The government's £1.3m project to improve the old railway line between St Johns and Kirk Michael is now expected to cost £1.7m.
According to a Freedom of Information request by Ian Kermode, the total capital cost for the scheme is now around £400,000 over budget.
The plan included reinstating the former railway bridges at Glen Wyllin, Glen Mooar and Ballaleece, building on their pre-existing supports.
The scheme aims to support Active Travel and make the trail more accessible throughout the year.
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