The motorway that forms the key route between London Heathrow Airport and the Olympic Park reopened Friday after being closed for emergency repairs, two weeks ahead of the Games.
A stretch of the M4, the main link between inner London and the world's busiest international passenger airport on the western edge of the city, was shut last Friday after cracks were discovered on a bridge.
The section was reopened after engineers completed the "exceptionally delicate and difficult" repairs to a hairline crack in the Boston Manor Viaduct, a Highways Agency spokesman said.
The M4 is expected to be one of the busiest routes during the Olympics, which open on July 27 at the Olympic Park in Stratford, east London.
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.
John Woodcock, transport spokesman for the opposition Labour Party, said the government needed to say it had complete confidence that the route was safe.
"The whole country wants the Olympics to be a huge success," he told BBC television.
"So it is a huge relief that the road is open because of the chaos it would have caused with athletes arriving on Monday to travel to the Olympic Village."