Why is deterrence so important and how can it be achieved? Most impaired drivers are never stopped. Others are stopped, but police often miss signs of impairment. It has been estimated that as many as 2,000 alcohol-impaired driving trips occur for every arrest and that, even when special drinking-driving enforcement patrols are conducted, as many as 300 trips occur for each arrest. Because the police cannot catch all offenders, the success of alcohol-impaired driving laws depends on deterring potential offenders by creating the public perception that apprehension and punishment of offenders is likely. Research has shown that the likelihood of apprehension is more important in deterring offenders than is the severity of the punishment.
The key to creating this perception is enforcement. Merely putting strong laws on the books is not enough. Enforcement efforts must be sustained and well publicized and create a realistic threat of apprehension.
How do laws define alcohol-impaired driving? The first state laws prohibited driving while intoxicated or while under the influence of alcohol. In practical terms, this meant that only obviously impaired drivers - so-called drunks - were likely to be arrested and, even then, it was difficult to obtain a conviction because no objective standard existed to prove intoxication. When the relationship between BACs and impairment of skills was established, it became possible to define offenses in terms of a BAC above a defined threshold.
Every state now uses BAC results to prosecute offenders. Initially, this was done through what are known as presumptive laws that establish a presumption of impairment at or above a specified BAC (defendants could try to rebut the presumption). Now 48 states and the District of Columbia have per se laws defining the offense as driving with a BAC above a proscribed limit, rather like a speed limit. Defendants can no longer try to prove they were not impaired, although they can challenge the validity of the BAC tests.
What does blood alcohol concentration measure? Blood alcohol concentration describes the concentration of alcohol in a person's blood expressed as weight per unit of volume. For example, at 0.10 percent BAC, there is a concentration of 100 mg of alcohol per 100 ml of blood. For most legal purposes, however, a blood sample is not necessary to determine a person's BAC. It can be measured much more simply by using sophisticated breath testing instruments.
What are the BAC thresholds for per se laws in the United States? The threshold is a BAC of 0.10 percent in 35 states and the District of Columbia. It has been lowered to 0.08 percent in Alabama, California, Florida, Hawaii, Kansas, Maine, New Hampshire, New Mexico, North Carolina, Oregon, Utah, Vermont, and Virginia. Massachusetts has a presumptive law with a 0.08 percent threshold.
Drivers with BACs of 0.10 percent or more constitute a minority of all drinking drivers on weekend nights (12 percent, according to one study) but represented 86 percent of the fatally injured drinking drivers in 1995. As long as drivers with such high BACs dominate the death and injury problem, it makes sense to focus laws and enforcement efforts on this group. Public support is strongest for laws directed at this group, although a study by the Insurance Research Council suggests this may be because Americans underestimate the amount of alcohol allowed under current legal limits. When told that amount, 44 percent of those surveyed said it is too high.
How do BAC thresholds in the United States compare with those in other countries?Alcohol-impaired driving is a serious problem throughout the industrialized world. BAC thresholds range from 0.08 in Canada, and Great Britain to 0.05 in the Netherlands and most of Australia's states, and 0.02 in Sweden. Although it appears that the typical BAC threshold of 0.10 in the United States is higher than in many countries, there are national differences in forensic testing and reporting procedures. In Britain, for example, a driver must have a reported BAC above 0.08 percent to be in violation of the law, but the reported BAC is reduced somewhat from what is actually measured to account for test variability. The net result is that a BAC closer to 0.09 percent is needed in Great Britain for a violation, whereas a measured BAC of 0.10 is sufficient for arrest in the United States.
Who can be stopped for alcohol-impaired driving? Although police cannot stop and test individual drivers without cause, they can investigate any driver who, based on established criteria, appears to have been driving while impaired by alcohol. Most alcohol-impaired driving arrests are made by officers on routine patrol who discern signs of impairment after stopping a driver for an ordinary traffic violation. In some jurisdictions, specialized patrols work exclusively on alcohol-impaired driving enforcement. Plus, police can stop drivers at roadblocks known as sobriety checkpoints.
How do sobriety checkpoints work? Police can use checkpoints to stop drivers at specified locations to identify impaired drivers. All drivers, or a predetermined proportion of them, are stopped based on rules that prevent police from arbitrarily selecting drivers to stop. Checkpoints are a very visible enforcement method intended to deter potential offenders as well as to catch violators. If checkpoints are set up frequently over long enough periods and are well publicized, they can establish a convincing threat in people's minds that impaired drivers will be apprehended - a key to general deterrence.
Are sobriety checkpoints constitutional? The U.S. Supreme Court held in 1990 that properly conducted sobriety checkpoints are legal under the federal Constitution. Most state courts that have addressed the issue have upheld checkpoints, too, but some have interpreted state law to prohibit checkpoints.
Which types of enforcement are most effective? Measured in arrests per man-hour, a dedicated police patrol is the most effective method of apprehending offenders. Such patrols may also serve general deterrence if their activities are publicized and become widely known, but this usually is not the case. Meanwhile, officers who are not part of the patrols may avoid alcohol enforcement when the patrols are operating. Sobriety checkpoints have been criticized for producing fewer arrests per man-hour than dedicated patrols, but some studies show arrest rates can be increased greatly when passive alcohol sensors are used to help police detect drinking drivers. However, focussing on arrests is a misleading way to consider the value of checkpoint. The purpose of frequent checkpoints is to increase public awareness and deter potential offenders, resulting in the ideal situation where there are very few offenders left to apprehend. For example, in the Australian state of Victoria, which has had a very extensive roadside breath testing program for several years, only one in 555 drivers stopped tested positive for alcohol to the point of breaking the law in 1993. In 1978, before the roadside breath testing program, the ratio was one positive to 45 negatives.
A 1984 Institute study in two neighboring jurisdictions demonstrated how checkpoints can change public perceptions. Fairfax County, Virginia had a long history of vigorous enforcement of alcohol-impaired driving laws and used unpublicized drinking-driver patrols to achieve relatively high arrest rates. Nearby Montgomery County, Maryland had historically lower arrest rates but used well-publicized sobriety checkpoints during the study period. Surveys of licensed drivers revealed that public awareness of enforcement programs was far greater in Montgomery County than in Fairfax County and that respondents in both counties incorrectly believed the probability of arrest was higher where checkpoints were conducted.There is also evidence that these changed perceptions can lead to fewer crashes. Checkpoint programs in Florida, New Jersey, and Virginia have led to significant reductions in alcohol-related crashes. In 1988, the Institute and the city of Binghamton, New York implemented an integrated enforcement program that emphasized the publicized use of sobriety and safety belt checkpoints. During the program's first two years, the number of drivers stopped who had been drinking dropped about 40 percent. Late-night crashes decreased 21 percent and injury-producing crashes declined 16 percent while the checkpoints were in place. Results from North Carolina's 1995 statewide enforcement and publicity campaign indicate drivers with BACs at or above 0.08 percent declined from 198 per 10,000 before the program to 90 per 10,000 after the intensive three-week alcohol-impaired driving publicity and enforcement campaign.
How can passive alcohol sensors aid in enforcement? Many people can effectively mask the overt symptoms of impairment for short periods, but it is much more difficult to hide the information available from a passive alcohol sensor, which identifies alcohol in the exhaled breath near a driver's mouth. Passive alcohol sensors are not intrusive and therefore do not violate constitutional prohibitions against unreasonable search and seizure. A 1993 Institute study of sobriety checkpoints in Fairfax County, Virginia involved police using sensors, and these officers were able to detect more offenders compared with officers who did not use sensors. Police without sensors detected 55 percent of drivers whose BACs were at or above 0.10 percent. With sensors, police successfully detected 71 percent of the drivers with illegal BACs. Results of the Fairfax study parallel previous Institute evaluations.
Is license suspension an effective sanction? Laws providing for the suspension or revocation of licenses have been shown to reduce the subsequent crash involvement of drivers who are convicted of alcohol offenses. Even after the suspension, the effects of this sanction last. Although it is known that many suspended drivers continue to drive, they tend to drive less and perhaps more carefully so as to avoid apprehension. License suspension has also led to a general reduction in fatal crashes in states wherethe threat of this sanction has been made more certain through laws that provide for administrative license suspension.
Would more severe sanctions reduce the problem? Sanctions range from fines and license suspension to jail terms or community service. Historically, the potential punishment has been severe, including a mandatory jail sentence in some states, but the probability of apprehension has been low and penalties infrequently applied. In fact, there is evidence that a sanction is more likely to be applied when judges and juries consider it to be appropriate but not too severe, such as license suspension.
The world's first per se drinking-driving laws, enacted in Norway in 1936 and Sweden in 1941, were regarded as strict because imprisonment was routinely imposed on drivers apprehended with high BACs. However, a 1975 evaluation of the effects of these laws showed no significant change in the number or rate of fatal motor vehicle crashes. The notion that the sanctions were effective has thus been characterized as "the Scandinavian myth." Officials in Norway and Sweden now are transforming their drinking-driving laws to emphasize certainty of punishment over severity - an acknowledgment that the previous approach greatly burdened their criminal justice systems without curbing hard-core offenders.
What is the effect of education and other treatment programs? Research has shown that these may have a small, positive effect on the subsequent behavior of alcohol-impaired drivers, but the effect is limited to first offenders and to those identified as non-problem drinkers. There is very little evidence that treatment programs have any effect on multiple offenders or on "problem drinkers." In addition, any positive effect has been limited to subsequent convictions for alcohol-impaired driving. No effect has been shown on subsequent crashes, whether alcohol-related or not.
Which laws have been most effective in the United States? Institute researchers evaluated the effectiveness of administrative license suspension laws, per se BAC laws, and laws requiring jail or community service after a first alcohol-impaired driving offense. During the mostly late-night hours when at least half of all fatally injured drivers have BACs of 0.10 percent or more, administrative license suspension laws were estimated to reduce driver involvement in fatal crashes by about 9 percent. Laws requiring jail or community service for a first offense were estimated to reduce driver involvement in fatal crashes by about 6 percent. The effect of per se BAC laws was estimated as a 6 percent reduction in crash involvement during daytime hours when fatal crashes typically are less likely to involve alcohol.
Laws establishing a minimum age for purchasing alcohol also have proved effective in reducing nighttime fatal crashes among young drivers. An Institute study conducted in 26 states that raised their minimum legal purchase ages during 1975-84 estimated a 13 percent reduction in nighttime driver fatal crash involvement.
Have other countries done a better job controlling alcohol-impaired driving? Australia has the most successful documented programs to reduce alcohol-impaired driving. All have in common highly visible and sustained widespread, but not burdensome, enforcement. The state of Victoria maintains an aggressive program of random breath testing of drivers. More than half of all licensed drivers each year are tested in this program. The percentage of drivers and motorcyclists with BACs above 0.05 killed in crashes dropped from 50 percent in 1977 to about 25 percent in 1995, indicating the deterrent result of the random breath testing. An Australian university study concluded the key to the random breath testing program's success is high visibility, rigorous enforcement sustained on a long term basis, and good publicity.
Why don't we test all drivers and arrest those who don't pass a chemical test? Random, widespread breath testing programs, such as those in use in Australia, would not be permitted under the Fourth Amendment to the United States Constitution. However, measures like sobriety checkpoints and the use of passive alcohol sensors are available in the United States and may prove as effective in substantially reducing not only alcohol-impaired driving but also crash deaths and injuries. The key is exposing sufficient numbers of motorists to the enforcement efforts.