We all know teenagers act differently when they're with their teenage friends.

So why should we expect things to be any different when they're driving a car? As a parent you don't— and that's part of why you worry about your teen driver.

Just one teenage passenger increases risky driving behavior by two and a half times.

With 2 or more teenage passengers, risky behavior increases 3 times .

It really depends on the teenage passenger. A more cautious friend, means your teen will most likely drive safer.

Put the neighborhood bad boy in the car, the risk increases.

There's one passenger who decreases unsafe driving behavior when they ride along with a teen driver.

You guessed it— Parents!

High school drivers with male passengers drove on average about 5 mph faster than when they had a female passenger

How about riding with their siblings? There's still an increased risk.

“I don’t think it really matters about five [mph] over, I think most people do five over anyway, that would be really annoying if it beeped just for going five over because there are some places where its really annoying to go the actual speed limit.”

“[I] definitely [drive differently]… [I] go probably about what the speed limit says when my parents are in the car, the radio is normally off, two hands on the wheel, always looking around but when I’m on my own I’ve got the radio on just relaxing.”

“If someone’s speeding out of control... its bad.... As long as you’re in control it should be fine and slower people should move to the right.”