A quarter of drivers have been unable to identify the seven common road signs included in a survey by the AA Driving School.
Director Simon Douglas said: "They are all common on British roads, so it's worrying that so many motorists don't fully understand their meaning.
"While strong intuition and an awareness of your surroundings are valuable skills to have when driving, there is no substitute for a sound knowledge of the Highway Code.
"Drivers who don't know what these important signs mean may be putting lives at risk, including their own."
Despite having to pass a theory test, it is younger drivers who struggle most with signs, while those aged 35 or more, who have not had to pass the theory test, fared better.
Based on responses from 2,000 people, the poll found more than three in five could not identify the sign for cycle route ahead.
These were the top five least-recognised signs and the percentage who got it wrong: cycle route ahead (64%); uneven road (42%); hump bridge (22%); steep hill downwards (16%); national speed limit applies (7%).
© The Press Association 2008