NEW YORK (CNN/Money) - When faced with a written test, similar to ones given to beginning drivers applying for licenses, one in ten drivers couldn't get a passing score, according to a study commissioned by GMAC Insurance.
The GMAC Insurance National Driver's Test found that nearly 20 million Americans, or about 1 in 10 drivers, would fail a state driver's test if they had to take one today. GMAC Insurance is part of General Motors' finance subsidiary, GMAC.
More than 5,000 licensed drivers between the ages of 16 and 65 were administered a 20-question written test designed to measure basic knowledge about traffic laws and safety. They were also surveyed about their general driving habits.
Drivers in the Northeast and mid-Atlantic states did worst. Twenty percent of test-takers failed there.
The state of Rhode Island leads the nation in driver cluelessness, according to the survey. The average test score there was 77, just eight points above a failing grade.
Those in neighboring Massachusetts were second worst and New Jersey, third worst.
Northwestern states had the most knowledgeable drivers. In those states, just one to three percent failed the test. Oregon and Washington drivers knew the rules of the road best. In Oregon, the average test score was 89.
According to the study, many drivers find basic practices, such as merging and interpreting road signs, difficult.
For instance, one out of five drivers doesn't know that a pedestrian in a crosswalk has the right of way, and one out of three drivers speeds up to make a yellow light, even when pedestrians are present, the study said.
Drivers not only lack basic road knowledge, but exhibit dangerous driving behavior as well.
"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," said Susan Ferguson, senior vice president of research at the Insurance Institute for Highway Safety.
One out of 10 drivers regularly exceeds the speed limit by 11 or more miles per hour, with drivers aged between 18 and 24 years showing the greatest propensity for speeding, the study said.
Speeding increases both the likelihood of an accident and the severity of the crash, the company added, citing research from IIHS.
Younger drivers are the most likely to fail a written driving test while those between the ages of 50 and 64 are the most likely to pass.