[Before I get into this subject, I want to nod to Chapter 20 of David Friedman's _Hidden Order_, from which this explanation is derived. This was inspired by a report by the Institute for Highway Safety on the NY hand-held phone ban.]
After initial reports that the hand-held phone ban in New York State was working, compliance with the law has dropped off. The report says that's to be expected, simply because motorists don't comply with new laws very well. There's another reason, though: the law is stupid.
Driving is a highly skilled activity. It takes about forty hours of on-the-road training before a driver is considered competent to drive without an experienced driver in the car. Driving is also a fairly dangerous activity. Forty thousand people a year die on American roads. Walking, flying, and riding are all dangerous, too. What makes driving so different is that very often a poor driver kills rather than merely dying. Even if you're careful around roads, you can still get hit by a careless driver.
People want to be at least reasonably safe near roads. Besides required licensure of drivers, automobiles must have yearly safety inspections. These inspections are not designed to keep the driver safe, but instead to keep the public safe. You can see this because they check the lights and the brakes. The lights on a car are mostly there to signal to other people the intended path of a car. The brakes are there not only to stop the driver from getting hurt, but to stop the car from hurting someone else.
There are other constraints on drivers. Besides being licensed, they must be old enough to be responsible behind the wheel. Age is not the only determinant of responsibility. An irresponsible driver can be distracted from his driving. Driving is a skilled activity that requires concentration. If that concentration is broken, the driver can cause a crash. Many accident stories start with "I was doing X..." where X was not a normal part of driving. For example, today's newspaper had a report of a truck driver who had an accident because he was changing his clothes.
People, to be safe from distracted drivers, want laws which discourage distraction. Herein lies the problem with the hand-held phone ban. It bans one particular type of distraction, when the problem is not any one type of distraction, but any type of distraction. A state legislature could try to micro-manage driver's distractions, eliminating them one by one, but in the end, they will fail. People are inherently distractable, but each person is distractable in different amounts by different things.
There is no reasonable set of laws regulating external behavior which will prevent all drivers from being distracted. Each driver has a different set of external behavior which distracts or doesn't distract them. Perhaps they are very good at balancing a laptop on one leg, a mouse on the other, and reading their email while they drive? Perhaps someone else can't chew gum and drive at the same time? What is needed is a law that says "Thou shalt not be a distracted driver."
In essence, the way that accident liability is structured does that. In New York State, the last person who could have stopped the accident is at fault for not having done so. If you have an accident, and you were distracted, you have to pay for it. It all goes through your mandatory automobile insurance, but you can be sure that in the long run, you will pay out of pocket for being distracted.
That is why the hand-held cell phone ban is stupid. There's already an effective ban on driving while distracted. If you get distracted by using a hand-held phone while driving, then you should decide not to do it. If you're not distracted, then holding a cell phone while driving is perfectly acceptable. According to the Institute for Highway Safety's report, most New York drivers have decided that they can make their own decision about whether they are distracted or not. New York drivers, if not New York legislators, have decided to repeal the law.