The Department of Infrastructure says it wants to keep an extension to the Manx Electric Railway terminal in Douglas.
It's applied for planning permission to keep the extra facilities which were approved five years ago.
At the time, the Department of Community, Culture and Leisure was given permission for staff facilities and secure parking at the site.
But the approved plans were only for five years, and the DOI now faces a November deadline to remove the temporary structures.
In its application the DOI says it wants to vary the condition that puts a time limit on the development.
The new application would mean it could continue to use part of the Summerland site for another five years.
It adds the proposed redevelopment of Summerland may still happen, but the Derby Castle Depot still needs the space.
And it says the extra room is critical to running the railway.
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