Junctions on the M4 in Newport could close, and a new bridge built across the Menai Strait, as part of Welsh government plans for two notorious transport bottlenecks.

It will also begin an 18-month project looking at a range of “roads-based” options for the M4, that could include a new motorway or expanding the Brynglas Tunnels.

Ministers are considering whether to close or partially close three junctions, potentially by 2028. However, a review has warned that closing them could cause increased congestion and noise on alternatives routes.

It is not clear at this stage how anything would be paid for – the new Menai crossing could cost up to £700m and take up to ten years.

It is the latest set of proposals to tackle congestion on the M4, after plans for a relief road were developed in the 2010s and axed by former Labour first minister Mark Drakeford in 2019.

In south Wales, the Welsh government is to hold an 18-month study that will look at a range of options for what it says are “road-based solutions” to congestion on the road.

Ministers have ruled out the black route previously proposed for the M4 Relief Road, although it is understood that the study could still include a new motorway south of Newport.

Other options include widening the Brynglas Tunnels – one of the most significant causes of congestion on the M4 in Wales.

The Welsh government also plans a five-year programme of changes to deliver “shorter-term benefits”, including “a delivery plan to improve how the motorway is operated and managed”.

In a statement, the Senedd Deputy Transport Minister Mark Hooper said this could include potential junction closures in and around Newport to improve traffic flow.

“The review found that measures such as these offer some of the quickest opportunities to improve traffic flow and resilience on the M4,” he said.

The government is considering closing junction 27, at High Cross, and east-facing slip roads at junction 26 – Malpas – and junction 25 – Caerleon.

However, firm decisions have not been made and ministers want to consider the impact on local roads, and speak to Newport council, before it goes ahead.

The announcement follows a review by transport consultants at ARUP on some of the options that could be implemented along the M4 corridor, which warned that public acceptance of the junction closures was “likely to be low” among their users.

It said: “There is a risk that economic costs would be redistributed rather than reduced, with poorer access for local businesses and increased congestion, noise and delay on alternative routes.”

“The capital cost would [be] relatively affordable, but the option would likely provide limited long-term value,” the review said, putting the cost at £14m with a 3% estimate of traffic reduction.

The ARUP report looked at eight different options, including new railway stations, a bus rapid transit scheme and road projects.

Widening the Brynglas tunnels, for example, could cost £1.7bn, but pose an “engineering/geotechnical risk” and major construction disruption.

Changes to the A48 and A4810 to increase capacity – known as the Blue Route – are thought to cost £1.8bn, take eight years and reduce traffic on the M4 by 6%.

Other measures backed by the Welsh government include improving the A465 for freight, such as providing facilities for HGVs.

The Welsh government said it would immediately recommence development work for a third Menai crossing.

Plans had been formally scrapped three years ago, although a year later the then Labour Transport Secretary Ken Skates suggested it was back on the agenda.

Officials believe a new crossing could cost around £670m, with development work taking up to two years. It would be at least eight to ten years before the crossing was built.

The A55 is currently carried over the Menai by the Britannia Bridge, and unlike the rest of the road it is a single carriageway.

The Menai Suspension Bridge has been restricted to vehicles under 7.5 tonnes since repair works began in October 2022.

The government has ruled out a three-lane tidal-flow operation on the Britannia Bridge after a review found significant safety and operational concerns.

Deputy Minister for Transport Mark Hooper said “people want action, not endless discussion”.

“They want reliable journeys, less disruption and confidence that government is getting on with improving things and making a difference to people’s lives. And that’s exactly what we’re doing.

“We will carry out an 18-month study to consider a range of road-based solutions for the M4 around Newport. Alongside that work, we are taking action to reduce peak-hour traffic by up to around one in ten vehicles.”