Repairs costing around £100,000 need to be made to Beeding Bridge in Upper Beeding to make it safer for the public.
Following a routine safety check, West Sussex County Council found the bridge needed strengthening so buses and heavy vehicles can continue to cross it safely.
If the work is not carried out, the county council says it would be forced to put weight restrictions on the bridge or, if deterioration was to continue, shut it completely.
The bridge will be closed for five weeks from Monday, January 20, for the refurbishment to take place.
The footbridge adjacent to Beeding Bridge will remain open so pedestrians can still cross.
A signed diversion is being put in place for motorists along the A283 between Upper Beeding and Steyning.
Residents who want to find out any more information about the works are invited to a public drop-in session, which is being held on Wednesday, January 15 at the Old Tollgate Hotel (Gate Room), The Street, Bramber, Steyning, BN44 3WE.
It takes place between 6pm and 8pm.
Officers from West Sussex County Council and contractor Balfour Beatty will be on hand throughout the evening to answer questions.
County Council Cabinet Member for Highways and Transport, Pieter Montyn, said: “This is a task which has to be done.
“We apologise for any inconvenience this may cause while the bridge is closed.
“However, we feel it is much more preferable to shut it for five weeks while works take place, rather than allowing it to deteriorate and cause greater disruption in the long term.”
Bus services provided by Brighton & Hove Buses and Compass Travel that normally serve Upper Beeding and Bramber will be suspended for the duration of the works. A free shuttle service will be in operation between Upper Beeding, Bramber and Steyning where the service will connect with the regular services provided by Brighton & Hove Buses and Compass Travel.