The idea of using a designated driver for a group night of hearty partying is pretty standard, but a new report in the July issue of The Journal of Studies on Alcohol and Drugs casts a shadow of doubt on some of those drivers.

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Researchers talked to and breathalyzed a 1,100 people exiting Florida bars, and found almost four in 10 designated drivers had been drinking. Twenty percent of them were considered impaired.

"This study is alarming on many, many levels," said Tracy Noble, a spokeswoman for AAA Mid-Atlantic. Noble said the designated driver has a responsibility to stay sober.

But it's also up to the group to pick a responsible designated driver.

Gary Poedubicky, Acting Director of the New Jersey Division of Highway Traffic Safety, said designated drivers should be someone who knows the roadways, and has experience driving.

"In some cases, the designated driver is chosen based on who in the group is least intoxicated and that's not proper concept of the designated driver program," said Poedubicky.