Police say they will deal with motorists 'robustly' if they are caught driving on closed roads.
Officers say they have received numerous complaints - particularly about drivers using the Tholt y Will Road and Peveril Road in Peel.
Peveril Road was closed last week after the road collapsed.
The Department of Infrastructure says it was due to a void forming along the line of the sewer which was made worse by the recent wet weather.
Repair work started yesterday - a diversion is in place while the work is carried out.
Night-time maintenance to shut bridge
Mountain Road shut until Saturday
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Mountain Road closed until 3.30pm