West Sussex council to repair ageing Hazelwick flyover
Vital repairs are to take place on a flyover built 40 years ago - parts of which were only expected to last for 25 years.
West Sussex County Council said if work was not done now the bridge in Crawley would eventually fail safety tests.
Parts of the Hazelwick flyover, which straddles the Hazelwick roundabout, have worn over time, Councillor Pieter Montyn said.
The flyover is due to close for about 16 weeks from 11 February.
A public drop-in session is being held at the Ramada Plaza Hotel in Crawley on Monday when engineers will be available to answer questions.
Mr Montyn said: "It must be stressed that if we do not carry out these repairs now the bridge would eventually fail a safety inspection.
"If that were to happen, we would be forced to shut the flyover to traffic for safety reasons."
He said the parts in need of repair were well past their expected service life of 25 years.
During the £650,000 scheme, diversions will be in place and the roundabout will be reduced to two lanes.
The council said a heavy volume of traffic used the roundabout each day and warned of disruption.
Drivers have been advised to avoid the roundabout where possible while the work is being done.