ONE in five road signs and markings are a mystery to drivers, according to a new study by Kwik Fit.
Astonishingly, only 10 per cent of motorists knew that longer white lines in the middle of the road indicated a hazard ahead.
And only a quarter were aware a blue round sign with the number 30 crossed by a diagonal red line signified a minimum speed limit while one in four Londoners did not know the sign for congestion charging.
The study by the auto repair firm showed that the majority of drivers believed the driving theory and hazard perception tests should be retaken throughout people's motoring lives, with more than half (53 per cent) thinking it should be repeated at least once every 20 years.
Roger Griggs, communications director at Kwik Fit, said: "Although many of us think we are good drivers, we are ready to accept that we don't know the meanings of all road signs.
"Our research showed that some surprising results, and indicated that there are some clear instructions and safety warnings which drivers are not picking up on when out on the road.
"While people can't be expected to voluntarily retake their test, it would be a good idea for even those of us who have been driving a long time to make sure we really do know the correct meaning of road signs and markings."
The other signs which were most unknown included the white circle with a red border, which means all vehicles except bicycles being pushed by a pedestrain are prohibited, the sign for country parks and the windsock symbol warning of crosswinds.
The national speed limit sign - 60mph on single carriageways and 70mph on dual carriageways - was recognised by only 81 per cent of drivers and only 91 per cent knew the no entry sign
According to the Kwik Fit study, which quizzed 2,000 adults over the age of 18, two-thirds (68 per cent) of UK adults believed that drivers should have to re-take the driving theory and hazard perception tests, with an average gap of every 15 years.
Those who do currently drive would leave a longer period between tests, on average every 16.5 years, while non drivers believe motorists should be retested every 11 years.
The signs shown in the image which caused the most confusion were:
A - Give way ahead B - No entry for vehicle including cycles C - Level crossing without a barrier D - National speed limit applies E - Hazard ahead F - Beware of cross winds G - End of 30mph minimum speed H - Congestion charging zone ahead I - All vehicles prohibited except bicycles being pushed by pedestrians J - Country park