The M4, one of London's busiest roads and a key route from the city to Heathrow Airport, has partially reopened following emergency engineering work.
The stretch of road between junctions one and two has reopened in both directions, although it is still closed between junctions two and three and is likely to remain so for the next three days.
The motorway, which serves as the key route to the West of England, was closed on Friday night for ongoing repair works to the Boston Manor Viaduct, after cracks in an essential structural area were discovered.
Drivers travelling into west London are being advised to travel via the M3 or M40.
London-bound traffic will be able to join the M4 at junction two and traffic heading out of London can stay on until junction two, although there is a lane two closure in this direction.
A spokesman said: "We expect the ongoing programme of repairs will be completed to enable the viaduct to operate in its full capacity in time for the London 2012 Olympic Games later this month.
"The closure is a sensible precaution, given the bridge's importance, both for people driving to and from west London and for the Games.
"The works are being carried out underneath the structure so the scale of the work is not visible from the M4 or from the local road network."
Diversion routes are in place on the A312 and the A4, which run adjacent to the bridge.