Manx police have warned drivers of changes to a road during the TT races after a person was stopped driving in the wrong direction.
Mountain Road has been reduced to one-way from Ramsey Hairpin to the Creg-ny-Baa, 24 hours a day.
Insp Mark Britton, of the Road Policing Unit, said enforcement was being "actively and continually conducted".
"The dangers caused by anyone travelling against the one way system are obvious," he added.
The TT festival began on Monday and runs until 10 June.
The Mountain course is celebrating its centenary this year.