National Institute on Alcohol Abuse and Alcoholism No. 31 PH 362 January 1996
Drinking and Driving
Driving involves multiple tasks, the demands of which
can change continually. To drive safely, one must maintain alertness, make
decisions based on ever-changing information present in the environment, and
execute maneuvers based on these decisions. Drinking alcohol impairs a wide
range of skills necessary for carrying out these tasks. This Alcohol
Alert examines alcohol impairment of driving skills and describes some
factors that increase motor vehicle crash risk.
Some Factors That Influence Crash Risk
Blood alcohol concentration. The proportion of alcohol
to blood in the body is expressed as the blood alcohol concentration (BAC). In
the field of traffic safety, BAC is expressed as the percentage of alcohol in
deciliters of blood--for example, 0.10 percent (i.e., 0.10 grams per deciliter).
A 160-pound man will have a BAC of approximately 0.04 percent 1 hour after
consuming two 12-ounce beers or two other standard drinks on an empty stomach
(1).
All State laws stipulate driver BAC limits, which now vary by
State. According to these laws, operating a vehicle while having a BAC over the
given limit is illegal (2). The BAC limit for drivers age 21 and older in most
States is 0.10 percent, although some States have reduced the limit to 0.08
percent.
The many skills involved in driving are not all impaired at the
same BAC's (3). For example, a driver's ability to divide attention between two
or more sources of visual information can be impaired by BAC's of 0.02 percent
or lower (3-5). However, it is not until BAC's of 0.05 percent or more are
reached that impairment occurs consistently in eye movements, glare resistance,
visual perception, reaction time, certain types of steering tasks, information
processing, and other aspects of psychomotor performance (3,4,6,7).
Research has documented that the risk of a motor vehicle crash
increases as BAC increases (3,4,8) and that the more demanding the driving task,
the greater the impairment caused by low doses of alcohol (3). Compared with
drivers who have not consumed alcohol, the risk of a single-vehicle fatal crash
for drivers with BAC's between 0.02 and 0.04 percent is estimated to be 1.4
times higher; for those with BAC's between 0.05 and 0.09 percent, 11.1 times
higher; for drivers with BAC's between 0.10 and 0.14 percent, 48 times higher;
and for those with BAC's at or above 0.15 percent, the risk is estimated to be
380 times higher (8).
Youth. Youthful age has been cited as one of the most
important variables related to crash risk (9). Young drivers are inexperienced
not only in driving but in drinking and in combining the two activities (9). In
1994, almost 7,800 persons ages 16 through 20 were drivers in fatal motor
vehicle crashes (10). Twenty-three percent of these drivers, for whom drinking
any quantity of alcohol is illegal, had BAC's of 0.01 percent or higher,
compared with 26 percent of drivers age 21 and older (10).
According to Hingson and colleagues, each 0.02-percent increase
in BAC above 0.00 percent places 16- to 20-year-old drivers at greater risk for
a crash than older drivers (11). Roadside surveys indicate that young people are
less likely than adults to drive after drinking; however, especially at low and
moderate BAC's, their crash rates are substantially higher than those of other
groups (9).
Driving inexperience and immaturity are considered to be the
main causes of motor vehicle crashes among drivers ages 16 to 20, even when
alcohol is not involved (9). In one study, Hingson and colleagues concluded that
drivers in th is age group have a greater risk than older drivers of being
involved in a fatal crash even with a BAC of 0.00 percent (11). Young people's
lack of driving experience renders them less likely than more experienced
drivers to cope successfully with hazardous situations (9). This, combined with
a penchant for risk-taking driving behavior such as speeding--along with a
tendency both to underestimate the dangerous consequences of such behaviors and
to overestimate their driving skill--contributes to the high crash rate among
young drivers (12,13).
Gender. Twenty-nine percent of male drivers involved in
fatal motor vehicle crashes had BAC's of 0.01 percent or greater, compared with
15 percent of female drivers (10). However, studies indicate that at BAC's
ranging from 0.05 to 0.09 percent, crash risk may be greater for females than
for males (8,14). Research shows that women metabolize alcohol differently from
men, causing women to reach higher BAC's at the same doses (4,15). However,
laboratory studies of alcohol impairment of driving skills among women are rare
and the results are inconclusive (6).
Combining medications with alcohol and driving.
Combining certain medications with alcohol increases crash risk. Sedatives and
tranquilizers alone can impair driving skills (16) and can impair them even more
when combined with alcohol (17-20). For example, low doses of flurazepam, a
sedative-hypnotic prescribed for the treatment of insomnia, alone can impair a
driver's ability to steer. The effect of this medication can be compounded with
even a small dose of alcohol consumed the next morning (20). Driving skills can
be impaired by other medications, such as codeine, as prescribed to treat
moderately severe pain (20). When combined with alcohol, such medications'
adverse effects on driving skills are exacerbated, as are the effects of some
antidepressants, most antihistamines, certain cardiovascular medications, and
some antipsychotic medications (20).
Alcohol tolerance. The repeated performance of a
particular task in association with alcohol consumption can lead to the
development of a form of adaptation referred to as "learned" or "behavioral"
tolerance (21). Learned tolerance can reduce the
alcohol-induced impairment
that would ordinarily accompany the performance of that particular task (21).
However, when conditions change or when something unexpected occurs, the
tolerance acquired for that task can be negated (22).
These findings may be applicable to the performance of tasks
involved in drinking and driving (21,23). A driver who has developed behavioral
tolerance to driving a familiar car over a particular route under routine
circumstances may drive without being involved in a crash, despite consumption
of some alcohol (21,23). However, when encountering a novel environment--for
example, a detour--or an unexpected situation, such as a bicycle darting in
front of the car, this same driver would be at the same risk for a crash as a
novice driver at the same BAC, due to lack of prior learning opportunities for
these unexpected events.
Legal Sanctions for DUI Offenders
Legal sanctions, such as driver's license suspension and
court-ordered alcoholism treatment, are designed to deter drinking and driving
(24). Driver's license suspension and license revocation seem to be the most
effective deterrents among the general driving population (24). However, a
meta-analysis of deterrent strategies targeted to the drinking-and-driving
population concluded that the most effective means for reducing rearrest for
driving under the influence of alcohol (DUI) and crashes was a combination of
license suspension and interventions such as education, psychotherapy/
counseling, and some followup (25).
Researchers contend that court-ordered treatment should be
considered an adjunct, not an alternative, to license sanctions (24). According
to Sadler and colleagues, a DUI conviction should serve to identify problem
drinkers and guide or coerce them into alcohol treatment (26). Alcohol treatment
for DUI offenders can range from short-term educational sessions to therapy
programs lasting at least 1 year (24).
Treatment of convicted drinking drivers normally emphasizes
modifying drinking behavior (24). The type and duration of treatment depend on
factors such as the severity of the person's drinking problem and DUI history
(24,27). DUI offenders with less severe drinking problems benefit most from
educational programs (24,27), although no known model is thought to be most
effective (24) in reducing recidivism or alcohol-related crashes. For repeat
offenders or those with more seve re drinking problems, therapy that lasts for
at least 12 months (24) and that includes intensive programs focused on the
individual appears to be most effective (27).
Prevention
The National Highway Traffic Safety Administration (NHTSA)
credits State laws raising the legal drinking age to 21 with preventing almost
1,000 traffic deaths annually (11). Legislation to reduce the BAC limit to 0.02
percent or lower, referred to as the "zero tolerance law" for young drivers, has
been passed by 29 States and the District of Columbia to reduce alcohol-related
fatalities further (10,11). The National Highway Systems Act provides incentives
for all States to reduce their BAC limits for drivers under 21 to 0.02 percent
beginning October 1, 1998.
One study (11) examined the effectiveness of lowering BAC
limits for young people in States where such laws have been in force for at
least 1 year. The researchers found that after the BAC limits were lowered to
0.00 or 0.02 percent, the proportion of nighttime fatal crashes involving single
vehicles in this age group dropped 16 percent.
Drinking and Driving--A Commentary by
NIAAA Director Enoch Gordis, M.D.
Progress has been made in reducing the consequences of
drinking and driving; the percent of alcohol-related crash fatalities has
declined from 43.6 percent of the total number of traffic crash fatalities in
1986 to 37.4 percent in 1992. Advances in technology (i.e., automobile
engineering and road design), less public acceptance of drinking drivers,
decreases in per capita consumption, and a growing willingness by the States to
adopt public policies aimed at preventing alcohol-related injuries and deaths
and enforce legal sanctions against drinking drivers may all be factors in this
decline. Newer policies, such as the mandated "zero tolerance" for underage
youth, have been shown to reduce crashes in this vulnerable age group.
Additionally, increased attention to prevention programs that both impact on and
affect adult behavior, such as server training, the designated driver concept,
and intervention and education programs in secondary schools and colleges, have
demonstrated some effectiveness in reducing alcohol-related driving fatalities.
While we have made progress, drinking and driving still claims
about 15,000 lives annually. A variety of public policies, including law
enforcement, prevention, and treatment efforts aimed at decreasing this
unacceptably high rate, are being implemented by the States. Findings from
research can provide information on which of these efforts, individually or in
combination, are most effective in reducing drinking and driv-ing. For example,
although license revocation combined with treatment has been shown to be
effective in preventing repeat drinking and driving offenses, we do not yet know
specifically which types of treatment are the most effective with which types of
offenders.
References
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elimination of alcohol: Highway safety aspects. Journal of Studies on
Alcohol (Suppl. 10):98-108, July 1985. (2) Voas, R.B., & Lacey,
J.H. Drunk driving enforcement, adjudication, and sanctions in the United
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Advances in Research and Prevention. New York: Guilford Press, 1990. pp.
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All material contained in the Alcohol Alert is in the
public domain and may be used or reproduced without permission from NIAAA.
Citation of the source is appreciated.
Copies of the Alcohol Alert are
available free of charge from the Scientific Communications Branch, Office of
Scientific Affairs, NIAAA, Willco Building, Suite 409, 6000 Executive Boulevard,
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