Fears about a "catastrophic failure" of a bridge prompted council leaders to kickstart up to £50m of repairs.
A report said the Cumberland Basin in Bristol was "no longer approved in the UK for any new proposed highway structures" due to high safety risks.
Bristol City Council members are due to approve an initial £4.25m for inspections and maintenance for the works.
Repairs are expected to last five years.
The report said the degradation of the structure and other nearby elevated roads were "accelerating" and that the final bill and timescale would only be known once the inspections had been completed.
The Cumberland Basin carried two-and-a-half times the volume of traffic anticipated when it was built, the report added.
The estimated cost for repairs to the road network is envisaged to be between £40 and £50m the Local Democracy Reporting Service (LDRS)said.
"The Western Harbour regeneration project intends to deliver affordable homes in this sustainable location, while modernising the wider transport network and a resilient flood defence system instead of simply replacing the network as is," the report stated.
It added that the "continuing ongoing deterioration" of the Cumberland Basin's roads was "now accelerating" despite the council spending £250,000 to £500,000 a year on maintenance.
The report said part of the cost would be met by underspends in other capital projects while funding would be sought from the West of England Combined Authority and the Government.
Work will be staggered over the next three to five years.