Drivers are thought to be parking illegally on a main route in Surrey because they do not understand what a clearway is, police have said.
Officers issued fixed penalty notices to 35 drivers for illegal parking on the A30 between Egham and Bagshot near Windsor Great Park in one day.
Roads police community support officer (PCSO) Sam Bernath said it was thought they did not know the clearway sign.
The sign, a red cross and circle on a blue background, means no stopping.
Mr Bernath said local people had said illegal parking was causing serious problems.
He said people usually parked there to avoid paying for parking while visiting Windsor Great Park.
"I believe the main reason people are using the A30 as a car park is because they don't understand what a clearway is," he said.
"A road signposted as a clearway should not be stopped on unless in emergency and should never be used as a place to park a car.
"The signs are there for a reason as it is too dangerous to park and people must take note to avoid a serious collision."
He said Surrey Police would be taking action against anyone who continued to park on the A30 and would be increasing patrols in the area as the weather got warmer and more people visited the area.