Study: millions of U.S. drivers don't know rules of the road.

One in 10 drivers in the United States would fail a driver's test if tested today, according to a study by GMAC Insurance. Also, 29% of drivers who drink admitted they would knowingly drive while over the legal limit "if they felt okay."

In the survey of 5,000 licensed drivers, the study found many drivers have problems merging, yielding, staying under the speed limit and knowing when to make a left-hand turn. Many are not serious enough about the dangers of drunken driving, according to the study.

Areas where respondents showed a lack of knowledge also are common causes of highway accidents, according to the Insurance Institute for Highway Safety. For instance, the institute's research shows speeding increases both the likelihood of crashing and the severity of crashing. Since 1997, about a third of those drivers killed in passenger vehicles have had a blood alcohol concentration above 0.08%, which is illegal in every state.

"As a nation of drivers, we've made little progress in the past 10 years to curb some of the most dangerous driving behaviors, including drinking and driving and speeding," Susan Ferguson, senior vice president of research for the institute, said in a statement.

Gary Kusumi, chief executive officer and president of GMAC said, the test supports "the need to stay abreast of the current rules of the road, and to put them in practice each and every day."

The survey found drivers 18 to 24 were most likely to fail a written driver's test, with a 78% passing rate. Drivers 50 to 64 were the most likely to pass, with an 85% passing rate. Drivers in the Northeast and Mid-Atlantic were the least knowledgeable; one in five were unable to pass the written test. Drivers in the Pacific Northwest and Great Lakes were the most knowledgeable, with a failure rate of 1% to 3%.

The study also found:

* One in five drivers does not know that a pedestrian has the right of way at a marked or unmarked crosswalk. One in three drivers claims to speed up when they see a yellow light, even when pedestrians are in the crosswalk. According to the IIHS, 48% of all pedestrian injuries and 21% of all fatal pedestrian injuries occurred in collisions with motor vehicles at intersections.

* The nation's least knowledgeable drivers (those in the Northeast and Mid-Atlantic) are the most likely to speed. Nebraska drivers are the least likely to speed. One in 10 drivers regularly drives more than 11 miles over the speed limit, although 58% of all drivers feel that driving 10 miles an hour over the limit on an interstate is dangerous.

* Half of all drivers say they do not know how to merge into heavy traffic.

* 60% say they change lanes on a highway without using their blinker.

* One in five drivers does not know that highways are most slippery just when it starts to rain after a dry spell.

Would You Drive Drunk?

Given a short distance, drive     29%
themselves home carefully

Give their keys to a friend       26%
and have them drive home

Call a cab, friend or             25%
spouse to pick them up

Wait until they were completely   15%
sober or spend the night

Walk home                          9%