(Harrisburg) -- The commonwealth's new teen driver law goes into effect Tuesday, December 27. State Representative Kathy Watson, a Republican from Bucks County, says she worked for six years on the new law designed to improve safety for teen drivers. She says one of the key parts of the new law is a prohibition on drivers with so-called "junior" licenses from carrying more than one passenger under age 18 who is not an immediate family member. Watson says the measure is in effect for the first six months that junior drivers are licensed. "They still say, scientifically, when they've done the studies, that the greatest distraction for a teen driver isn't the cell phone or texting or makeup or whatever. It is other teens," Watson says. She says the law also makes seatbelt use a primary offense for junior drivers and passengers under age 18, and it requires an additional 15 hours of supervised training including night and poor weather driving. She says the law will be reviewed in two years to see if changes need to be made.