Urgent repairs are needed to Ballagawne Bridge near Kirk Michael.
The Department of Transport has discovered corrosion on the iron girders which support the structure, on the Kirk Michel to Peel Road.
No major work has been carried out on the bridge since it was built, to carry traffic over the old Kirk Michel to St John's railway line.
Extra supports will be installed on either side over the next two weeks, with traffic directed over the centre of the bridge to avoid the weakened area.
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