"Our study correlated urgency, a specific type of impulsivity, to drinking and driving," McCarthy said. "Individuals with a high degree of urgency tend to act impulsively when they are in both positive and negative emotional states. By looking at personality traits that correlate with drinking and driving, we can help people understand how their personalities might incline them to choose the risk of driving after drinking. Once a person knows this, they can decide to take extra care to moderate their drinking or be prepared to call a cab, hop on a bus or ask a designated driver for help."

In one study, McCarthy and his colleagues evaluated 29 individuals based on whether they had recently driven after consuming three or more drinks in the previous two hours. The study participants were repeatedly presented with the option of receiving a small amount of money (five cents) as a reward after waiting five seconds or a larger amount (15 cents) as a reward after 15 seconds. Choosing the shorter wait and smaller reward was considered an expression of impulsive behavior.

Participants completed the test twice -- once while sober and once after drinking alcohol. Individuals who reported drinking and driving were not different from other participants in their impulsivity when sober. After consuming alcohol, those who reported drinking and driving exhibited a significantly higher degree of impulsivity.

In the second study, McCarthy and his colleagues surveyed more than 800 individuals about their drinking and driving beliefs and behaviors. The survey also assessed the degree to which they expressed impulsive characteristics such as urgency, lack of planning or perseverance, and sensation seeking. Urgency was found to be the characteristic most associated with drinking and driving.

"Our studies of urgency help explain why people end up with DWIs even though, while sober, they abhor the notion of drinking and driving," said McCarthy. "Under the influence of alcohol, some people may feel an exited emotional state and hence greater urges to act on an impulse that they would normally not condone."

McCarthy noted that alternatives to drinking and driving can take more time than some intoxicated individuals are willing to wait. Impulsive personalities, enhanced by alcohol, tend to take the short term reward of convenience and discount the risk of death or legal action. He suggests reducing wait times for taxis, public transit or other transport options could give the impatient drinker a quick and safe option to get home. City planners and policy makers could help by providing bus routes and taxi stands near drinking establishments.

The study, "Direct and Indirect Effects of Impulsivity Traits on Drinking and Driving in Young Adults," was published in the Journal of Studies on Alcohol and Drugs. The study, "Acute alcohol effects on impulsivity: associations with drinking and driving behavior," was published in the journal Addiction.

At the University of Missouri, officials strive to end drunk driving with several programs. "Stripes" is a free taxi service coordinated by MU that provides approximately 10,000 rides per year. MU officials also have worked with the city of Columbia to increase the availability of transportation by providing taxi stands near drinking establishments frequented by students. Another program, "Cheers," provides free soda to designated drivers at most Columbia bars.