Traffic is being kept off part of the main road between Bitton and Bath where cracks have widened and the road is subsiding.
The severe weather of the last month, which has seen flooding on the road, has worsened the condition of the road near the entrance to Kelston Park. Cracks have also developed in the pavement.
Bath & North East Somerset Council said tonight: “There is erosion of the material under the road surface and the retaining wall. This is due to the intense run-off of water from adjacent land which runs underneath the ground.
“Because of the extensive amount of water over recent weeks, this has destabilised the ground underneath the highway.
“A thorough investigation of the structure underneath the road and retaining wall is taking place. This has included a state-of-the-art ground radar survey to identify the extent of the underground problem, avoiding unnecessary excavations.
“The results will be known by the end of the week. In the meantime, temporary two-way traffic lights will be used to prevent vehicles from running over areas of weak road. During peak times, these lights will be manually operated to keep traffic flowing.
“A further announcement will be made when the council has settled on a course of action.”