Work is due to start this weekend on the installation of de-humidification system to the main cables of the M48 Severn Bridge.
The bridge will be closed to traffic from 6am on Saturday until 6pm on Sunday and further occasional closures are expected overnight until the beginning of June.
During the closures, drivers are advised to use the M4 Second Severn Crossing.
"A programme of cable inspections was carried out on the bridge between April 2006 and January 2007 after corrosion was found in the cables of similar bridges in other parts of the world," said Highways Agency project manager Chris Pope. "As a result we now have a programme of work to install the dehumidification system to the entire length of the cables.
"Safety remains our priority and we can reassure the public that the M48 Severn Bridge continues to operate safely."