Picking a designated driver for a night on the town with friends sounds like a great idea, but a new U.S. study suggests designated drivers often don’t take their job seriously and go ahead and drink anyway -- sometimes close to the point of intoxication.

A team of U.S. researchers say their study suggests campaigns that encourage the use of designated drivers aren’t doing much to control drunk-driving and may need to be re-thought.

The study looked at patrons leaving bar in a nightclub district in Gainesville, Fla.,. Over six nights, the researchers stopped 1,071 people – mostly males in their 20s -- leaving bars who agreed to take alcohol breath tests, including 165 who said they were the designated drivers. The average age of the bar patrons was 28.

The researchers found about 40 per cent of the designated drivers admitted they had not abstained from drinking all night and had a couple of drinks. Their breath tests showed that 17 per cent of the drivers had blood alcohol levels between .02 and .05 per cent, while 18 per cent were at .05 per cent or higher.

The researchers say that alcohol begins to dull a person’s driving skills at a blood level of .02 per cent. By .05 per cent, the ability to drive safely is clearly impaired. That’s also the allowable blood alcohol limit for drivers in a number of European countries, such as Germany, France and Italy.

The U.S. limit is .08 per cent, but just last month, the National Transportation Safety Board recommended lowering the legal limit to .05. Canada’s limit is also .08 per cent.

The researchers found it interesting that so many so-called designated drivers were choosing to drink, knowing they would have to drive later that night.

They’re drinking at a rate in which psychomotor functions are impaired and their ability to operate a motor vehicle is significantly inhibited,” lead researcher Adam Barry, an assistant professor of health education and behaviour at the University of Florida told CTV News.

Barry suspects some of the drivers thought that as long as they didn’t feel drunk, they were all right to drive.

"People do try to use that as a measuring stick," he said in a statement. "But alcohol is insidious."

He says someone on the brink of drunkenness driving a group of drunken, sometimes rowdy, passengers, at night -- when their vision in already compromised -- is flirting with disaster.

"If you're going to be a designated driver, you should abstain from alcohol use completely."

The researchers add while designated-driver campaigns are popular, their study, along with previous research on the subject, suggests the concept is not working.

"Should the current status quo continue, it is likely that the scientific literature will continue to indicate that (designated driver) campaigns fail to effectively prevent impaired driving," they write.

The results from the study aren’t surprising, according to one Calgary police traffic inspector.

"(Designated drivers) start the evening with good intentions…but that could evolve into their partaking of alcoholic beverages," Insp. Dean Lagrange said, adding that the results from the U.S. study most likely reflect how so-called designated drivers in Canada behave.

The study results appear in the July issue of the Journal of Studies on Alcohol and Drugs.