Work was overseen by the Connect Plus consortium of Balfour Beatty, Atkins, Skanska and Egis Road Operation under its Area 5 contract with the Highways Agency.
The Highways Agency described the work as “an exceptionally delicate and difficult operation to repair cracks.”
The job was due to be completed yesterday and the Agency came under intense media and political pressure following the delay.
It confirmed this morning that the motorway has now reopened between junctions 2 and 3 to all cars.
The Highways Agency closed the motorway last Friday night after a new crack was found in a highly stressed part of the bridge supports.
This required a unique repair solution involving the manufacturing of bespoke specialist steel plates and their installation over the crack.
The crack then had to be removed to prevent further damage to the structure. This intricate part of the operation took several hours – even though the crack was a hairline one.
The crack was discovered during an ongoing repair programme.
Work on that continues and for this reason vehicles weighing 7.5 tonnes or more will still be restricted from using the motorway between the junctions. A diversion route remains in place via the A4 and A312 dual carriageways.