Stockbridge footbridge is to be reinforced with column stiffeners to allow it to open by early September.
Two full overnight road closures are planned on Saturday and Sunday from 8pm to 6pm on the A27 with diversions via the A285, A286 and the A259.
A dedicated westbound left lane closure will be in place until Monday, September 3, along with a 50mph speed limit westbound between Whyke roundabout and Stockbridge roundabout.
Works include ‘column stiffeners, footpath works and painting to allow the reopening of the footbridge’, a letter to residents said.
Works from Monday, August 20, to September 3 will be ‘off network’.
A Highways England spokesperson said: "We are sorry for the delay. During our routine testing we identified an issue that could cause the walkway to move unacceptably in certain conditions.
"We have been looking at engineering solutions that reduce this movement to allow safe and comfortable use of the walkway over the bridge.
"We still expect to open the new footbridge as soon as this work is complete."