One of those is Michigan, where the new restrictions go into effect in March. Michigan's new law makes it one of several states -- including Connecticut, Illinois and New York -- that have introduced restrictions in the last three years, joining other states that have similar laws in place already. There has been much grousing by teenagers in Michigan in anticipation of the new law going into effect.
Under the new Michigan law, new teen drivers will not be allowed to have more than one non-family passenger aged 20 or younger in their vehicle, unless accompanied by a parent, guardian or another adult aged 21 or over who's been approved by a parent. The law makes exceptions for traveling to school or school-sanctioned events. Teens also won't be allowed to drive between 10 p.m. and 5 a.m. unless they are driving to or from work; the previous law had allowed teens to drive until midnight.
Laws passed in other states have similar restrictions, although the exact times and number of teen passengers varies from state to state. The laws are part of a "graduated licensing" approach that is in place in many states, where teens gain more driving privileges as they get older and accrue more experience.
"Based on the studies that have been done after the laws have been strengthened with these restrictions, we found that strong nighttime-driving and teen passenger restrictions have led to much lower crash rates, and fewer crash fatalities, for teen drivers," said Anne McCartt, senior vice president for research for the Insurance Institute for Highway Safety (IIHS).
In Connecticut, for example, the number of teens involved in fatal crashes dropped by a whopping 62 percent in 2009, after the state imposed tougher laws and restrictions, according to a state study. In Illinois, the number of teen-driving deaths dropped to 71 in 2009, down from 146 in 2007, after a law adding these kinds of restrictions was passed, according to Illinois State Police figures.
"And the stronger the law, the greater the effect," said McCartt.
The reason for restricting the number of teenaged passengers in the vehicle is because "having more than one teenaged passenger just adds another distraction for the driver," said Barbara Harsha, executive director of the Governors Highway Safety Association (GHSA). "The research shows that the risk doubles with the addition of each teenage passenger."
McCartt noted, "Having more teenaged passengers in the car is also related to risk-taking. It can contribute to more of a party atmosphere, with teens perhaps drinking, eating, not using their seatbelts, playing loud music -- all of which are going to be a distraction and make the driver less likely to be focused on the task of driving."
Teen passengers riding with beginners can also increase the risk of a crash by creating peer pressure for the driver to take more risks behind the wheel, she added.
The GHSA is a public interest group that advocates to Congress and the White House on behalf of state highway safety agencies, and strongly supports teen driving restrictions.
"We've absolutely seen a steep decline in teen driving fatalities due to these laws," said Harsha. "These laws have been well-researched and found to be extremely effective. And in those states that don't have such restrictions, we are encouraging states to strengthen the laws by implementing these restrictions."
Harsha says the nighttime driving restrictions are important because "that's when there is the greatest exposure to risk. It's harder to see, and harder to make judgments, and other high risk drivers are on the road, like drunk drivers."
Teens make up the vast majority of beginning drivers and their crash rates are much higher than those of adults. According to the IIHS, 16-yar-olds have higher crash rates than any other age group, including older teenagers.
"Teen drivers have the combination of being a lot less experienced when it comes to driving, and being and a lot less mature" – the latter of which leads to "a higher propensity for risk-taking," said McCartt. "Young drivers tend to overestimate their own driving abilities while, at the same time, underestimating the dangers of the road."
Here are more details on the teen licensing laws and restrictions in each state can be found here.