Engineers are investigating what could be a major fault in a bridge carrying Gloucester's northern bypass.
The project should ease traffic congestion on the A430 Bristol Road
The problem could delay a government plan to hand over responsibility of the A40 bypass to the local council.
The bridge is supported on piers as it crosses low-lying land and the east parting of the River Severn just a few yards from the Over Roundabout.
A surface ridge has appeared and experts fear it could be caused by the distortion of the underlying structure.
The A40 along with the A48 is due to be downgraded to a county road, but Shire Hall says it will refuse to take over a section which needs costly repairs.
The Highways Agency is due to hand control to the county council this summer.