TT organisers say they've found 'several sections' of the Mountain Road that need work prior to this year's races.
It means parts of the route will have to shut for nearly four weeks whilst work - including resurfacing, drainage repairs, painting and putting up signage is undertaken.
The DOI says the works will get underway in two phases.
The first will see a road closure from Ramsey to the Bungalow, from Monday, April 3 to Saturday, April 8, with the route between the Bungalow to the Creg ny Baa to remain open.
The department says while it's planned for the road to open ahead of Good Friday, it's weather dependent and can't be guaranteed.
Phase two will see a full Mountain Road closure from Ramsey to the Creg-ny-Baa from Tuesday, April 11 to Friday, April 28.
Tholt-e-Will Road junction will remain open to enable access to the Snaefell Mountain Railway, Snaefell Café and Victory Café.
The closure could be extended until Friday, May 5 in the event of delays due to poor weather or other unforeseen issues.
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