Route saw snow and freezing temperatures overnight
The Mountain Road and the upper section of the Tholt Y Will Road are to remain closed until at least midday tomorrow (Thursday 20 November).
The Isle of Man Constabulary confirmed the decision has been made 'for the safety of the general public as well as for those maintaining the roads and those responding to incidents'.
Officers reiterated the 'closure is enforceable, and entering closed roads is an offence'; adding 'please don't put yourself and others at risk'.
The Creg Ny Baa back road is said to be 'passable with care for four-wheeled vehicles but dangerous for motorcycles'.
Meanwhile, a yellow weather warning for frost and ice will remain in force on the Island until 3pm on Friday (21 November).
Doctors accept three-year pay offer
Seven acts promulgated in final Tynwald Day ceremony before election
Sharp rise in data breaches on Island, says Information Commissioner's Office
Footage circulating on social media 'now an active investigation'
Annual Tynwald Day celebrations to get underway