and bus) drivers, but also presents the results
from a literature review on transportation operators in other modes such as air, rail,
and maritime.
Commercial motor vehicle (CMV) fleet safety managers are the principal audience
for this synthesis, although this synthesis is a presentation of findings, not a "how to"
guide to practice. In addition, the synthesis should be useful to government, industry,
and academic personnel involved in formulating and conducting studies to gain knowl-
edge (i.e., research) and to create tools (development) relating to this safety topic.
As noted, one basis for the research project was survey data collected from fleet safety
managers and "other experts" in motor carrier safety. Safety manager surveys were dis-
tributed primarily through a random sample mailing to carriers listed in the American
Trucking Associations fleet directory. In addition, survey forms were sent to people who
responded to a CTBSSP Synthesis 1 survey (also on carrier safety management), and, in
order to obtain motor coach segment respondents, some survey forms were distributed
to members of the American Bus Association Safety Council. The safety manager sur-
vey return rate was about 15%, so the sample cannot be described as representing the
CMV industry in general. Instead, it represents 178 interested managers from a variety
of CMV operations.
A second survey sample consisted of 67 other experts. These are individuals pro-
fessionally involved in CMV safety who are not fleet safety managers. This group
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includes former drivers and fleet managers, government regulatory and enforcement
personnel, industry trade association representatives, and researchers. Of course, these
are overlapping categories, and most other experts indicated several different motor
carrier safety-related professional experience areas.
The safety manager and other expert survey forms were parallel in their questions
and content, but there was one key difference. Regarding management practices, safety
managers were asked if they currently used the method and then, if "yes," they were
asked to rate its effectiveness. This yielded data on the percentage of carriers actually
using various methods and opinions of effectiveness of respondents actually using the
methods. For the other experts, parallel items only elicited evaluation ratings because
there were no questions regarding use.
Perhaps the most fundamental question about high-risk commercial drivers is whether
the problem is genuine and significant or the result of chance or other factors uncontrol-
lable by commercial drivers and their fleets. Survey findings strongly support the notion
that the problem is real and significant and that individual differences in safety among
drivers are enduring. Empirical data cited from a number of studies corroborate this
view, but do not sufficiently describe or explain the problem. In one cited study, for
example, large individual differences were seen in the rate of driver involvement in traf-
fic "near-miss" incidents, and 12% of the drivers in the study were associated with 38%
of the incidents. However, the study did not track drivers for a long period of time to
determine the degree of consistency of differential risk or the personal traits that could
produce enduring individual differences in risk.
Many factors affect commercial driver crash involvement. The focus of this syn-
thesis is on enduring personal risk factors. Nevertheless, at any given time, com-
mercial driver crash risk is affected by personal risk factors (e.g., hours of sleep the
previous night), vehicle risk factors (e.g., brake adjustment), environmental factors
(e.g., weather and roadway features), and, perhaps most important, risks created by
other drivers and traffic. "Accident proneness" was originally conceptualized nearly
100 years ago. Early concepts of it considered it an innate, unitary trait, a view that
is no longer widely held. However, it certainly appears that individual differences in per-
sonality and performance predispose some people to increased crash risk. Driver errors
can be violations of rules, mistakes of judgment, inattention errors, or inexperience
errors. Common driver errors resulting in crashes include recognition errors (failure
to perceive a crash threat) and decision errors (risky driving behavior such as tail-
gating), or poor decision-making in dynamic traffic situations (such as trying to cross
a stream of traffic).
There are many personal dimensions that may be correlated with individual crash
risk. In the research project survey, respondents were asked to rate the strength of asso-
ciation of 16 such factors with crash risk. Personality traits such as aggressiveness,
impulsivity, and inattentiveness were rated by both respondent groups as having the
highest associations with risk.
This synthesis reviews literature relating to the following factors related to com-
mercial driver risk. A number of factors potentially correlate with risk and may
be the basis for safety interventions to reduce risk. Factors discussed include the
following:
· Driver age and gender
· Driving history
Commercial driving experience
Longevity with company
Crashes, violations, and incidents
Defensive driving
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· Non-driving criminal history
· Medical conditions and health
Sleep apnea
Narcolepsy
Diabetes
Other medical conditions
· Alcohol and drug abuse
· Driver fatigue
· Personality
Impulsivity and risk-taking
Social maladjustment and aggressive/angry personalities
Introversion-extroversion
Locus of control
Extreme ("dichotomous") thinking
· Sensory-motor performance
· Other risk factors
Stress
Recent involvement in other crashes
Safety belt use
· Risks identified in other transportation modes
Maritime operations
Rail
Aviation
Fleet safety management approaches to preventing high-risk-driverrelated
crashes revolve around the basic management functions of selection and hiring, per-
formance evaluation, and driver safety management practices. The clearest advice to
safety managers is, "Don't hire a problem." Methods for improving driver selection and
job aids for safety managers are provided in Appendix F.
Once drivers are hired, there are various ways to monitor their driving behaviors and
modify their behavior in ways that reduce risk. Performance evaluation and feedback
(perhaps enhanced by on-board safety monitoring of driver behavior), training and coun-
seling, performance incentives, behavior-based safety, and driver self-management are
among the methods described. Of course, termination may be the ultimate solution when
drivers are unmanageable from the safety perspective.
Recommended research and development (R&D) to address the problem of high-risk
drivers includes the following:
· Verification of the reliability of research findings indicating differential driver
risk.
· Determination of how enduring these differences are across time. To the extent that
they are enduring, they constitute personal traits. To the extent that they change,
they likely reflect short-term personal conditions (states) or purely situational
factors.
· The conducting of case control or other driver studies that profile individual driver
differences within a group of drivers and relate these differences to safety outcomes
(e.g., crashes).
· Creation and field testing of various types of driver selection instruments.
· Investigation of individual fatigue susceptibility. Research should verify that dif-
ferences in fatigue susceptibility are long-term personal traits and identify ways to
assess the level of fatigue susceptibility. Highly susceptible individuals should not
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be hired as commercial drivers or should receive special attention, including med-
ical screening for sleep disorders and counseling about sleep hygiene habits.
· Documentation of the best driver management practices for use by carrier safety
managers and dissemination of this information throughout the industry.
· Industry pilot testing of behavioral safety management techniques, perhaps en-
hanced by the use of on-board safety monitoring of driver safety performance
and behaviors. This should include determination of the effectiveness of various
management interventions including both positive rewards and negative discipline
(punishment).
