Roadworks on the A76's Howford Bridge, close to Mauchline, are set to continue until the end of October.
Investigation work began earlier this month due to drainage issues being identified on the bridge.
The works will be carried out along the length of the bridge deck at the low point, adjacent to the kerb, to uncover sub-surface drainage units that will be rodded and flushed to test their functionality.
Amey, on behalf of Transport Scotland, replaced the downpipes beneath the A76 Howford Bridge structure earlier this year, with the work being delayed due to adverse weather conditions.
Now, the current roadworks are set to be in place until at least Monday, October 31.
The single-lane closure will be in effect 24/7 while the works are carried out.
Angus Bruce, Amey bridge manager for the south-west trunk road network, said: “A bridge inspection identified that excess water has been pooling on the bridge from the surrounding land.
"This means the bridge drainage system has been dealing with a much higher quantity of water than intended and this has resulted in damage to the carriageway.
"Our intention is to develop a drainage solution, which will ensure that excess water is being safely directed away from the bridge deck and that any water that does land on the bridge can be dealt with by the existing bridge drainage and waterproofing system.
“While this repair scheme is developed for this structure, temporary traffic lights will remain in place on the A76 Howford Bridge to ensure the continued safety of road operatives and the travelling public.
"We thank road users for their patience and understanding while this essential maintenance takes place.”
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