Highway Safety: Effectiveness of State .08 Blood Alcohol Laws (Letter
Report, 06/23/1999, GAO/RCED-99-179).
Most states make it illegal for someone to drive with a blood alcohol
concentration (BAC) of .10--the level at which a person's blood contains
1/10th of one percent alcohol. However, 16 states have more stringent
laws setting the limitation at .08 BAC. In 1998, the Clinton
administration endorsed a bill that would have required all states to
enact and enforce .08 BAC laws or face cuts in federal highways funds.
GAO found that the evidence does not conclusively establish that .08 BAC
laws, by themselves, reduce the number and the severity of
alcohol-related crashes. There are, however, strong indications that .08
BAC laws, in combination with other drunk driving laws (particularly
license revocation laws), sustained public education and information
efforts, and vigorous and consistent enforcement can save lives. Until
recently, only four published studies examined the effectiveness of BAC
laws in five states, and, although the National Highway Traffic Safety
Administration characterized the studies as conclusively establishing
that .08 BAC laws by themselves were effective, the studies had
limitations. In April 1999, three additional studies were released that
were more comprehensive and showed many positive results but also fell
short of providing conclusive evidence that .08 BAC laws were, by
themselves, responsible for reducing alcohol-related crashes and
fatalities.
--------------------------- Indexing Terms -----------------------------
REPORTNUM: RCED-99-179
TITLE: Highway Safety: Effectiveness of State .08 Blood Alcohol
Laws
DATE: 06/23/1999
SUBJECT: Alcohol abuse
Motor vehicle safety
Highway safety
State law
Law enforcement
Accident prevention
Traffic violations
Traffic accidents
IDENTIFIER: NHTSA Fatal Accident Reporting System
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Cover
================================================================ COVER
Report to Congressional Committees
June 1999
HIGHWAY SAFETY - EFFECTIVENESS OF
STATE .08 BLOOD ALCOHOL LAWS
GAO/RCED-99-179
Highway Safety and .08 Blood Alcohol Laws
(348125)
Abbreviations
=============================================================== ABBREV
BAC - blood alcohol concentration
DOT - Department of Transportation
FARS - Fatal Accident Reporting System
NHTSA - National Highway Traffic Safety Administration
Letter
=============================================================== LETTER
B-280883
June 23, 1999
The Honorable John McCain
Chairman
The Honorable Ernest F. Hollings
Ranking Minority Member
Committee on Commerce, Science,
and Transportation
United States Senate
The Honorable Bud Shuster
Chairman
The Honorable James L. Oberstar
Ranking Democratic Member
Committee on Transportation and Infrastructure
House of Representatives
In 1997, someone in the United States died in an alcohol-related
motor vehicle crash every 32 minutes. For years, the Congress and
the states have grappled with and sought solutions to the problem of
drunk driving. Most states have laws making it illegal for people to
drive with a specified level of alcohol in their blood, usually set
at .10 blood alcohol concentration (BAC)--the level at which a
person's blood contains 1/10th of 1 percent alcohol. However, 16
states have more stringent laws setting the limit at .08 BAC. In
1998, the Clinton administration endorsed a bill that would have
required all states to enact and enforce .08 BAC laws or face
reductions in federal highway funds. The Senate approved this bill;
the House took no action.
The Transportation Equity Act for the 21st Century directed GAO to
evaluate the effectiveness of state .08 BAC laws in reducing the
number and severity of crashes involving alcohol.\1 To accomplish
this objective, we reviewed (1) the policies and positions of the
Department of Transportation's (DOT) National Highway Traffic Safety
Administration (NHTSA) on .08 BAC laws and other drunk driving
countermeasures and (2) seven published studies on the effect of .08
BAC laws on the number and severity of crashes involving alcohol,
including three studies released on April 28, 1999.
--------------------
\1 The Transportation Equity Act for the 21st Century also directed
us to study the effectiveness of .02 BAC laws for drivers under 21 in
reducing the number and severity of crashes involving alcohol. The
National Highway System Designation Act of 1995 required all states
to enact and enforce such laws or face reductions in federal highway
funds. However, as agreed to by your staff, we will not address the
impact of .02 BAC laws, since all 50 states and the District of
Columbia now have laws establishing BAC levels of .02 or less for
drivers under 21.
RESULTS IN BRIEF
------------------------------------------------------------ Letter :1
Overall, the evidence does not conclusively establish that .08 BAC
laws, by themselves, result in reductions in the number and severity
of alcohol-related crashes. There are, however, strong indications
that .08 BAC laws in combination with other drunk driving laws
(particularly license revocation laws), sustained public education
and information efforts, and vigorous and consistent enforcement can
save lives. For example, while two studies have concluded that
California's .08 BAC law was not directly associated with the decline
in drunk driving deaths the state experienced in the early 1990s,
these studies found that the .08 BAC law was effective when paired
with the state's license revocation law, which took effect 6 months
later.
Until recently, only four published studies examined the
effectiveness of .08 BAC laws in five states and, while NHTSA
characterized the studies as conclusively establishing that .08 BAC
laws by themselves were effective, the studies had limitations and
raised methodological concerns calling their conclusions into
question or reported mixed results. In April 1999, three additional
studies were released that were more comprehensive and showed many
positive results but nevertheless fell short of providing conclusive
evidence that .08 BAC laws were, by themselves, responsible for
reductions in alcohol-related crashes and fatalities. It is
difficult to accurately predict how many lives would be saved if all
states enacted .08 BAC laws because whether a state sees reductions
after enacting a .08 BAC law depends on a number of factors,
including the degree to which the law is publicized, how well it is
enforced, other drunk driving laws in effect, and public attitudes
concerning alcohol. Despite the absence of a strong causal link
between .08 BAC laws by themselves and reductions in traffic
fatalities, other evidence, including medical evidence on drivers'
impairment, should be considered when evaluating the effectiveness of
.08 BAC laws.\2
--------------------
\2 Because the Transportation Equity Act for the 21st Century
directed us to review the effectiveness of .08 BAC laws in reducing
the number and severity of crashes involving alcohol, we did not
evaluate the medical impairment evidence.
BACKGROUND
------------------------------------------------------------ Letter :2
It is illegal in every state and the District of Columbia to drive a
motor vehicle while under the influence of alcohol. In addition, all
states but two have blood alcohol per se lawslaws that make it
unlawful for a person to drive a motor vehicle with a specific amount
of alcohol in his or her blood. As figure 1 shows, 32 states and the
District of Columbia have set that amount at .10 BAC. In 16 states,
the per se limit is 20 percent lower, or .08 BAC.
Figure 1: State Blood Alcohol
Per Se Laws
(See figure in printed
edition.)
Note: States with .08 BAC laws are shown with the year the law
became effective.
Source: GAO's illustration based on information from NHTSA.
On average, according to NHTSA, a 170-pound man reaches .08 BAC after
consuming five 12-ounce beers (4.5-percent alcohol by volume) over a
2-hour period. A 120-pound woman reaches the same level after
consuming three beers over the same period. NHTSA publishes a BAC
estimator that computes the level of alcohol in a person's blood on
the basis of the person's weight and gender and the amount of alcohol
consumed over a specified period of time. This estimator assumes
average physical attributes in the populationin reality, alcohol
affects individuals differently, and this guide cannot precisely
predict its effect on everyone. For example, younger people have
higher concentrations of body water than older people; therefore,
after consuming the same amount of alcohol, a 170-pound 20-year-old
man attains a lower BAC level on average than a 170-pound 50-year-old
man.
As figure 2 illustrates, NHTSA's estimator shows that the difference
between the .08 BAC and .10 BAC levels for a 170-pound man is one
beer over 2 hours. The difference between the .08 BAC and .10 BAC
levels for a 120-pound woman is one-half a beer over the same time
period.
Figure 2: Alcohol Consumption
and Blood Alcohol Levels
(See figure in printed
edition.)
Source: GAO's illustration based on NHTSA's BAC estimator.
Alcohol use is a significant factor in fatal motor vehicle crashes.
In 1997, the most recent year for which data are available, there
were 16,189 alcohol-related fatalities, representing 38.6 percent of
the nearly 42,000 people killed in fatal crashes that year. In the
states with .08 BAC laws, alcohol was involved in 36 percent of all
traffic fatalities, lower than the national average and the
39.5-percent rate of alcohol involvement in the rest of the states.\3
Utah had the lowest level at 20.6 percent; the District of Columbia
had the highest at 58.5 percent. Among the 10 states with the lowest
levels of alcohol-related fatalities, 3 were states with .08 BAC laws
and 7 were states with .10 BAC laws. Among the 10 states with the
highest levels of alcohol-related fatalities, 2 were states with .08
BAC laws, 7 were states with .10 BAC laws, and 1 had no BAC per se
law.
Although alcohol use remains a significant factor in fatal crashes,
fatalities involving alcohol have declined sharply over the last 15
years. In 1982, 25,165 people died in crashes involving alcohol,
57.3 percent of the nearly 44,000 traffic fatalities that year. The
proportion of fatal crashes that involved alcohol declined during the
1980s, falling below 50 percent for the first time in 1989. The
involvement of alcohol in fatal crashes declined markedly in the
early 1990s, from about 50 percent of the fatal crashes in 1990 to
nearly 40 percent in 1994. During this time, the number of people
killed in crashes involving alcohol declined by around 25 percent.
The proportion of fatalities involving alcohol rose slightly in the
next 2 years before falling, in 1997, to its lowest level since 1982,
as figure 3 shows.
Figure 3: Alcohol-Related
Fatalities, 1982-97
(See figure in printed
edition.)
Source: GAO's illustration based on NHTSA's Traffic Safety Facts,
1997.
Each state reports, and NHTSA collects and publishes, data on fatal
crashes through the Fatal Accident Reporting System (FARS), a
comprehensive national database of all crashes in which a person dies
within 30 days of the crash. These data include (1) the number of
fatalities that occur in all crashes and (2) the number of drivers
involved in fatal crashes. FARS also includes whether crashes
involved drivers who had been drinking. However, FARS has
limitations regarding alcohol involvement in crashes--for example,
fewer than half of the drivers at the scene of fatal accidents are
tested for alcohol. To address the missing data, NHTSA developed a
statistical model, first used in 1982, to estimate alcohol
involvement in cases in which data are not available. The model
provides estimates in three broad categories--sober (.00 BAC), low
BAC (.01- .09 BAC), and high BAC (.10 BAC and above).\4 Therefore,
certain questions--such as how many fatal crashes involve drivers
with .08 BAC levels versus other levels or what the average BAC of
drunk drivers involved in fatal crashes is--cannot be reliably
answered by this model. NHTSA plans to release a new model in 1999
that will estimate specific BAC levels.
--------------------
\3 This analysis excludes Idaho and Illinois, states that had .08 BAC
laws take effect during 1997.
\4 When cataloguing fatalities in crashes in which more than one
driver had been drinking, FARS uses the driver with the higher BAC.
NHTSA BELIEVES ALL STATES
SHOULD HAVE ALCOHOL DETERRENCE
MEASURES, INCLUDING .08 BAC
LAWS
------------------------------------------------------------ Letter :3
NHTSA believes that the best countermeasure against drunk driving is
a combination of laws, public education, and enforcement. Since
1970, NHTSA has espoused a systems approach to reducing drunk
driving including enforcement, judicial, legislative, licensing, and
public information components. In 1997, NHTSA published an action
plan developed with other participants to reduce alcohol-related
driving fatalities to 11,000 by the year 2005. This plan recommended
that all states pass a wide range of laws, including ones
establishing .08 BAC limits, license revocation laws--under which a
person deemed to be driving under the influence has his or her
driving privileges suspended or revoked, comprehensive screening and
treatment programs for alcohol offenders, vehicle impoundment, zero
tolerance BAC and other laws for youth, and primary enforcement laws
for safety belts.\5 The plan also called for increased public
awareness campaigns, with an emphasis on target populations such as
young people and repeat offenders. Similarly, The Presidential
Initiative for Making .08 BAC the National Legal Limit, published by
NHTSA in August 1998, contained a four-point plan that recommended
the expansion of public education campaigns; the building of
public-private partnerships; and active, high-visibility enforcement
of several alcohol laws.
The value of public education and enforcement has been demonstrated
in a number of studies. A recent NHTSA evaluation of a sobriety
checkpoint program in Tennessee, a state with a .10 BAC limit,
concluded that the program and its attendant publicity reduced
alcohol-related fatal accidents in that state by 20.4 percent. A
systems approach to traffic safety is not limited to preventing drunk
driving. Our January 1996 report concluded that the states that have
been most successful at increasing safety belt use among all drivers
are the ones with primary enforcement laws, visible and aggressive
enforcement, and active public information and education programs.\6
Since 1992, when it first recommended in a report to the Congress
that all states have .08 BAC laws, NHTSA's position has changed from
urging the states to pass .08 BAC laws to favoring that states be
required to do so. The latter position was embodied in the
President's endorsement of a Senate bill entitled the Safe and Sober
Streets Act. This bill would have required all states to enact and
enforce .08 BAC laws by October 1, 2001, or lose 5 percent of certain
federal highway funds the first year and 10 percent each succeeding
year. The Senate approved this bill on March 4, 1998, but the House
took no action before the 105\th Congress adjourned.\7
As figure 4 shows, NHTSA has a number of reasons why it believes all
states should adopt .08 BAC laws.
Figure 4
NHTSA's Reasons Why All States Should
Adopt .08 BAC Laws
----------------------------------------------------------------------
Virtually all drivers are substantially impaired at .08 BAC with
regard to critical driving tasks.
The risk of being in a crash increases substantially when a driver
reaches .08 BAC.
.08 is a reasonable level to set the limit.
The public supports lower BAC limits.
Other industrialized nations have .08 or lower BAC laws.
Lowering the limit to .08 is a proven effective countermeasure that
will reduce crashes and save lives.
----------------------------------------------------------------------
One of NHTSA's principal arguments for nationwide adoption of .08 BAC
laws is that the medical evidence of drivers' impairment at that
level is substantial and conclusive. According to NHTSA, and as
shown in figure 5, reaction time, tracking and steering, and
emergency responses are impaired at even low levels, and
substantially impaired at .08 BAC. As a result, the risk of being in
a motor vehicle crash increases when alcohol is involved, and
increases dramatically at .08 BAC and higher levels. In contrast to
NHTSA's position, industry associations critical of .08 BAC laws
contend that .08 BAC is an acceptable level of impairment for driving
a motor vehicle and that these laws penalize responsible social
drinking. These associations also believe that .08 BAC laws do not
address the problem of drunk driving because many more drivers using
alcohol are reported at the high BAC levels (above .10 BAC) than
the lower BAC levels. Because we were directed to review the impact
of .08 BAC laws on the number and severity of crashes involving
alcohol, we did not review the medical evidence on impairment or
other arguments in favor of or in opposition to .08 BAC laws.
Figure 5: NHTSA's Position on
Medical Evidence of Drivers'
Impairment
(See figure in printed
edition.)
Source: GAO's illustration based on information from NHTSA.
NHTSA also believes that lowering the BAC limit to .08 is a proven
effective measure that will reduce the number of crashes and save
lives. For example, in a December 1997 publication, NHTSA stated
that recent research . . . has been quite conclusive in showing
the impaired driving reductions already attributable to .08, as well
as the potential for saving additional lives if all states adopted
.08 BAC laws (emphasis added). In May 1998, the NHTSA Administrator
stated, The traffic safety administration is aware of four published
studies, . . . [and] each study has shown that lowering the
illegal blood alcohol limit to .08 is associated with significant
reductions in alcohol-related fatal crashes. In a fact sheet
distributed to state legislatures considering these laws, NHTSA
stated that the agency's analysis of five states that lowered the
BAC limit to .08 showed that significant decreases in alcohol-related
fatal crashes occurred in four out of the five states as a result of
the legislation (emphasis added). NHTSA used these study results to
encourage states to enact .08 BAC laws, testifying in one instance
before a state legislature, We conservatively project a 10-percent
reduction in alcohol-related crashes, deaths, and injuries in the
state.
--------------------
\5 Primary enforcement laws permit officials to enforce safety belt
requirements independently of other traffic safety laws, in contrast
to secondary enforcement laws, which allow officials to enforce
safety belt requirements only when other traffic safety laws are
being enforced.
\6 Motor Vehicle Safety: Comprehensive State Programs Offer Best
Opportunity for Increasing Use of Safety Belts (GAO/RCED 96-24, Jan.
3, 1996).
\7 The Senate approved this bill as an amendment to its surface
transportation reauthorization bill. However, these provisions were
not included in the House bill and were not included in the final
version of the Transportation Equity Act for the 21st Century.
SEVEN STUDIES HAVE EXAMINED THE
EFFECTIVENESS OF .08 BAC LAWS
------------------------------------------------------------ Letter :4
Seven studies have been published assessing the effect of .08 BAC
laws on motor vehicle crashes and fatalities in the United States.
Four studies published between 1991 and 1996 assessed the
effectiveness of .08 BAC laws in the five states that enacted them
between 1983 and 1991. On April 28, 1999, NHTSA released three
additional studies. Table 1 summarizes the seven studies that
examine .08 BAC laws.
Table 1
Studies on the Effectiveness of .08 BAC
Laws
Title of study Released Conducted by Funded by Scope
----------------- ------------ ---------------- ------------------ ------------------
The Effects 1991 Research and NHTSA California
Following the Evaluation
Implementation of Associates
an .08 BAC Limit
and an
Administrative
Per Se Law in
California
A Preliminary 1994 NHTSA staff NHTSA California, Utah,
Assessment of the Oregon, Maine, and
Impact of Vermont
Lowering the
Illegal BAC Per
Se Limit to .08
in Five States
The General 1995 Department of California Office California
Deterrent Impact Motor Vehicles, of Traffic Safety
of California's State of
.08% Blood California
Alcohol
Concentration
Limit and
Administrative
Per Se License
Suspension Laws
Lowering State 1996 Researchers from Grants, including California, Utah,
Legal Blood Boston ones from the Oregon, Maine, and
Alcohol University's National Institute Vermont
Concentration School of Public on Alcohol Abuse
Limits to .08%: Health and Alcoholism and
The Effect on the U.S. Centers
Fatal Motor for Disease
Vehicle Crashes Control and
Prevention
The Effects of 1999 Rainbow NHTSA California, Utah,
0.08 Laws Technology Inc., Oregon, Maine,
and NHTSA's Vermont, New
National Center Hampshire, North
for Statistics Carolina, Kansas,
and Analysis New Mexico,
Florida, and
Virginia.
Evaluation of the 1999 University of NHTSA North Carolina
Effects of North North Carolina
Carolina's 0.08%
BAC Law
The Relationship 1999 Pacific NHTSA 50 states and the
of Alcohol Safety Institute for District of
Laws to Drinking Research and Columbia
Drivers in Fatal Evaluation
Crashes
-----------------------------------------------------------------------------------------
THE FIRST FOUR PUBLISHED
STUDIES HAD LIMITATIONS AND
RAISED METHODOLOGICAL
CONCERNS
---------------------------------------------------------- Letter :4.1
Although NHTSA characterized the first four studies on the
effectiveness of .08 BAC laws as conclusively establishing that .08
BAC laws resulted in substantial reductions in fatalities involving
alcohol, we found that three of the four studies had limitations and
raised methodological concerns that called their conclusions into
question. For example, while a NHTSA-endorsed Boston University
study concluded that 500 to 600 fewer fatal crashes would occur each
year if all states adopted .08 BAC laws, this study has been
criticized for, among other reasons, its method of comparing states;
and a recent NHTSA study characterized the earlier study's conclusion
as unwarranted. The fourth study reported mixed results.
Therefore, these studies did not provide conclusive evidence that .08
BAC laws by themselves have resulted in reductions in drunk driving
crashes and fatalities. A task force of the New Jersey State Senate
examined this evidence and, in a report issued in December 1998,
reached a similar conclusion.\8
--------------------
\8 State of New Jersey, Senate Task Force on Alcohol-Related Motor
Vehicle Accidents and Fatalities, Dec. 11, 1998. Created by the
leaders of the New Jersey State Senate, the task force was composed
of elected officials and representatives from the state's judicial,
medical, academic, and law enforcement communities. The task force
was charged with, among other things, evaluating the available
studies, and determining whether reducing the BAC limit to .08 would
reduce the number of alcohol-related accidents and fatalities in New
Jersey. The task force concluded that the impact of laws that
reduce the per se BAC level from .10 to .08, in isolation, is
inconclusive and that the effect of public education and awareness
campaigns and license revocation laws can be greater than changing
the legal BAC."
THE CALIFORNIA STUDIES
-------------------------------------------------------- Letter :4.1.1
NHTSA has cited California's experience as evidence of the
effectiveness of .08 BAC laws. For example, in a publication
promoting the need for .08 BAC laws, NHTSA stated that
alcohol-related fatalities significantly decreased after the state's
BAC limit was lowered to .08 in 1990. In another publication, it
said California's .08 law was analyzed by NHTSA, [and] . . . the
state experienced a 12% reduction in alcohol-related fatalities,
although some of this can be credited to the new administrative
license revocation law.
While NHTSA's 1991 study by Research and Evaluation Associates (see
table 1) did find a 12-percent decline in alcohol-related fatalities
after the .08 BAC law took effect, the study had important
limitations. For example, the authors had available to them only 1
year of data for the period after the law went into effect, an
unusually short period of time to analyze trends, and the authors
acknowledged this limitation. California also had a license
revocation law--under which a person deemed to be driving under the
influence has his or her driving privileges suspended or revokedtake
effect 6 months after the .08 BAC law. Although the authors
concluded that this law had no effect, they stated that they were
unable to accurately account for the separate effects of the two
laws.
A more comprehensive, methodologically sound study of California was
released by the state's Department of Motor Vehicles in 1995. In
contrast to the 1991 review, this study was based on 4 years of data
after the law became effective and found mixed results. The study
concluded that the .08 BAC law was not associated with any
statistically significant reductions in crashes resulting in
fatalities or serious injuries in which drivers were reported to have
been drinking, but that reductions did occur in accidents that took
place during hours in which alcohol involvement is probable, such as
nighttime crashes between 2 and 3 a.m. The study found reductions
associated with the state's license revocation law--a 9 to 13 percent
decline in crashes resulting in fatalities or serious injuries in
which drivers were reported to have been drinking. However, given
the 6-month time period separating the effective dates of the two
laws, the authors concluded that .08 BAC and license revocation laws
most likely worked together to lower fatalities.
Although the 1995 study was more comprehensive than the 1991 study,
NHTSA's public statements and literature often quote the 12-percent
reduction cited in the 1991 study and rarely refer to the 1995 study.
California continued to experience a decline in alcohol-related
fatalities through the 1990s--from 47 percent of fatalities in 1991
to 36 percent in 1997. California traffic safety and law enforcement
officials believe that this progress is attributable to the
combination of stronger laws, a sustained public information
campaign, and vigorous enforcement.
THE BOSTON UNIVERSITY
STUDY
-------------------------------------------------------- Letter :4.1.2
A 1996 study by researchers from the Boston University School of
Public Health published in the American Journal of Public Health
compared the first five states to adopt .08 BAC laws with five
nearby states that retained .10 BAC laws. It found a 16 percent
greater decline in the proportion of alcohol-related fatalities among
drivers in the states adopting the lower limit and concluded that if
all states adopted .08 BAC laws, 500 to 600 fewer fatal crashes would
occur annually. These study results were endorsed by NHTSA and often
cited in the agency's literature and public statements. President
Clinton cited the study in a March 1998 statement and said . . .
if all states lower their BAC to .08, it will result in 600 fewer
alcohol-related deaths each year.
However, this study has been criticized by many traffic safety
experts both inside and outside of NHTSA and has methodological
limitations that call its results into question. For example:
-- Many traffic safety experts question this study's method of
comparing one state to another. The study does not explain the
criteria used to select the comparison states. Using one state
as a control to assess the impact of a new law in another state
assumes that all other conditions are held equal except for the
introduction of the law. One critic noted, for example, that
one of the states with a .08 BAC law employs random roadside
sobriety checkpoints and was compared to a state with a .10 BAC
law that prohibits the practice. Changing the selection of
comparison states can dramatically change this study's results.
According to NHTSA, while other traffic safety studies have made
single state comparisons, it is best to compare one state to
several or to the rest of the nation.
-- Three of the five states had license revocation laws take effect
within 10 months of their .08 BAC laws. This study made no
effort to separately analyze the relative contribution of the
two types of laws to any subsequent decline in fatal motor
vehicle crashes in those three states. Thus, in at least three
states, the authors' findings could as easily apply to the
license revocation law as the .08 BAC law. The authors
acknowledged this limitation, but it is rarely cited in NHTSA's
literature and public statements endorsing this study and its
findings.
-- The study's conclusion that 500 to 600 fewer fatal crashes would
occur annually if all states had .08 BAC laws is unfounded. The
study does not explain how this estimate was derived or how the
reduction could be credited to .08 BAC laws since the .08 BAC
and license revocation laws went into effect within 10 months of
each other in three of the five states. The authors told us
that the estimate assumed that all states without .08 BAC laws
would experience a reduction of up to 10 percent in
alcohol-related crashes after enacting the laws. However, the
study provides no basis for assuming that reductions of that
magnitude would occur. Even this particular study found that
while three of the five states experienced reductions greater
than their comparison state, two of the five did not. NHTSA's
April 1999 study of the effect of .08 BAC laws in 11 states (see
table 1) characterized this conclusion as unwarranted.
NHTSA STAFF STUDY
-------------------------------------------------------- Letter :4.1.3
In 1994, NHTSA staff conducted a study that examined FARS data in the
first five states that enacted .08 BAC laws (see table 1). NHTSA has
often cited this study as evidence of the effectiveness of .08 BAC
laws. For example, a December 1997 publication with the National
Safety Council said,
. . . significant reductions in alcohol-related fatal crashes
were found in 4 out of the 5 states ranging from 4% to 40%. . . .
The staff study examined 6 measures of alcohol involvement, ranging
from fatal crashes involving drivers with high BACs to single-vehicle
crashes late at night, in each of the five states (for a total of 30
measures) and found statistically significant decreases in 9 of the
30 measures. The study also had several important limitations, which
the authors acknowledged. For example, as with the Boston University
study, the staff study made no effort to separately account for the
relative contributions of .08 BAC laws and license revocation laws in
the three states that enacted them within a short period. The staff
study cautioned that the results were preliminary and that they
pointed to the need for further research. NHTSA's public statements,
however, were more definitiveconveying, for example, the impression
that fatal crashes involving alcohol went down 40 percent in one of
the five states. However, the 40-percent figure refers to only one
of the six measures in Vermont, a state that experiences fairly
significant year-to-year variations in fatal crashes. One of the
authors told us he viewed the results as indicative of positive but
not clear results.
RECENT STUDIES ARE MORE
COMPREHENSIVE, BUT RESULTS
ARE MIXED
---------------------------------------------------------- Letter :4.2
On April 28, 1999, NHTSA released three studies that it sponsored
(see table 1). These studies are more comprehensive than the earlier
studies and show many positive results but fall short of conclusively
establishing that .08 BAC laws by themselves have resulted in
reductions in alcohol related fatalities. For example, during the
early 1990s, when the involvement of alcohol in traffic fatalities
declined from around 50 percent to nearly 40 percenta trend in
states with both .08 BAC and .10 BAC laws--eight states' .08 BAC laws
became effective, and the recent studies disagree on the degree to
which .08 BAC laws played a role. Two of the studies reached
different conclusions about the effect of one state's .08 BAC
law--one concluded that the law brought about reductions in drunk
driving deaths in North Carolina, while another concluded that the
state's reductions occurred as the result of a long-term trend that
began before the law was enacted. In a statement releasing the three
studies, NHTSA credited the nation's progress in reducing drunk
driving to a combination of strict state laws and tougher enforcement
and stated that these three studies provide additional support for
the premise that .08 BAC laws help to reduce alcohol-related
fatalities, particularly when they are implemented in conjunction
with other impaired driving laws and programs.
ELEVEN-STATE STUDY
-------------------------------------------------------- Letter :4.2.1
An April 1999 NHTSA study of 11 states with .08 BAC laws (see table
1) assessed whether the states experienced statistically significant
reductions in three measures of alcohol involvement in crashes after
the law took effect: (1) the number of fatalities in crashes in
which any alcohol was involved, (2) the number of fatalities in
crashes where drivers had a BAC of .10 or greater (high BAC), and
(3) the proportion of fatalities involving high BAC drivers to
fatalities involving sober drivers. The study performed a similar
analysis for license revocation laws and also modeled and controlled
for any preexisting long-term declining trends these states may have
been experiencing when their .08 BAC laws went into effect. The
study found that 5 of the 11 states had reductions in at least one
measure and that 2 of the 11 states had reductions in all three
measures. Table 2 summarizes the states and measures for which the
study found statistically significant reductions after .08 BAC laws
became effective.
Table 2
Results of the 11-State Study of .08 BAC
Laws
Statistically significant reduction occurred in
-----------------------------------------------------
Proportion of
fatalities
involving
high BAC
Year .08 Fatalities drivers
BAC law Alcohol- involving to those
became related high BAC involving
State effective fatalities drivers sober drivers
---------------- ---------------- ---------------- ---------------- -----------------
Utah 1983 No No No
Oregon 1983 No No No
Maine 1988 No No No
California 1990 No No No
Vermont 1991 Yes Yes Yes
Kansas 1993 No No Yes
North Carolina 1993 No No Yes
Florida 1994 Yes Yes Yes
New Hampshire 1994 No No No
New Mexico 1994 No No Yes
Virginia 1994 No No No
=========================================================================================
Total 2 of 11 2 of 11 5 of 11
-----------------------------------------------------------------------------------------
Note: Yes indicates a statistically significant reduction after
the .08 BAC law became effective. No indicates no statistically
significant reduction.
Reductions in all three measures of fatalities involving alcohol
occurred in Florida and Vermont. Although alcohol involvement in
fatal crashes began to decline in Florida before the .08 BAC law was
enacted, it continued to do so after the law went into effect on
January 1, 1994. According to FARS, the number of alcohol-related
traffic deaths in Florida declined in 1994 by nearly 10 percent,
while the proportion of fatalities involving alcohol fell from 44 to
39 percent--in 1997 it stood at around 34 percent. While the study
noted that Vermont has experienced fluctuations in its fatal crash
rates, it found that after Vermont's .08 BAC law took effect, it also
experienced statistically significant reductions in both the number
of fatalities involving alcohol and the proportion of fatalities
involving drivers with high BACs to those involving sober drivers.
In this study, Vermont was the only state of the first five states to
enact .08 BAC laws that showed any reductions in alcohol-related
fatalities associated with .08 BAC laws.
Three other states that enacted .08 BAC laws in 1993 and 1994North
Carolina, New Mexico, and Kansas--experienced statistically
significant reductions in the proportion of fatalities involving
drivers with high BACs to those involving sober drivers. According
to one of the authors, this proportion is the most accurate indicator
of the study's three measuresthe study noted that if fatalities
involving sober drivers decline along with alcohol-related
fatalities, then some broader cause other than alcohol legislation is
affecting all traffic fatalities. However, if the .08 BAC law
operates as expected, alcohol-related deaths will decline while
deaths involving sober drivers remain unaffected. In Kansas, the
proportion of alcohol involvement declined because fatalities
involving sober drivers increased while alcohol-related fatalities
remained relatively stable, and in North Carolina, fatalities
involving sober drivers increased markedly while fatalities involving
drivers with high and low BACs continued their preexisting downward
trend. The author stated that without the .08 BAC legislation,
alcohol-related fatalities would have been expected to increase along
with fatalities involving sober drivers.
In two states where no statistically significant reductions occurred
after .08 BAC laws became effective in any category--California and
Virginia--the study found that the .08 BAC laws were effective when
paired with the states' license revocation laws. In both cases, the
license revocation laws went into effect after the .08 BAC laws, and
the study found that the reductions did not begin until the license
revocation laws were in force.
Finally, the study found no statistically significant reductions in
four states. Utah experienced no noticeable change in fatalities
involving alcohol after enacting both its .08 BAC and license
revocation laws in 1983. The authors noted that the rate of alcohol
involvement in fatal crashes in Utah was substantially lower than the
national average and that further reductions would have been
difficult. Fatalities involving alcohol in Oregon showed little
change after the .08 BAC law went into effect in 1983the most
dramatic change occurred over 6 years after the law's implementation.
Maine experienced no significant reductions in alcohol-related
fatalities after its .08 BAC law was implemented in 1988. New
Hampshire experienced a decline in alcohol-related fatalities 2 years
before its .08 BAC law went into effect in 1993 but saw no
significant decline in fatalities associated with the .08 BAC law.
The study was careful to not draw a causal relationship between the
reductions it found and the passage of .08 BAC laws by themselves.
Rather, it concluded that .08 BAC laws added to the impact that
enforcement; public information; and legislative activities,
particularly license revocation laws, were having. In addition to
the two states where .08 BAC and license revocation laws were found
to be effective in combination, the study noted that the five states
with .08 BAC laws that showed reductions already had license
revocation laws in place. One of the authors told us that this
suggested that the .08 BAC laws had the effect of expanding the scope
of the license revocation laws to a new portion of the driving
public.
UNIVERSITY OF NORTH
CAROLINA STUDY
-------------------------------------------------------- Letter :4.2.2
A NHTSA-sponsored study by the University of North Carolina
concluded, in contrast to the 11-state study, that the .08 BAC law in
North Carolina had little clear effect. The study examined
alcohol-related crashes and crashes involving drivers with BACs
greater than .10 from 1991 through 1995; compared fatalities among
drivers with BACs greater than .10 in North Carolina with such
fatalities in 11 other states; and compared six measures of alcohol
involvement in North Carolina and 37 states that did not have .08 BAC
laws at that time. The study controlled for and commented on
external factors that could confound the results, such as the state's
sobriety checkpoints, enforcement, and media coverage. The study
found the following:
-- No statistically significant decrease in alcohol-related crashes
after passage of North Carolina's .08 BAC law in three direct
and two proxy measures.\9
-- A continual decline in the proportion of fatally injured drivers
with BACs equal to or greater than .10 but no abrupt change in
fatalities that could be attributed to the .08 BAC law.
-- Decreases in alcohol-related crashes in North Carolina and in
the 11 other states studied. While North Carolina's decreases
were greater, the study concluded that no specific effects could
be attributed to the .08 BAC law.
-- No statistically significant difference between North Carolina
and 37 states without .08 BAC laws in four of the six measures.
While reductions in police-reported and estimated instances of
alcohol involvement were found to be statistically significant,
these reductions happened 18 months before North Carolina
lowered its BAC limit. The authors attributed these decreases,
in part, to increased enforcement.
The study concluded that the .08 BAC law had little clear effect on
alcohol-related fatalities in North Carolina, and that a downward
trend was already occurring before North Carolina enacted its .08 BAC
law and that this trend was not affected by the law. The authors
offered several possible explanations, including that (1) the effects
of the .08 BAC laws were obscured by a broader change in
drinking-driving behavior that was already occurring; (2) North
Carolina had made substantial progress combating drunk driving and
that the remaining drinking and driving population in North Carolina
was simply not responsive to the lower BAC law; and (3) .08 BAC laws
are not effective in measurably affecting the behavior of drinking
drivers.
--------------------
\9 Direct measures are actual observations, such as police reports of
alcohol involvement in crashes, whereas proxy measures are not actual
observations, but categories in which the involvement of alcohol is
considered probable, such as nighttime crashes between 2 and 3 a.m.
50-STATE STUDY
-------------------------------------------------------- Letter :4.2.3
The third April 1999 NHTSA study did a complex regression analysis
assessing the effect of three drunk driving laws, including .08 BAC
laws.\10
It evaluated .08 BAC laws by comparing two groups--states with .08
BAC laws with states with .10 BAC laws, before and after the laws
were passed. The study examined quarterly FARS data for all 50
states and Washington, D.C. from 1982 through 1997 and tested for
reductions in the involvement of (1) low BAC drivers (.01 BAC
through .09 BAC) and (2) high BAC drivers (.10 BAC and above) in
fatal crashes. The study was more comprehensive than the prior
multistate studies, having controlled for the effects of factors such
as the number of licensed drivers, vehicle miles traveled, per capita
beer consumption, unemployment rates, urban/rural composition,
season, safety belt laws, and existing downward trends in
alcohol-related fatal crashes. This study concluded that states that
enacted .08 BAC laws experienced an 8-percent reduction in the
involvement of drivers with both high and low BACs when compared with
the involvement of sober drivers. The study estimated that 274 lives
have been saved in the states that enacted .08 BAC laws and that 590
lives could be saved annually if all states enacted .08 BAC laws.
While more comprehensive than other studies, the study used a method
to calculate the 8-percent reduction that is different, and thus not
directly comparable, to those for fatality estimates reported in
other studies and publications. In particular, this method can
produce a numerical effect that is larger than other methods. In the
past, NHTSA's statistics and other studies measured differences
either (1) in the number of alcohol-related fatalities or the number
of drivers reported to have been using alcohol (termed
alcohol-involved drivers) or (2) in the proportion of such
fatalities or drivers as a percentage of all fatalities or drivers.
The 50-state study's 8-percent estimate is the change in the ratio of
alcohol-involved drivers to sober drivers who are in fatal crashes.
While this is not an inappropriate way to measure differences in
crashes and fatalities, this method can increase the size of the
effect because, rather than comparing fatalities or drivers involving
alcohol to all fatalities or drivers, it compares the number of
alcohol-involved drivers to just the number of sober drivers. This
method produced a larger effect in this study because, since 1982, of
the drivers involved in fatal crashes, the number reported to have
been using alcohol has dramatically declined (by around 39 percent),
while the number reported to have been sober has substantially
increased (by around 25 percent). While the 11-state study also
measured this ratio, that study did not report a numerical effect.
Table 3 illustrates the difference between these methods of
portraying traffic statistics using NHTSA's FARS data on drivers
involved in fatal crashes between 1995 and 1997. As the table shows,
while the number of alcohol-involved drivers declined by about 6
percent, the ratio of such drivers to sober drivers declined by 9
percent.
Table 3
Drivers Involved In Fatal Crashes, 1995-
97
Differen
1995 1997 ce
---------------------------------------- -------- -------- --------
Alcohol-involved drivers 14,269 13,393 (6.1%)
Sober drivers 41,895 43,209 3.1%
All drivers 56,164 56,602 0.8%
Ratio of alcohol-involved drivers to 34% 31% (9%)
sober drivers
----------------------------------------------------------------------
Source: GAO's analysis of FARS data.
Another reason why this study's results cannot be directly compared
to other studies' is because it did not include data for drivers
under 21. In 1997, drivers under 21 accounted for around 14 percent
of the drivers in fatal crashes and about 12 percent of the drivers
in fatal crashes involving alcohol. According to the authors,
drivers under 21 were excluded from the analysis because other laws
affect these drivers, such as minimum drinking age and zero
tolerance BAC laws, and thus the primary effect of .08 BAC
legislation would be expected to be on the population over 21 years
old. While this argument may have merit, other arguments exist for
including this population. First, NHTSA has stated that .08 BAC laws
have a general deterrent effect on drinking and driving among all
drivers. Also, young drivers violating .08 BAC laws have been
prosecuted under those laws without regard to age, suggesting that
these laws do not affect only adults. For example, in California,
13,067 drivers under 21 were convicted under the state's .08 BAC law
in 1997, compared with 11,517 drivers under 21 convicted under the
state's "zero tolerance" BAC law. Finally, with the exception of the
1994 NHTSA staff study, all other studies of the effect of .08 BAC
laws, including the recent 11-state and North Carolina studies, have
included persons under 21 in their analyses.
Including persons under 21 years old would have changed these study
results. In particular, the study would have found no statistically
significant reductions associated with .08 BAC laws for drivers at
low BAC levels. The findings regarding drivers at high BAC levels--a
group that contains over 3 times as many drivers--would have remained
substantially unchanged.
The study warns that it is important to interpret estimates of lives
saved due to any single law with considerable caution. In
particular, as the study notes, factors such as public education,
enforcement, and changes in societal norms and attitudes toward
alcohol have produced long-term reductions in drunk driving deaths
over many years. This study did more to control for extraneous
factors than any of the other multistate studies, but this is
inherently difficult to do, and in this case the authors estimate
that 50 to 60 percent of the reductions in alcohol-related fatalities
are explained by the laws it reviewed and the other factors it
considered, a moderate level for statistical analyses of this type.
Because of the uncertainties, the study's estimate of lives saved is
also expressed as a range--and the number of lives saved in states
with .08 BAC laws could have been as few as 88 or as many as 472.\11
Similarly, if the states without .08 BAC laws enacted them and
experienced reductions comparable to those found in the study, the
number of lives saved annually was projected to be as few as 200 or
as many as 958. While the study reported results for the three laws
it reviewed, including .08 BAC laws, the study also concluded that
the attribution of savings to any single law should be made with
caution since each new law builds to some extent on existing
legislation and on other ongoing trends and activities.
--------------------
\10 Regression analysis is a statistical technique used to describe
and analyze relationships between a dependent variable (e.g. fatal
crashes involving alcohol) and one or more independent variables
(e.g. .08 BAC and license revocation laws).
\11 The study made range estimates at the 95 percent confidence
level, meaning that one would expect these results to occur in 95 out
of 100 cases.
CONCLUSIONS
------------------------------------------------------------ Letter :5
While indications are that .08 BAC laws in combination with other
drunk driving laws as well as sustained public education and
information efforts and strong enforcement can be effective, the
evidence does not conclusively establish that .08 BAC laws by
themselves result in reductions in the number and severity of crashes
involving alcohol. Until recently, limited published evidence
existed on the effectiveness of .08 BAC laws, and NHTSA's
position--that this evidence was conclusive--was overstated. In
1999, more comprehensive studies have been published that show many
positive results, and NHTSA's characterization of the results has
been more balanced. Nevertheless, these studies fall short of
providing conclusive evidence that .08 BAC laws by themselves have
been responsible for reductions in fatal crashes.
Because a state enacting a .08 BAC law may or may not see a decline
in alcohol-related fatalities, it is difficult to accurately predict
how many lives would be saved if all states passed .08 BAC laws. The
effect of a .08 BAC law depends on a number of factors, including the
degree to which the law is publicized; how well it is enforced; other
drunk driving laws in effect; and the unique culture of each state,
particularly public attitudes concerning alcohol.
As drunk driving continues to claim the lives of thousands of
Americans each year, governments at all levels seek solutions. Many
states are considering enacting .08 BAC laws, and the Congress is
considering requiring all states to enact these laws. Although a
strong causal link between .08 BAC laws by themselves and reductions
in traffic fatalities is absent, other evidence, including medical
evidence on impairment, should be considered when evaluating the
effectiveness of .08 BAC laws. A .08 BAC law can be an important
component of a state's overall highway safety program, but a .08 BAC
law alone is not a silver bullet. Highway safety research shows
that the best countermeasure against drunk driving is a combination
of laws, sustained public education, and vigorous enforcement.
AGENCY COMMENTS AND OUR
EVALUATION
------------------------------------------------------------ Letter :6
DOT provided comments on a draft of this report (see app. I). The
Department generally agreed with the information presented in the
report. DOT reiterated its long-standing commitment to a systems
approach for combating drunk driving and stated that while no
individual component, including .08 BAC laws, is effective in
isolation, the overall evidence supports the effectiveness of .08 BAC
laws. DOT stated that the four original studies provided positive,
if not conclusive, results and formed a reasonable basis for
supporting .08 BAC laws. The three recent studies added to this body
of evidence, including the North Carolina study, which, while finding
little clear effect of the state's .08 BAC law, did find reductions.
Consequently, DOT concluded that significant reductions have been
found in most states, that consistent evidence exists that .08 BAC
laws, at a minimum, add to the effectiveness of laws and activities
already in place, and that a persuasive body of evidence is now
available to support the Department's position on .08 BAC laws.
Overall, we believe that DOT's assessment of the effectiveness of .08
BAC laws is fairly consistent with our own. We agree with DOT on the
importance of a systems approach to combating drunk driving; we have
noted examples in this report such as the state of California, where
.08 BAC laws were not effective until other complementary measures
were put into place. DOT did not disagree with our discussion
concerning the limitations and methodological concerns for three of
the first four studies or with our assessment that recent studies
reach different conclusions about the effectiveness of .08 BAC laws;
we believe those study results must be viewed in the context of their
limitations and conclusions. Although DOT stated that studies showed
significant reductions in most states, the 11-state study
demonstrated reductions associated with .08 BAC laws in a minority of
states (5 of 11) and a minority of the measures (9 of 33) it studied.
In addition, many of the results DOT cited as consistent evidence
supporting its position were reductions that study authors determined
not to be statistically significantthus, no conclusions on the
effectiveness of .08 BAC laws can be drawn from them. Although we
characterize the strength of the study results differently, we and
DOT reach essentially the same conclusion regarding the effectiveness
of .08 BAC laws, both by themselves and in combination with other
measures.
SCOPE AND METHODOLOGY
------------------------------------------------------------ Letter :7
To determine the effect of .08 BAC laws on the number and severity of
alcohol-related crashes, we analyzed the body of research published
between 1991 and 1999. Of the seven studies, five were published by
NHTSA, one by the state of California, and one by the American
Journal of Public Health. We reviewed the studies' methodologies,
findings, and conclusions and met with study authors at NHTSA, the
Pacific Institute for Research and Evaluation, the California
Department of Motor Vehicles, and Boston University's School of
Public Health. We also discussed the studies and traffic safety
issues with NHTSA officials in Washington, D.C., Boston,
Massachusetts, and San Francisco, California; officials of the
American Automobile Association, the Insurance Institute for Highway
Safety, the National Sheriffs Association, Mothers Against Drunk
Driving, the American Beverage Institute, the National Restaurant
Association; and state traffic safety and law enforcement officials
in California.
The scope of our study was limited to the effect of .08 BAC laws on
the number and severity of alcohol-related crashes. We did not
review several other arguments raised by both proponents and
opponents of .08 BAC laws; for example, while we describe the medical
evidence on impairment, we did not evaluate that evidence. In
addition, our ability to review the severity of alcohol-related
crashes was limited by the fact that the FARS database--used entirely
by five of the seven studies and in part by a sixth--includes only
fatal crashes. The .08 BAC laws reviewed may have had a greater or
lesser effect on nonfatal crashes than it did on fatal crashes.
Finally, section 2008 of the Transportation Equity Act for the 21st
Century required us to review the effect of .02 BAC laws for drivers
under 21 in reducing the number and severity of alcohol-related
crashes. As agreed with your staff, we will not address those laws
as all 50 states and the District of Columbia now have laws
establishing BAC levels of .02 or less for drivers under 21 years of
age.
We performed our work from August 1998 through April 1999 in
accordance with generally accepted government auditing standards.
---------------------------------------------------------- Letter :7.1
We will send copies of this report to cognizant congressional
committees; the Secretary of Transportation; and the Administrator,
National Highway Traffic Safety Administration. We will make copies
available to others upon request. If you have any questions
regarding this report, please contact me at (202) 512-3650 or Ronald
Stouffer at (202) 512-4416. Key contributors are listed in appendix
II.
Sincerely yours,
Phyllis F. Scheinberg
Associate Director,
Transportation Issues
(See figure in printed edition.)Appendix I
COMMENTS FROM THE DEPARTMENT OF
TRANSPORTATION
============================================================== Letter
(See figure in printed edition.)
(See figure in printed edition.)
(See figure in printed edition.)
GAO CONTACTS AND STAFF
ACKNOWLEDGMENTS
========================================================== Appendix II
GAO CONTACTS
Phyllis F. Scheinberg, (202) 512-3650
Ronald E. Stouffer, (202) 512-4416
ACKNOWLEDGMENTS
In addition to those named above, Steve Cohen, Amy Gleason Carroll,
Sara Ann Moessbauer, Mitchell B. Karpman, and Allan Rogers made key
contributions to this report.
*** End of document. ***