Alcohol as a Cause of Traffic Crashes

Alcohol-related traffic crashes are not necessarily caused by alcohol. Many are, but no one knows the exact proportion.

There is overwhelming evidence that

  1. alcohol adversely affects driving-related skills such as vision, reaction time, judgment, and the ability to divide attention, and
  2. intoxication decreases driving performance.

It is also clear that drinking drivers who crash are similar in many ways to sober drivers who crash. Both groups are disproportionately young, male, single, suffer from alcohol or drug problems, and are characterized by aggression, hostility or other “undesirable” attitudes and personality traits.

Drunk drivers don’t become model drivers when sober. Even when completely sober, those who sometimes drive drunk are at high risk of being involved in traffic accidents. But there’s every reason to believe that alcohol frequently contributes to crashes.

One technique that demonstrates this is called responsibility analysis. By examining multiple-vehicle crash reports without knowledge of drivers’ blood alcohol concentrations (BACs), researchers estimate the degree to which each driver was responsible for his or her crash. In a sample of injured drivers in Monroe County, NY, it was estimated that 34-43% of sober drivers were responsible compared to 74-90% of intoxicated drivers (BAC of 0.10 or higher). 1

A large study of 1,882 fatally injured drivers in several states concluded that 68% of sober drivers and 94% of intoxicated drivers (0.10 BAC or higher) were responsible for their crashes. The responsibility rates were higher in this study, which included single vehicle crashes, largely because drivers in single vehicle crashes are almost always deemed responsible. Nevertheless, the pattern is the same: responsibility for accidents increases with intoxication. 2

How many drunk drivers would have had accidents if they were sober? Again, no one knows. But one expert, James Hedlund, has identified three broad types of drinking drivers, for whom the answer probably differs:

  1. “normal” drivers who are social drinkers. Such drivers may miscalculate the effects of alcohol on their performance. Dr. Hedlund asserts that alcohol increases their crash risk and their crash rates would decrease substantially if they did not drive after drinking,
  2. “high-risk” drivers. These are frequent drinkers, for whom alcohol abuse “may be just another manifestation of risk-taking behavior or may enable this behavior by removing what inhibitions they have.” Abstaining may not reduce their crash rates much, and
  3. alcoholics, for whom alcohol abuse is an integral part of life. Abstaining would require a complete lifestyle change. If they abstained, their crash rates should drop significantly. 3

Dr. Hedlund observes that

The three groups are affected differently by measures to limit drinking and driving. “Normal” drivers can be deterred by the legal consequences of arrest and sanction for impaired driving and also can be affected by education and prevention methods. Arguably, much of the reduction in alcohol-involved crashes may have come from changes in the behavior of this group. In contrast, alcoholics are unlikely to be affected by anything that does not deal directly with their alcoholism. Traffic safety can play an important role by screening DWI offenders for alcohol problems and assuring that they are referred to treatment as appropriate, but other traffic safety measures are unlikely to have much effect. “High-risk” drivers are perhaps the hardest group to affect. Deterrence, even arrest and punishment, may have little influence on their behavior. Some high-risk behavior is outgrown as drivers mature. However, since high-risk behavior is rooted so deeply in some drivers’ personalities, any change requires measures for broader than those available to traffic safety. 4

Although it appears to be significant, the proportion of alcohol-involved traffic accidents that would have occurred even if the drivers had been sober remains unknown.


  • 1. Terhune, K.W. and Fell, J.C. The Role of Alcohol, Marijuana, and Other Drugs in the Accidents of Injured Drivers. Washington, DC: National Highway Traffic Safety Administration, 1982 (DOT HS 806 181).
  • 2. Terhune, K.W. et al. The Incidence and Role of Drugs in Fatally Injured Drivers. Washington, DC: National Highway Traffic Safety Administration, 1992.
  • 3. Hedlund, J.H. “If they didn’t drink, would they crash anyway?” -- The role of alcohol in traffic crashes. Alcohol, Drugs and Driving, 1994, 110(2), 115-125.
  • 4. Hedlund, J.H. “If they didn’t drink, would they crash anyway?” -- The role of alcohol in traffic crashes. Alcohol, Drugs and Driving, 1994, 110(2), 115-125.

filed under: Drinking and Driving