Jeff Rossen of NBC's TODAY Show recently conducted a social experiment that yields some surprising results: Holiday party drinking may make us drunker than we think, which can impair our judgment when deciding whether to get behind the wheel of a vehicle.

A lot of us think we know our limits: "I can have a couple of drinks. If I'm not slurring my words or stumbling, I'm OK."

But, authorities say, too often people don't know their own limits. According to government data, during Christmas and New Year's, 40 percent of all traffic deaths involve alcohol. In just the few days surrounding those two holidays, an average of 304 people die in drunk-driving crashes, says the U.S. Department of Transportation.

"The misperception is that people feel they can go out and have a few drinks, when in reality, one drink can impair you," said Michael Halfacre, director of New Jersey Division of Alcohol Beverage Control.

To demonstrate the dangers, TODAY's experiment invited a group of friends to a restaurant telling them it was for a story about holiday drinking. What they didn't know was that after the party, a local police officer working with TODAY would be giving them Breathalyzer and field sobriety tests.

Half the guests were told to drink as they normally would, and the other half were told not to drink at all, so they could serve as designated drivers. (Car services were also hired as a backup to make sure everyone got home safely.)

One partygoer who drank, Kim, thought she would be OK if she waited "at least an hour, hour and a half" before she drove. But when she was given an Breathalyzer test after that time, she was surprised to find that after only two drinks, she had a blood alcohol level of 0.1 percent (the legal limit is 0.08 percent).

"I thought I could have two and be safe," Kim said. Authorities say that's a common mistake. Even after you stop drinking, your blood alcohol level can continue to rise as the liquor seeps into your system.

Another partygoer, Ron, thought he could safely drive two blocks home. But given a field sobriety test, he was unable to do it. His blood alcohol level was 0.13.

"I probably would have gotten into a car to drive home had I been at a local bar," Ron admitted. "God forbid I'd hurt someone or killed somebody."

Please --Before you go out tonight-- Watch this video:
NBC's 'social drinking experiment'

Recognize the undisputable facts. Always have a designated driver. If you're drinking, don't drive. Have a Happy New Year!!