Newly released figures show the 18 Mountain Road was shut for almost 1,100 hours last year.
Data disclosed under FoI revealed the road was fully closed for 486 hours across 39 days.
These closures were attributed to weather, maintenance works, incidents, and event preparations.
A further 608 hours of partial closures, affecting sections between Ramsey and the Creg-Ny-Baa, were recorded over 29 days.
The DoI also said it does not hold specific hourly data for TT and Classic TT/MGP events.