An illegal per se law makes it an offense in and of itself to drive with a blood alcohol concentration (BAC) measured at or above the established legal level, whether or not the driver or operator exhibits visible signs of intoxication. Lowering the BAC limit to .08 sets the legal limit to a point at which driving skills are proven to be compromised. At .08 BAC, all drivers, even those who are experienced drinkers, show impairment in driving ability. For the great majority, there is serious deterioration in driving performance at .08 BAC.

Measuring Impairment

The amount of alcohol in a person’s body is measured by the weight of the alcohol in a certain volume of blood. This is the blood alcohol concentration or BAC. The measurement is based on grams per deciliter (g/dl), and in most states, a person is considered legally intoxicated if his or her BAC is .10 g/dl (.10 percent) or greater; that is, alcohol makes up one-tenth of 1 percent of the person’s blood.

With each drink consumed, a person’s BAC increases. Although outward appearances vary, virtually all drivers and motorcycle operators are substantially impaired at .08 BAC. Laboratory and on-road research show that the vast majority of drivers, even those who are experienced drinkers, are significantly impaired at .08 with regard to critical driving tasks such as braking, steering, changing lanes, divided attention tasks, and judgement. The risk of being in a crash rises gradually with each BAC level but then rises very rapidly after a driver reaches or exceeds .08 BAC, compared to drivers with no alcohol in their system.

While there is no “safe” amount of alcohol for drivers, most people can drink moderately and drive legally when the illegal per se limit is set at .08 BAC. A 170-pound male typically would have to consume more than four drinks (e.g., 12 oz. cans of beer) in one hour on an empty stomach to reach a BAC of .08. A 135-pound female typically would have to consume three drinks in the same time frame.

.08 Laws Work

The National Highway Traffic Safety Administration (NHTSA) examined the effects of lowering the legal BAC limit from .10 to .08 and implementing an administrative per se law in California. The 2 new laws and the associated publicity reduced the number of expected alcohol-related fatalities by 12 percent in 1990.

Another study on the effects of lowering BAC levels to .08 compared the first 5 states to lower their BAC limit to .08 (California, Maine, Oregon, Utah, and Vermont) with 5 nearby states that retained the .10 limit. Overall, the .08 states experienced a 16 percent reduction in the proportion of fatal crashes with a fatally injured driver whose BAC was .08 or higher and an 18 percent reduction in such crashes with a fatally injured driver whose BAC was .15 or higher.

State Laws

As of April 1998, 48 states had a per se law (except Massachusetts and South Carolina). In 32 of those states and the District of Columbia, the legal limit is .10 BAC per se. Fifteen other states have .08 as the legal limit.

.08 BAC Law Deters Impaired Driving

Lowering the limit to .08 sends a message that the state is being tougher on impaired driving and makes people think twice about driving after they have had too much to drink. According to recent research, if every state adopted a .08 BAC per se law, hundreds of lives would be saved every year, with thousands of injuries prevented and millions of dollars saved.

For more information on .08 per se laws, see NHTSA’s Setting Limits, Saving Lives—The Case for .08 BAC Laws, DOT HS 808524, December 1997. Also, visit the NHTSA Web site (www.nhtsa.dot.gov).