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Alcohol and Transportation Safety
Research has shown that even low blood
alcohol concentration (BAC)1 impairs driving
skills and increases crash risk. New
information about BAC and impairment has led
to policy changes, which have contributed to
declines in alcohol-related crashes and
fatalities. This paper examines some aspects
of alcohol-induced impairment and reviews
selected strategies designed to reduce
alcohol-related crashes and repeat
drinking-and-driving offenses.
BAC and Impairment
A review of 112 studies concluded that
certain skills required to operate
essentially any type of motorized vehicle
become impaired at even modest departures
from zero BAC. At 0.05 percent BAC, most
studies reported significant impairment. By
0.08 percent BAC, 94 percent of the studies
reported impairment. Some skills are
significantly impaired at 0.01 percent BAC,
although other skills do not show impairment
until 0.06 percent BAC (1). At BACs of 0.02
percent or lower, the ability to divide
attention between two or more sources of
visual information can be impaired. Starting
at BACs of 0.05 percent, drivers show other
types of impairment, including eye movement,
glare resistance, visual perception, and
reaction time. Moskowitz and colleagues (2)
reported that alcohol significantly impaired
driving simulator performance at all BACs
starting at 0.02 percent.
The risk of a fatal crash for drivers with
positive BACs compared with other drivers
(i.e., the relative risk) increases with
increasing BAC, and the risks increase more
steeply for drivers younger than age 21 than
for older drivers (3). Between 0.08 and 0.10
percent BACs, the relative risk of a fatal
single-vehicle crash varies between 11
percent (for drivers age 35 and older) and
52 percent (for male drivers ages 16-20).
Other forms of transportation also have been
investigated. Studies using an automated
device that simulates actual flight
conditions have shown pilot performance to
be impaired at BACs as low as 0.04 percent
(4,5) and to remain impaired for as long as
14 hours after pilots reached BACs between
0.10 percent and 0.12 percent (4,6). Another
experiment using a simulated environment
showed that experienced maritime academy
students with BACs of 0.05 needed
significantly more time than did other
students to solve a problem related to power
plant operation on board a merchant ship and
were not aware of their impairment (7).
Factors That Influence Alcohol-Induced
Impairment
Alcohol Tolerance. Research suggests that
the repeated performance of certain tasks
while under the influence of alcohol can
make a person less sensitive to impairment
at a given BAC. However, although impairment
from alcohol may not be evident during
routine tasks, performance would worsen in
novel or unexpected situations (8).
Age. Based on miles driven, the highest
driver fatality rates are found among the
youngest and oldest drivers. Compared with
the fatality rate for drivers ages 25-69,
the rate for 16- to 19-year-old drivers is
about four times as high, and the rate for
drivers age 85 and older is nine times as
high (9,10). Among male drivers younger than
age 21, a BAC increase of 0.02 percent more
than doubles the relative risk for a
single-vehicle fatal crash. Women in this
age group, however, have lower relative risk
than do men at every BAC (3). Young drivers'
greater crash risk is attributed, in part,
to lack of driving experience (11) coupled
with overconfidence (12). The presence of
other teenagers in the car may encourage
risky driving and is associated with
increased fatal crash risk among young
drivers (13).
Alcohol is less often a factor in crashes
involving older drivers. In 1999 drivers age
65 and older killed in crashes were the
least likely of any adult age group to have
positive BACs (14). Nevertheless, a person's
crash risk per mile increases starting at
age 55 and exceeds that of a young,
beginning driver by age 80 (15). Factors
associated with unsafe driving include
problems with vision, attention, perception,
and cognition (16,17). Older drivers with
alcoholism also are more vulnerable than are
other elderly drivers to impairment and have
greater crash risks (15).
Sleep Deprivation. Drowsiness increases
crash risk, and research shows that BACs as
low as 0.01 percent increase susceptibility
to sleepiness (1). Alcohol consumption also
increases the adverse effects of sleep
deprivation. Subjects given low doses of
alcohol following a night of reduced sleep
perform poorly in a driving simulator, even
with no detectable alcohol in the blood
(18,19).
Success can be achieved through
drug intervention,
drug rehabilitation
and entering
drug treatment.
Recent Declines in Drinking and Driving
Research shows that drinking and driving in
the United States has decreased over the
past decade, especially among young drivers.
The proportion of all traffic fatalities
that are alcohol related has decreased. The
overall percentage of drivers with positive
BACs among all drivers surveyed on weekend
nights also has decreased. In addition,
crash statistics and driver surveys both
show decreases in the proportion of drivers
with BACs of 0.10 percent or higher, with
the largest decreases among drivers younger
than age 21 (20,21).
Prevention Strategies
Raising the Minimum Legal Drinking Age (MLDA).
The National Highway Traffic Safety
Administration (NHTSA) estimates that
raising the MLDA to 21 has reduced traffic
fatalities involving 18- to 20-year-old
drivers by 13 percent and has saved an
estimated 19,121 lives since 1975. Twenty of
twenty-nine studies conducted between 1981
and 1992 reported significant decreases in
traffic crashes and crash fatalities
following an increase in MLDA. Three studies
found no change in traffic crashes involving
youth in various age groups, and six studies
had mixed results (22). Laws that prohibit
selling or providing alcohol to minors
generally are not well enforced, but
community efforts to increase MLDA
enforcement can be effective (23,24).
Zero-Tolerance Laws. These laws, which set
the legal BAC limit for drivers younger than
age 21 at 0.00 or 0.02 percent, have been
associated with 20 percent declines in the
proportion of drinking drivers involved in
fatal crashes who are younger than age 21
(25) and in the proportion of
single-vehicle, nighttime fatal crashes
among drivers younger than age 21 (26).
Based on driver surveys, researchers have
reported that young drivers may be more
successful than are older drivers in
separating drinking from driving, and these
researchers have suggested that this
difference could be attributable to
zero-tolerance laws (27).
BAC Laws That Lower Limits to 0.08 percent.
The majority of States are now considering
lowering the legal BAC limit for
noncommercial drivers age 21 and older to
0.08 percent. In fact, according to NHTSA,
27 States have now approved legislation to
lower BAC limits to 0.08 percent. Laws
lowering the legal BAC limit for adult
drivers to 0.08 percent are associated with
declines in alcohol-related fatal crashes.
One national study reported that States with
0.08 laws had smaller proportions of adult
drivers in fatal crashes with BACs of
0.01-0.09 percent and with BACs of 0.10
percent and higher (28).
Lower BAC Limits for DUI Offenders and
Transportation Workers. In Maine, a law
lowering the legal BAC limit to 0.05 percent
for anyone convicted of driving under the
influence (DUI) has been found to reduce
significantly the number of fatal crashes
among this population (29). Because drinking
and driving by transportation workers
threatens public safety, the Federal
Government prohibits commercial truck
drivers, railroad and mass transit workers,
maritime employees, and aircraft pilots from
operating their vehicles with BACs of 0.04
percent or higher.
Communitywide Prevention.
Comprehensive community initiatives to
reduce drinking and driving combine the
efforts of public agencies and private
citizens in implementing strategies,
including media campaigns, police training,
high school and college prevention programs,
and increased liquor outlet surveillance.
Such strategies have been found to reduce
fatal crashes, alcohol-related fatal
crashes, and traffic injuries (30,31).
A community program in San Diego was
implemented to reduce the binge drinking and
impaired driving that result when young
people cross the U.S.-Mexico border to drink
in Tijuana, where the legal drinking age is
18 and beverage prices are lower.
Researchers estimated that more than 250
drivers with BACs of 0.08 percent or higher
on U.S. roads every Friday and Saturday
night are border-crossers (32). Targeted
enforcement was found to reduce the number
of late-night crossers by 26 percent (33).
Alcohol Screening and Brief Intervention for
Emergency Room Patients. Emergency
room patients injured in alcohol-related
crashes may have an increased motivation to
change their drinking behavior (34).
Emergency room interventions have been shown
to reduce future drinking and trauma
re-admission (35) as well as drinking and
driving, traffic violations, alcohol-related
injuries, and alcohol-related problems among
18- and 19-year-olds (36).
Reducing Repeated DUI Offenses
License Suspension. Laws that allow for
administrative license suspension (ALS) at
the time of arrest have been found to reduce
both alcohol-related fatal crashes (28,37)
and repeat DUI offenses (38). A study of an
Ohio ALS law found that first-time and
repeat DUI offenders who had their licenses
immediately confiscated had significantly
lower rates of DUI offenses, moving
violations, and crashes during the next 2
years compared with DUI offenders convicted
before the ALS law went into effect (38).
Although research shows that license
suspension reduces repeat DUI offenses,
there is also evidence that up to 75 percent
of suspended drivers continue to drive.
Evaluation of Oregon's "zebra sticker" law
suggests that marking the license plates of
vehicles driven by unlicensed drivers deters
both driving while suspended (DWS) and DUI
by suspended drivers. A similar law in
Washington State was enforced differently
and had no effect (39).
Vehicle Impoundment/Immobilization. Two
studies of an Ohio law that allowed for
vehicle immobilization (40) or impoundment
(41) for multiple DUI offenders both found
that offenders whose vehicles were
immobilized or impounded had lower
recidivism rates compared with other
offenders while their vehicles were not
available and after they were returned.
Other Prevention Strategies. Alcohol
ignition interlocks-breath-testing devices
designed to prevent operation of a vehicle
if the driver's BAC is above a predetermined
low level-are used in some jurisdictions as
an alternative to full license suspension.
Research suggests that offenders who have
interlocks installed have lower recidivism
rates while the device is in use, but that
recidivism rates rise after interlock
removal (42,43). Conversely, a few studies
have reported that recidivism was
significantly reduced both during interlock
installation and after removal (44,45).
At victim impact panels,
drinking-and-driving offenders must listen
to persons who were injured or who lost a
loved one in an alcohol-related crash
recount the event's impact on their lives.
The effects of victim impact panels on
recidivism have been mixed (46-48).
Alcohol and Transportation Safety-A
Commentary by
NIAAA Director Enoch Gordis, M. D.
At what blood alcohol level (BAC) are
individuals too impaired to drive a car
safely? In the United States, the BAC limit
for driving a car in many States is 0.10
percent. The United States, in fact, is the
only industrialized nation to have a BAC
limit this high. A large body of creditable
research over many years has clearly shown
that impairment of tasks necessary for safe
driving begins at levels as low as 0.05
percent. At the 0.08 percent BAC level,
currently under consideration in many
States, individuals are significantly
impaired and at risk for causing harm to
themselves and others. To date, 27 States
have lowered the legal BAC limit to 0.08
percent. In many of the States that still
maintain the higher 0.10 percent BAC,
debates about lowering it often have had
little to do with scientific soundness
focusing, instead, on arguments that lower
BAC limits infringe on the public's right to
drink socially. This argument has no merit;
a 160-pound man generally will have reached
only a BAC of approximately 0.04 percent 1
hour after consuming two 12-ounce beers or
two other standard drinks on an empty
stomach. Until these debates consider the
actual, rather than the perceived, results
of lowered BACs, we all run the risk of
being injured or killed in automobile
crashes due to drivers who are significantly
but not legally impaired.
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