M4 motorway reopens after repairs M4 motorway: reopened to traffic early of Friday after engineers completed 'complex' repairs, the Highways Agency said. The M4 motorway in west London has reopened in both directions a week after it was closed for emergency repair work. The road, which is expected to be one of the busiest routes during the Olympic Games, was shut last Friday between junctions two and three after cracks were discovered on a viaduct. It was reopened to traffic just after 5.30am on Friday after engineers completed the "complex" repairs, the Highways Agency said. The work on the bridge supports of the Boston Manor viaduct had been due to be completed on Thursday. A Highways Agency spokesman said: "An exceptionally delicate and difficult operation to repair cracks in the Boston Manor viaduct on the M4 has been successful and the motorway has now reopened between junctions two and three to all cars." The hairline crack was found on a highly stressed section of bridge supports by engineers carrying out other repairs on the busy section of road. "This required a unique repair solution involving the manufacturing of bespoke specialist steel plates and their installation over the crack," the spokesman said. 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. He said the other repair work would continue, which meant vehicles weighing 7.5 tonnes or more would still not be able to use the motorway between the junctions. A diversion route remains in place via the A4 and A312 dual carriageways. Drivers are thanked for their patience during this complex work. The M4, which is the main route from London to Heathrow airport and the west of England, was initially closed between junctions one and three, causing problems for thousands of motorists. It is expected to be one of the busiest routes during the Games because it links London and the Olympic Park in Stratford with Heathrow. The motorway will officially become part of the "Olympic route network" on Monday, with one lane of each carriageway reserved for competitors, officials and sponsors. Drivers have been warned the network will include temporary changes, including suspended turns, stopping and loading restrictions, and traffic signal alterations.