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 alternative 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 10 years to be built
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.
The government said that Transport for Wales (TfW) would provide support to "accelerate delivery" of train stations in Cardiff Parkway, Magor and Undy stations.
Proposed junction closures were criticised by the city's council leader, Dimitri Batrouni, while the Tories and Reform called for the Welsh government to get on with an M4 Relief Road.
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 motorway.
Ministers have ruled out the black route previously proposed for the M4 Relief Road - a new motorway south of Newport along the Gwent Levels.
However, 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, 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 review put the cost at £14m would reduce traffic by an estimated 3%.
"The capital cost would [be] relatively affordable, but the option would likely provide limited long-term value," the review said.
Asked by Casnewydd Islwyn Labour Member of the Senedd Jayne Bryant how other Newport junctions would cope, Hooper said: "This work isn't just one piece of work that makes the difference.
"So, alongside any junction closures will be improvements in public transport, will be improvements in the flow of roads that go between those junctions as well, which should make life easier in many ways."
Local resident Wendy Panting said: "It's horrendous.
"We can't get out, we live just on the side of the M4 and we can't go east or west at any time of the day. We've lived with it for a very, very long time and there's been congestion at certain times of the day, morning and evening, but now it's all day.
"Something has got to be done because you can't move around here. The congestion is just far too much."
Roger Panting said he did not think there was "any other way around it".
"I think it's going to become increasingly gridlocked. It's gridlocked already and I don't see anything other than that [an M4 relief road] as being the solution," he said.
"I mean you can tinker around with it, delay it all. But unfortunately until you get a new relief road, Newport's going to be a major problem."
Leo Quiqley said it was all a bit confusing.
"It was a bit of a song and dance about it, before there was talk of it happening," he said.
"And then it obviously got cancelled again, so it would feel like a waste of their time if they're just going to spend 18 months deliberating it only to then just say 'oh well we're not going to do it again'."
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.
Hooper said the government would invest in wind deflectors, variable speed limits and other improvements on the bridge.
But he said: "These measures will not replace the need for a third crossing."
The government promised to accelerate existing plans for new stations at Magor, Undy and Cardiff Parkway.
Rail is not devolved, although the UK government has already pledged £445m for new rail stations.
Hooper told the Senedd that a new Network South East Wales board would oversee delivery.
"I have asked the team to prioritise delivery of the Cardiff Parkway and Magor and Undy stations so communities can begin to benefit from these investments as quickly as possible."
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."
Labour's Newport council leader, Batrouni, said the proposed junction closures were a "bitter pill" for residents impacted.
"We will totally be doing we can to challenge the Welsh government and Plaid's decision on this.
"It adds a great traffic burden to the city," he added.
Leader of Reform Wales, Helen Jenner, said: "Plaid's answer to the M4 congestion problem appears to be moving the traffic around and closing junctions rather than solving the problem."
She added: "Reform believes the M4 relief road remains the only credible way to provide additional capacity and take pressure off the existing motorway."
Welsh Labour spokesperson for transport, Vikki Howells, said: "It's taken the Plaid government five months to realise there's a traffic problem in Newport - and now it's taking them another 18 months to come up with some answers."
She said all Plaid seemed capable of "is yet another review".
"Ministers should now devolve this decision out to local leaders, so people in Newport aren't made to wait even longer for action."
Natasha Asghar, of the Welsh Conservatives, said: "Closing important and well-used motorway junctions will simply move congestion around and clog up A roads and other city streets rather than creating additional road capacity."
She welcomed the wider package of measures, including progressing new train stations, but added: "None of these are a substitute for a long-term solution to the fundamental capacity problems on the M4 around Newport, which can only be addressed by increasing capacity. The best way to do this is to build an M4 relief road."
Green MS Paul Rock welcomed the package of measures and that TfW would be delivering new stations.
If you rely on the M4 in south east Wales for work, you'll know how unreliable it is.
Whether you're a commuter heading for the office or at the wheel of a delivery lorry, the sometimes tortuous trundle through Newport has drivers in despair.
The dim light being dangled at the end of the Brynglas Tunnels by the transport minister may bring some hope, but Hooper's already into the expectation management phase of this announcement.
Whatever solution is chosen will be based on "robust evidence" and a "clear understanding of what can realistically be delivered", he told the Senedd.
So while the short-term interventions may lead to junction closures and public transport improvements, the long-term fix is unlikely to be a new toll-road motorway.
Commuters across the Menai Strait have a firmer idea of their future. A commitment to a third crossing now needs a design and a budget that will allow it to be built this side of 2040.
"Doing nothing is not an option," Hooper told his colleagues in the Senedd.
Drivers in north and south Wales, already frustrated at the pace of change, will be hoping that the wheels of government move more quickly than their own.
