From: http://www.bbc.co.uk/news/uk-england-london-18751083

*M4 motorway London to Heathrow section closed*

The main motorway link from London to Heathrow Airport has been closed
to all traffic after a crack was found in a "sensitive area" of the
road structure.

The M4 is shut between junctions one and three and is not expected to
reopen until Thursday morning.

Large vehicles were already banned from the elevated section, known as
the Boston Manor Viaduct.

The Highways Agency said it expects all work to be finished before the
start of the Olympic Games later this month.

The full closure of the motorway in both directions between Chiswick
and Feltham began at 20:00 BST on Friday.

*Vital route*

Restrictions on vehicles weighing more than 7.5 tonnes had been in
place since March when hairline cracks were discovered in some of the
steel beams.

The agency said on Friday workers "found a further crack in a
sensitive location which requires us to keep the viaduct closed until
the repair is complete".

Jon Caldwell from the Highways Agency warned there would be delays.

Diversions have been put in place along the A312 and the A4, and the
A40 is expected to be congested as well.

"The repair works that we need to do, to bolt the plates to the
decking, needs to be done with no traffic on it," Mr Caldwell told the
BBC.

"We need to do it now so that it's all completed ready for when the
Olympic traffic starts to use the road in a few weeks' time."

The M4 is the main route between Heathrow Airport and central London
and will be vital for transporting visitors into the city for the
Games.

It is also the major road link from London to the West Country and
Wales, as well as being a heavily-used commuter route.

Just before Christmas, the Hammersmith Flyover - part of the same
route in and out of the capital - was closed for five months after
defects were found with its structure.