WORK to re-open the stricken A4 Flyover has reached a 'critical' point with the stretch set to be closed overnight to allow key strengthening work to be completed.

Transport for London (TfL) has been working 24/7 to get the four-lane flyover fully re-opened before the Olympic Games after it was dramatically shut days before Christmas last year.

It was closed for three weeks after engineers found 'serious structural defects' in the 50-year-old structure blamed on saltwater corroding internal cables.

One lane was re-opened in both directions in mid-January for light traffic but the partial closure has caused tailbacks and traffic congestion in and around Hammersmith.

TfL bosses hope the end to the gridlock is near as they step up their repair work with engineers set to instal new tension cables surrounded by wax oil to prevent deterioration and allow easy inspection and replacement if needed.

It means the flyover has been closed between 10pm and 6am since Wednesday and will remain so until Monday, April 30 with the road re-opened at 10am on Saturday mornings and close at 6pm instead of 10pm.

Garrett Emmerson, TfL chief operating officer for surface transport, said: "We are now approaching a critical phase in our race to reopen the Hammersmith Flyover as quickly as possible. This will require a number of overnight and weekend closures to ensure that the works are carried out safely and correctly.

"I would once again like to apologise for any inconvenience that this work is causing and reassure Londoners that we are continuing to work around the clock to complete these vital works as quickly as possible.

"Work to strengthen the five weakest spans of the 16 span structure will be completed in June 2012, well ahead of the London 2012 Games. This will ensure that the flyover can carry full traffic loading during the Games and for many decades to come.

"Following the Games, TfL will return to the structure to strengthen the remaining spans. This work will not require further weight restrictions to be imposed and TfL hope to complete it with off-peak closures and minimal closures to the flyover, causing limited traffic disruption."

Traffic during the overnight closures will be diverted around the Hammersmith gyratory system but people are being advised to use public transport to avoid congestion.

Drivers are still advised to avoid the flyover. For traffic information visit www.tfl.gov.uk/trafficnews  or follow @tfltrafficnews on Twitter.