M1 fire: Southbound lane to reopen - Highways Agency
At least one lane of the southbound carriageway of the M1 in north London could reopen by the afternoon.
The Highways Agency said engineers at the Mill Hill site were hopeful a lane could be opened at 1600 BST.
The motorway has been closed southbound between junctions 1 and 4 since a fire started in a scrapyard beneath the motorway on Friday.
Steel pillars have been put up beneath a bridge which was badly damaged when the fire caused concrete to explode.
Engineers said it was a "miracle" the bridge had not collapsed because of the extent of fire damage.
The Highways Agency had initially planned to reopen a part of the southbound route on Monday morning but work to reinforce the bridge delayed it.
"We are working in very difficult conditions in a confined space and have encountered unexpected difficulties in manoeuvring some of the large and heavy equipment required to reinforce the bridge deck," it said in a statement.
Roads minister Mike Penning, a former firefighter, said the intense heat from the fire had seriously damaged the concrete bridge making it "seriously unsafe".
"It was so intense that some of the concrete has exploded and some of the steel has expanded which has made the concrete drop away," he said.
"The inside lane on the hard shoulder was so badly damaged it is beyond repair and we'll have to do remedial work on that later on."
About 200 tonnes of steel support pillars are being used to support the bridge.
Two lanes on the northbound carriageway of the motorway were reopened over the weekend. The full seven-mile stretch between junctions 1 and 4 may not fully reopen until next week.
The minister said the aim was to open two southbound lanes and try and operate a contraflow using the hard shoulder on the northbound carriageway.
Paul Watters, the AA's head of roads and transport, said tens of thousands of motorists had seen their journeys disrupted.
Motorists have been advised to check the Highways Agency website for the latest traffic information.