National Institute on Alcohol
Abuse and Alcoholism No. 52 April 2001
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 Alcohol Alert 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).
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).