Roadworks that are set to bring major disruption to the Avonmouth bridge will have to be repeated after a decade, when the new surface is expected to wear out.

Lane closures, contraflows, speed cameras and traffic jams face motorists using the M5 at Avonmouth for eight of the next 16 months.

The resurfacing work is scheduled on both carriageways of the Avonmouth bridge between now and the start of 2010.

The Bristol Evening Post reported earlier this week that work to resurface the southbound carriageway of the bridge is due to start next Monday night, with months of delays facing motorists until January next year.

Speed limits of 50mph will be imposed while the £7.2-million project takes place.

But the respite will be short-lived, as an identical scheme to re-lay the northbound carriageway is due for the same period at the end of 2009.

And the new road surface, which replaces one last laid as recently as 2000, is only expected to last for 10 years – after which it will be ripped up and re-laid once more.

The steel bridge is flexible and expands during hot weather, so the road surface stretches and breaks more quickly than on concrete bridges.

But despite new asphalt being brought in from Switzerland and a team of Swiss engineers hired to lay it, the new surface is only expected to last a decade.

Around 60,000 vehicles a day drive over the bridge each way, more than 7,000 of which are HGVs, making it one of the busiest motorway bridges in the country. Wet weather, heavy traffic and a thin road surface means it wears out very quickly.

Major structural work and resurfacing was carried out between 1995 and 2000 and now it is needed again.

Highways Agency project manager David Stock said: "We have looked around the world to find what materials are available because we were aware of problems which occurred last time the bridge was re-laid.

"The new Swiss asphalt has greater durability and it will be machine-laid to produce a consistently level surface. The last surface lasted for eight years and we hope this one will last for 10.

"We do expect some congestion and anyone who uses the route regularly will understand how sensitive it is.

"There are existing problems on most Friday nights and we expect that to be the worst time."

Work has been scheduled to start on Monday night, after the rush hour has finished.

A crew of 50 engineers and labourers will work on the mile-long stretch of the motorway, which crosses the Portway and the River Avon.

The project will have four phases, with resurfacing moving across the southbound carriageway, lane by lane, and with the hard shoulders sacrificed both ways to make space for access roads and contraflows.

Speed limits on Avonmouth bridge will be policed by cameras making sure motorists stick to the 50mph limit.