 The Isle of Man TT is run in a time-trial format on public roads closed to the public by an Act of Tynwald (the parliament of the Isle of Man).The event consists of one week of practice sessions followed by one week of racing.It has been a tradition, perhaps started by racing competitors in the early 1920s, for spectators to tour the Snaefell Mountain Course on motorcycles during the Isle of Man TT on ""Mad Sunday"", an informal and unofficial sanctioned event held on the Sunday between 'Practice Week' and 'Race Week'.