A message from the state of California to its 16- and 17-year-olds: Dnt txt n drv — thx.

A law signed by Gov. Arnold Schwarzenegger on Thursday will require those teens to put down all cell phones and other electronic devices while driving. Older drivers will be able to use hands-free devices but minors won't enjoy that luxury — in part because of the popularity of text-messaging among teens.

"The simple fact is that teenage drivers are more easily distracted. They are young, inexperienced and have a slower reaction time," Schwarzenegger said in a statement after he signed the legislation into law. "We want to eliminate any extra distractions so they can focus on paying attention to the road and being good drivers."

The law barring cell phone use by drivers under 18 will take effect July 1, as will the law restricting cell phone use among older drivers, which the governor signed last year.

Violators will be fined $20 for the first offense and $50 for subsequent offenses. Both laws include exceptions for drivers who need to make emergency calls.

Schwarzenegger's signature means California joins 15 states and the District of Columbia in banning the use of wireless communication devices for teenage drivers. Nearly a dozen other states are considering similar action, according to the American Automobile Association.

The governor cited statistics by the California Highway Patrol that cell phone use is a primary cause of accidents caused by distracted drivers. He also referred to a Ford Motor Co. study saying teens are four times more likely to be distracted than adults by cell phone use.

A 2001 report by the National Highway Traffic Safety Administration found that 16-year-old drivers have a crash rate three times higher than that of 17-year-olds, five times greater than 18-year-olds and almost 10 times greater than drivers ages 30-59.