In London, a Red Route is a designated Priority road, on which there is no parking or stopping allowed. The yellow lines have been replaced by red lines. In 1994 parking offences were decriminalised, and responsibility for enforcing them is being transferred to local councils; however, Red Routes are still patrolled by squads of traffic wardens, who are controlled by the police and magistrates. There is a £60 fine for transgression.

Outside London it may have a different meaning, for example an accident-prone stretch of road. One definition is "routes in which two or more people have been killed or seriously injured every year for three consecutive years, over a 1000 metre stretch in rural areas or a 500 metre stretch in urban areas." These are the top focus of accident prevention, and amber routes are those with a less serious record but which might become red if left unchecked.