"Significant repairs" are needed for a crumbling bridge in Bath which carries up to 17,000 vehicles a day.
The revamp of the Grade ll-listed Cleveland Bridge would be one of the most important road projects undertaken by Bath and North East Somerset Council, members say.
The council has applied for government funds for the work and is to impose a ban on vehicles over 18 tonnes.
The bridge is a short cut from junction 18 of the M4 and the south coast.
Without the crossing over the River Avon, traffic would either need to pass through busy city centre roads or take a lengthy diversion to the east.
Councillor Neil Butters, who is responsible for transport, said: "The repairs to Cleveland Bridge will require one of the most significant road maintenance projects the council has undertaken for many years and because of this we are seeking the help of the Highways Maintenance Challenge Fund.
"Cleveland Bridge is a historically and strategically significant structure, not only as a Grade II listed structure but forming as it does one of the busiest river crossings in the area. Implementing the weight restriction is a precautionary measure until we find out about the funding."
The weight restrictions will affect about 600 vehicles over 18 tonnes which use the bridge every day.
The proposed work will see:
- Repairs to the concrete truss and strengthening of the concrete deck
- Refurbishment and repainting of original cast iron arches and parapets
- Waterproofing and resurfacing works
The council says the bridge, which was built in 1826 for horse-drawn vehicles and pedestrians, would have to be permanently closed to vehicles over 18 tonnes if the work is not carried out.