Punishments for drivers whose blood alcohol content measures above legal thresholds for impairment have reduced the likelihood of repeat offenses, says University of Oregon economist Benjamin Hansen.

Hansen studied data from 1999 to 2011 in neighboring Washington, where a blood alcohol content over 0.08 is considered to be driving under the influence, the same as other states for noncommercial drivers age 21 or over. Punishments of drivers cited at that level saw a 17 percent reduction in reoffenses. An additional 9 percent reduction occurred in cases where blood alcohol contents exceeded the aggravated intoxication threshold of 0.15.

Blood alcohol content, or BAC, is the concentration of alcohol within a person's blood stream. It refers to how much alcohol is present in 100 milliliters of blood.

The findings by Hansen, who studies policy implications of risky behaviors such as marijuana and alcohol use, are in the April issue of American Economic Review, one of nation's most respected scholarly economics journals.

While the study provides some support to efforts by the National Transportation Safety Board to lower the minimum BAC threshold to 0.05, it actually makes a stronger case for instituting increasing punishments for higher blood-alcohol levels, said Hansen, who in addition to his role at the UO is a faculty research fellow of the National Bureau of Economic Research.

"If you look at fatalities involving BAC between .05 and .08 there are about 800 a year," he said. "The NTSB has to be assuming that everyone who is now drunk driving at those levels is going to stop drinking and driving when the limit is lowered to .05."

In reality, he said, most fatal accidents involved drivers with BACs ranging from 0.13 to 0.24. In Washington, he said, the average drunk driver involved in a fatality had BACs at least double the legal limit.

"These drivers are the most costly. In terms of fatality risk, a person with a BAC of .15 is about 20-30 times more dangerous than a person who is sober," Hansen said. "I think we might see even greater benefits if we were to increase the sanctions, or punishments, more steeply along the BAC distribution."

An additional step, he said, would be to lower the threshold for aggravated BAC to 0.12. Such steps, he wrote in the study, might make drivers "internalize the external costs of drunk driving."

— Jim Barlow, Public Affairs Communications