According to some recent research, it appears that they do. As reported by CBS News, as speed limits have increased in recent years, more fatal car accidents have occurred. It is only logical to assume that the faster you are traveling when you get into an accident, the more severe the crash will be.
Parents of teen drivers in Georgia would be wise to prohibit their children from driving with passengers in their car. According to USA Today, a study of 16 to 17-year old drivers found that not only did the presence of passengers in the teens' cars increase the risk of being in an accident, the risk actually increased further proportional to the number of passengers in the car.