The M48 Severn Bridge will be reduced to single lanes while the cables are inspected for corrosion.
The routine inspections by the Highways Agency are scheduled to start in February and end in October.
During this time there will be a permanent lane one closure westbound, some lane closures eastbound and a 50mph speed limit for safety reasons.
Installation of a dehumidification system in 2007 revealed corrosion of the wires which make up the cables.
A Highways Agency spokesman said: "The programme of cable inspections on the 43-year-old bridge began in April 2006 as a precautionary measure after corrosion was found in the cables of bridges of a similar age and construction in the USA, Japan and many other parts of the world."