The Department of Infrastructure says it won't reveal some of the costs of TT work because it might damage its commercial interests.
A Freedom of Information request asked for details about how much getting the course ready had cost this year.
The DOI said it needed a special vehicle to set up the one-way system on the Mountain Road, and had a contract with a private firm to paint kerbs and put up signs for temporary speed limits.
But it said in both cases it would withhold the information because it was commercially sensitive.
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