THE first phase of a multimillion-pound scheme to ease congestion at Portishead's gridlocked motorway junction gets underway next week.

The initial stages of the scheme – which overall is costing £3 million – start on Monday and is being carried out by the Highways Agency.

Work will be carried out to resurface the roundabout, renew the signals and barriers and white lining and replace high friction surfaces on the approaches to the lights.

The work will be carried out between 8pm and 5am each night and is due to be completed by December 3.

Lane closures will be necessary during the work and a speed limit of 20mph will be on force on the roundabout.

A temporary speed limit of 50mph will be in place on the slip roads and there will be some overnight slip road closures.

Highways Agency area performance manager Dave Sledge said: "The resurfacing work is being carried out on behalf of North Somerset Council who are also undertaking other road improvements around the junction.

"By working closely with the council we have ensured all our works take place at the same time, which will minimise disruption to road users.

"The current road surface and signals are coming to the end of their life and require upgrading.

"The new signals are designed to respond to traffic levels and reduce congestion.

"Replacing the existing tungsten lights, which need replacing every six months, with new LED lights with a 15 year life expectancy, will reduce on-going maintenance costs.

"We will also be relocating the signal control boxes, which in their present location present safety issues in accessing.

"On occasions there will be slip road closures and diversions so overnight traffic should allow slightly longer for journeys."

The work is part of a wider package of improvements being carried out in partnership between the Highways Agency and North Somerset Council to improve congestion at the junction.

At peak times traffic can often tail back miles along the Portbury Hundreds – the only main route in and out of Portishead.

The scheme will see a short additional lane will be created on the approach to the roundabout on the Portbury Hundred and the roundabout carriageway re-marked to provide a second lane to get on to the M5.

The northbound slip road on to the motorway will be widened to accommodate this additional lane before merging to a single lane to join the motorway.

On the Portbury side of the roundabout, an additional lane will be created between Portbury High Street and the motorway roundabout.

Changes will also be made to the junction of Portbury High Street, stopping drivers turning right on to the A369.

Traffic lights will also be put at the junction of the A369 to St Georges Hill to make it easier for people in Pill and Easton-in-Gordano to get onto the A369.

A high occupancy vehicle lane will also be created on the A369 to help traffic travelling out of Bristol to the motorway and Portishead get onto the junction more easily.

The lane will run from just before the St Georges Hill junction to the turn off to Portbury High Street.

The lane, being installed as part of the improvements to the Greater Bristol Bus Network, will be available to cars with two or more people travelling and buses.

The work is being partly funded by developer Persimmon as part of a 106 planning agreement drawn up as a result of the huge housing development at The Ashlands in Portishead, together with a grant from Government as part of the Greater Bristol Bus Network major improvement scheme and cash from the council 's Local Transport Plan.

It is expected that the work will be completed by June next year.