Maine’s lawmakers had the best of intentions two years ago when they forbid 16- and 17-year-olds from using cell phones while driving.

They probably realized three things even then:

First, that the law was practically impossible to enforce. Unless police happen to know the young driver, they are unable to tell a 17-year-old from an 18-year-old behind the wheel of a car.

Second, peer pressure – in this case to be constantly connected and in touch – is an almost overwhelming force for teens. Too many can’t seem to go 10 minutes without talking on their phone or sending a text message. It’s just part of the culture.

Finally, sensible advice too often tends to go in one teenage ear and out the other. Legislators may say “no cell phones,” but that doesn’t mean teens will obey.

In effect, Maine’s law was unlikely from the start to have much impact.

Now comes proof. The Insurance Institute for Highway Safety recently issued a report calling into question the effectiveness of laws restricting teenage cell phone use.

Researchers watched students leaving high schools in North Carolina, which has a law, and in South Carolina, which does not.

The rate of cell phone use by 16- and 17-year-olds was about the same in both states. Basically, the study found that North Carolina teens were ignoring the state’s law forbidding their cell phone use. Worse, cell phone use actually went up slightly after the law was enacted.

The National Transportation Safety Board in 2003 first recommended that states limit or bar young drivers from using cell phones. The reasons were obvious: teen drivers have high accident and death rates. A variety of studies had shown that they are easily distracted from the complex task of driving, too often with tragic consequences.

Since then, 17 states, including Maine, have adopted cell phone restrictions in licensing requirements for teen drivers.

Such laws, in a way, may be more effective with parents than with teens. And, since parents usually own the cars operated by teenagers, they may be more effective than legislators and police officers at encouraging, and even enforcing, use.

Parents should constantly reinforce the law, reminding their teens that using a cell phone while driving is not only illegal but dangerous. Parents must also set a good example themselves, perhaps making a visible demonstration of turning off their cell phones while driving, particularly when children are in the car.

Kids learn safe driving habits from their parents, and they start at a young age. If they spend 15 years in a car watching mom yaking on her cell phone, guess what they are going to do when their turn 16?

Parents should look at car travel as a precious opportunity to talk to their children, not on their cell phones.

Finally, parents usually control the car keys. They should clearly warn their teens that if they see them driving while talking on a cell phone, they will have a choice: give up the car or give up the cell phone.