Maintenance work started this week on the M4 elevated section in west London following problems with the bridge piers.
Netting will be installed around the bridge piers between junctions 1 and 2 of the motorway, near Chiswick.
The netting will retain any debris that could fall from bridge piers, where surface concrete has become loose due to delamination.
The work is being carried out to protect motorists while the Highways Agency and its contractors develop a long term solution to repair the concrete.
The netting is due to be installed at all the bridge piers along the structure between now and the end of January, starting with one near junction 2.
Highways Agency asset manager Paul Robinson said: “The M4 elevated section is a vital route to and from the capital, and we are committed to keeping it operating safely and reliably.
“Delamination is not uncommon in reinforced concrete structures as they get older, and the Highways Agency has a long-standing comprehensive inspection and maintenance regime to manage it.
“The netting being installed will provide extra reassurance for road users by minimising the risk of falling debris.”