It usually hasn't been very long since young drivers took their tests. But they sometimes behave irresponsibly on the road, forgetting all they've learned

Several American states are wrestling with how to make very young and very old drivers less of a menace on the roads.

Teenage drivers are killing themselves, friends, and other innocent travelers and pedestrians at a tragic rate. States have tried all sorts of things to reduce this carnage, like forbidding novice drivers from traveling with other teens. But the combination of inexperience and speed — and sometimes alcohol or drugs — is leading to funerals for people in the prime of their lives all across the land.

Older drivers are often courteous, and they know the rules of the road.  But poor eyesight and mental lapses contribute to accidents

Old people don't kill on the highways at the same rate, but there are enough crashes involving old folks' medical emergencies, confusion, and bad eyesight that several states want to require not just eye exams but full driving tests for people who reach a certain age.

When the GMAC insurance company gave people the kinds of questions they once took on their driving tests, many people performed miserably

None of this is news to those who must share the roads with the old and the young. But this might be:

A recent online test administered by the GMAC insurance company found that 18 percent — roughly one in six licensed U.S. drivers — would fail their written tests if they took them today. That's twice the rate of failure from just last year. These are ordinary adults, by and large, not very young and not terribly old.

Many states require periodic eye tests when drivers renew their licenses. But they're beginning to wonder whether that's enough to keep highways safe

To get your first license, you take a written test and drive around the block with an examiner. If you do OK, and park the car successfully, you get a driving permit. In many states, your drivers' license lasts a lifetime. You just send in renewal fees every few years and maybe pass occasional eyesight exams.

But if GMAC is right, 36 million U.S. drivers would fail their written tests today. Makes you wonder how they'd do with the driving test!

The results varied greatly from state to state. Drivers in sparsely populated Idaho, in the American West, did best. New Yorkers, in the crowded East, did poorest. Of course, there's no telling what Idahoans' scores would be if those poor folks had to drive the mean streets of New York City.