By David Brown
Washington Post Staff Writer
Monday, April 13, 1998; Page A01

The number of lives that might be saved if a uniformly more stringent definition of "driving while intoxicated" were adopted would be relatively small, perhaps as few as 500 each year. It would constitute a tiny reduction in the annual death toll on the nation's roads. However, the people who could be labeled "drunken drivers" under a stricter standard of legal intoxication are far from a sober lot.

Their bloodstreams carry enough alcohol to measurably impair the symphony of neurological responses required to drive a car well. If these people are not staggering drunk -- and, as a group, they aren't -- they nevertheless stand at a critical threshold of inebriation. Any more liquor, and their chances of killing someone on the road begin to rise steeply.

Those are some of the conclusions of 30 years of research on drinking and driving Congress will consider before the end of the month, when the House and Senate will have to decide whether to throw the federal government's weight behind the movement for a stricter definition of "driving while intoxicated."

The bill in question would deny a state as much as 10 percent of its federal highway funds if it fails to set the "per se threshold" for intoxication at 0.08 grams of alcohol per deciliter of blood. At such a threshold, a person can be convicted of driving while intoxicated on the basis of the test alone. Authorities don't have to show evidence of dangerous or erratic driving.

Fifteen states have a standard of 0.08, while the rest use 0.10. The District is considering implementing a 0.08 threshold.

The liquor, bar and restaurant industries oppose the legislation, arguing it would severely damage their businesses without appreciably improving highway safety. Many law enforcement and public health groups support the bill, in part because they believe its benefits are proved and, in some ways, obvious: Saving 500 lives is better than not saving 500 lives.

There is little dispute among any of the parties that alcohol is a key element in highway deaths. In 1996, for example, there were 41,907 road fatalities of all types -- drivers, passengers, pedestrians, bicyclists. Of those, 41 percent involved alcohol in some way.

Virtually every study has shown that most of the drinking and driving problem is caused by the very drunk, not the slightly drunk.

For example, statisticians at the Insurance Institute for Highway Safety -- a research firm in Arlington financed by insurance companies -- several years ago categorized driver fatalities in 1991 by blood alcohol level. Forty-eight percent of fatally injured drivers had measurable alcohol in their blood, and most of those people had very large amounts.

Specifically, 40 percent of the dead drivers had blood alcohol greater than 0.10, and half that group came in above 0.20, a physiological state in which severe confusion and lack of coordination is universal. Only 8 percent of the dead drivers had blood alcohol below 0.10 (but still detectable). Those who fell in the 0.08-to-0.10 range made up only 2 percent of the fatalities.

More recently, the National Highway Traffic Safety Administration (NHTSA) examined the blood alcohol levels of all 24,762 drivers tested for alcohol after fatal crashes in 1996. Sixty percent had no measurable alcohol, and about 31 percent had readings above 0.10. Only 2.4 percent had readings between 0.08 and 0.10.

Together, these statistics suggest that drivers whose blood alcohol would be made illegal under a 0.08 standard account for very little of the drunken driving problem, at least as defined by fatality. (There are no reliable statistics on intoxicated drivers' contribution to accidents in which no one dies.) Lowering the threshold won't get at the heart of the problem, which is the presence of far drunker people on the road.

Nevertheless, there's some evidence that a 0.08 definition of legal intoxication has a general deterrent effect.

NHTSA compared the average percentage of "alcohol-related" fatalities in states having a 0.08 threshold with that in 0.10 states. The stricter standard made it slightly less likely that a fatality would be alcohol-related. Specifically, 39 percent of the fatalities in the 0.08 states involved alcohol, compared with 42 percent in the 0.10 states.

Similarly, a team of biostatisticians at Boston University reported in the American Journal of Public Health two years ago that states moving to the 0.08 standard, as a group, experienced a drop of about 16 percent in the proportion of fatal crashes involving drivers with blood alcohol greater than 0.08. Curiously, they found a similar reduction in drivers with blood alcohol that surpassed 0.15 -- namely, in people who were far above the new and stricter limit.

"There seems to be a deterrent effect across the whole range of BACs [blood alcohol concentrations], including the very high ones," said Allan F. Williams, a researcher at the Insurance Institute for Highway Safety, who did not participate in this study. "It's a little mystifying to me, but also encouraging."

The estimate of the number of lives that might be saved if 0.08 were universally adopted ranges from 500 to 1,000 a year.

Although the benefits of a lower intoxication standard are modest, there is little question that people with 0.08 grams of alcohol per deciliter of blood under their belts are less competent drivers.

Studies conducted over the last 30 years have shown conclusively that alcohol has a "graduated" effect on human neurological response. Impairment is detectable -- at least under laboratory conditions -- at levels far below those of legal intoxication. Impairment becomes more severe as blood alcohol rises into the clearly intoxicated range.

"There is no question that nearly everything you can think of in terms of driving impairment is evident by .08," said Herbert Moskowitz, president of the Southern California Research Institute and a faculty member of the University of California at Los Angeles.

At 0.08, he said, many drivers do not think they are impaired and may not appear to be impaired. Nevertheless, under simulated driving conditions, they have clear deficiencies in their abilities to divide their attention between various visual stimuli, and to process new information quickly.

"Those [two skills] in many ways are the essence of driving," said Moskowitz, a longtime researcher on the behavioral effects of alcohol who has reviewed the scientific literature on the subject.

The number of drinks required to raise blood alcohol to 0.08 varies greatly depending on body size, metabolism and sex. Generally speaking, a 137-pound woman who consumes three drinks in one hour, or a 170-pound man who consumes five drinks in two hours, reaches that level. An individual's ability to perform complex tasks, such as driving, at a given blood level also varies greatly from person to person, depending on age and experience of being intoxicated under demanding conditions.

Is alcohol-related impairment, even at low levels, of importance on the road? Or is it something that has little meaning, even though it can be measured in the lab?

Statistician Paul L. Zador tried to get at that question in a study published in the Journal of Studies on Alcohol in 1989.

He looked at how the risk of having a fatal accident changed as a function of blood alcohol. He used only single-vehicle crashes with driver fatalities because they are the accidents in which there is presumably the alcohol and death link.

Drivers with readings between 0.02 and 0.04 had 1.4 times the risk of dying, compared with people who had no alcohol in their blood. For people between 0.05 and 0.09, the risk was 11 times higher. For those 0.10 to 0.14, the risk was 48-fold, and for those above 0.15, 380-fold.

Zador also looked at how the risk of death, in any given blood alcohol range, differed depending on a driver's age or sex.

He found that the younger a driver, the greater the risk, with intoxicated young women at the greatest risk. For example, women 21 to 24 years old with blood alcohol in the 0.05 to 0.09 range had 35 times the risk of being killed as similar women who hadn't been drinking.

So how many people are there out on the road with alcohol on board?

Alcohol researchers have attempted to answer that question with something called the National Roadside Survey, which has been conducted three times in the last quarter century -- in 1973, 1986 and 1996.

In the latest study, drivers were randomly stopped (at randomly selected sites) on a Friday or Saturday night and asked to voluntarily take an alcohol breath test. Ninety-six percent agreed to. Those registering blood alcohol above 0.05 were assisted in finding a ride home, but none was arrested.

In 1996, the researchers found that 83 percent of drivers had negligible or no alcohol in their blood. About 9 percent of drivers fell in the 0.005 to 0.049 range. Five percent of drivers were in the 0.05 to 0.099 range. Registering above 0.10 were 3 percent of drivers.

The fraction of drivers in every category was lower in the 1996 survey than in the two earlier ones, although the greatest decline was in the low blood-alcohol category. For example, the percentage of drivers in the 0.005 to 0.049 range was 22 percent in 1973 and 18 percent in 1986, but by 1996 was only half that.