a particularly lethal combination. >> when there are other teens in the car with the teen driver, a vehicle can become a party on wheels. that is a recipe for disaster. >> reporter: a 15-year-old girl was killed in an accident in michigan. three other friends were in the car and the driver was 19 years old. with each additional passenger in a car driven by a teenager, the risk of fatality soars. young drivers are the most likely to speed. to make judgment errors. to be distracted. and to text while driving. in one study researchers placed cameras in cars with 16-year-olds behind the wheel. >> oh, my god! >> ah! >> reporter: they revealed a shocking number of driver errors even though they knew they were being filmed. >> sorry! >> reporter: the new transportation bill signed into law a few days ago by president obama tries to deal with the problem of teenage drivers by encouraging states to put restrictions on young drivers. such as not allowing them to drive at night or with passengers in their cars until they have gained some experience behind the wheel. if enough states go along with