Commuters using one of the most traffic-choked sections of the M5 motorway can expect four months of roadworks and congestion as work to resurface the Avonmouth bridge gets under way again.

Just over seven years after a £125-million revamp, work will begin on Monday to resurface the southbound carriageway of the iconic bridge on the outskirts of Bristol, at a cost of £7.2 million.

The bridge, which carries about 120,000 vehicles a day, is a vital link for tourists heading to some of the UK's most popular spots in Somerset, Devon and Cornwall. It is also renowned for being one of the most notorious traffic blackspots in the region.

As the Western Daily Press revealed in September 2006, major problems with waterproofing on the road on the bridge have left Highways Agency (HA) chiefs with no option but to rip up the existing surface and completely re-lay it.

It is seen as a major roadworks programme including strict 50mph speed limits and the number of lanes cut from four to three lanes in both directions.

HA officials yesterday warned commuters to expect delays and allow more time to get to their destinations while the work, which is scheduled to last until January 2009, is undertaken.

It also emerged yesterday that work to resurface the northbound carriageway is not expected to begin for another 12 months – meaning one half of the bridge will be resurfaced a full year before its counterpart gets the same treatment.

There was fury among road users and people living close to the bridge as work to add extra lanes and to strengthen the bridge ran almost continuously between 1995 and 2001. Work should have been completed by 1999 but a series of problems beset the project causing delays.

Now motorists and residents face months of renewed woes as the resurfacing work on the 1.4km-long, 34-year-old structure is carried out 24-hours-a-day.

Highways Agency project manager Dave Stock said staff would work around the clock to lay the new surface.

Mr Stock said: "Some resurfacing work was done when the fourth lane was put in and strengthening work was done between 1995 and 2000. That surface is now at the end of its shelf life. Because of the amount of traffic running over it, it has expired. We're asking the materials on the bridge to do an awful lot of work."

Water penetrating the surface had been causing the surface to break up and cause potholes on the carriageway. The existing surface will be replaced with the Swiss-designed 'Gussasphalt' material which Mr Stock said would be impervious to water, have greater durability and me machine laid to produce a consistent level that would reduce the amount of planned maintenance in future.

"It will be machine-laid this time rather than hand-laid with Swiss teams coming over to help carry the work, he said.

Mr Stock said there was no ideal time to carry out the work but the scheme was beginning now that the summer rush and the August bank holiday were over. He said: "The M5 is very important to the economy of the South West so it wasn't appropriate to do the work over the summer. We identified that the best time would be the third quarter of the year."

Residents living in areas near the bridge had the chance to attend exhibitions where they could quiz Highways Agency staff about the work, while leaflets explaining the works were also being sent out in the post.

For more information, e-mail ha_info@highways.gsi.gov.uk or telephone 08457 504030.