WINSTON-SALEM, NC – More than 20 percent of licensed Americans — amounting to roughly 41 million drivers on the road — would not pass a written drivers test exam if taken today, based on data from the 2009 GMAC Insurance National Drivers Test.

Overall, findings from the fifth annual survey of 5,183 respondents indicate the number of drivers with knowledge of basic road rules is decreasing, with this year's test scores lower than last year's (76.6 percent vs. 78.1 percent).

Idaho and Wisconsin drivers tied for first in the nation, with an average test score of 80.6 percent; New York drivers ranked last, with an average score of 70.5 percent. This is the second time Idaho ranked first and the second time New York has ranked last in the survey's five-year history, according to GMAC.

Idaho and Wisconsin replaced Kansas's 2008 ranking as most knowledgeable; New York replaced New Jersey's 2008 ranking as least knowledgeable.

Respondents continued to have difficulty on questions about yellow lights and safe following distances, while almost all drivers answered correctly what a solid line meant, the GMAC study found.

Top crash-causing driving mistakes reported were multitasking while driving, following too closely, failure to yield on left-hand turn, incorrect merging, and backing up.

Thirty percent of those surveyed say financial strains have triggered a desire to drive less and seek out new ways to save money, according to GMAC.

Click here for additional findings and to see how your state ranked.