First Minister Mark Drakeford rejects a proposed new £1.4bn motorway in south Wales
He has published a public inquiry inspector's report which backed the scheme to ease congestion around Newport
However, Mr Drakeford revealed the cabinet decided in April the project was unaffordable
'Substantial adverse impacts' on the Gwent Levels wildlife habitat were also a factor, he added
The discussion in the Senedd of the Welsh Government's decision to scrap the proposed M4 relief road has ended, so we'll draw our live coverage to a close too - thanks for joining us.
There will be more reporting, reaction and analysis on the website and on all other BBC Cymru Wales news services as the day progresses.
One business next to the M4 was happy that the relief road had been abandoned.
Roadchef, which runs Magor services in Monmouthshire, had warned it could lead to an 80% drop in westbound custom because motorists would have faced a detour.
It had given evidence to the public inquiry, warning it could even lead to drivers falling asleep at the wheel if they waited too long to take a break.
Simon Turl, chairman, added: "In light of today’s decision, Roadchef is looking forward to working with the Welsh Government to release vital investment at Magor which has up until now been on hold".
Image source, JAGGERY/GEOGRAPHAnita Watts, of Pant Road in Newport, has lived close to the motorway for more than 39 years.
“It has got noisier over the years since we’ve been here. Otherwise I think you learn to live with it.
"I think it’s the wrong decision in some ways. We do need the new M4 relief because of the businesses in Wales.
"I’m sure they could have done a different design further down the line that would miss the wetlands out. I think they need to go back to the drawing board and have another look.”
The Woodland Trust said four ancient woodlands would have been threatened by the building of the M4 relief road.
“One of our priorities is protecting ancient woodlands under threat and the irreplaceable biodiversity that they support, said Natalie Buttriss, the charity's director in Wales.
"We currently have around 70 cases of ancient woods under threat in Wales.
"I sincerely hope therefore that now, with the rejection of the proposed ‘black route’..a change of direction has been initiated which rejects all unsustainable road development and reduces the over-riding threat to our precious woodland habitats.”
Image source, Rory Francis/Woodland TrustThe Woodland Trust said this ancient woodland at Coed Kernew was under threat
Vaughan Roderick
BBC Welsh Affairs Editor
It had become clear over the past few days that the plans for an M4 relief road were heading for the scrapyard.
U-turns aren’t normally allowed on motorways. This case is the exception, it appears.
Mark Drakeford insisted that today’s decision was the result of a changed financial and political context. Part of that change of context though is a change of first minister.
We don’t know whether Carwyn Jones would have given the plan the go-ahead had he taken the decision himself, as he’d intended.
Many suspect that the former first minister regarded the relief road as part of his legacy. If so, today will have been a disappointment for him.
All of which, of course, leaves the people of Newport dealing with the worst congestion problems in Wales with all the inconvenience and pollution that go with that.
That congestion isn’t confined to the M4 though. Newportonians will be hoping that any future measures take in not just the motorway but the A467, the A4042 and the frequently gridlocked city centre.
Rick Dempsey who lives on Pant Road in Newport near the M4.
“I personally wouldn’t like to see them build through the level, it would cause too much irreparable damage...but I see this motorway at a standstill most mornings, especially westbound, so something’s got to be done. What? I don’t know.”
According to First Minister Mark Drakeford, these are some of the "fast-tracked, targeted interventions" we might now see to reduce congestion on the M4 in south Wales:
Newport East AM John Griffiths said he supported the decision to scrap the M4 relief road project, unlike the Newport West AM Jayne Bryant.
He said they agreed on the scale of the congestion problem but disagreed on the solution.
Mr Griffiths described the Gwent Levels as a "unique and historic environment".
The value of that habitat and a climate emergency required "new thinking, more imagination and new ways of approaching these problems", he added.
The AM urged ministers to work with local communities, such as the people of Magor and Undy who were campaigning for a new railway station to serve their villages.
Image source, Welsh AssemblyBrexit Party group leader Mark Reckless scorned the suggestion of setting up another commission, and educating people to avoid accidents, as adequate alternatives to the abandoned relief road.
He said the 2016 Welsh Labour manifesto had promised to deliver an M4 relief road.
That "very clear promise" had now been broken, Mr Reckless said.
Image source, Welsh AssemblyNewport West AM Jayne Bryant said the decision to scrap the M4 relief road was "deeply disappointing".
She said the city was being condemned to "further decades of heavy congestion, idling traffic and toxic fumes".
She asked that the money set aside for the M4 relief road would still be spent tackling congestion in Newport.
Mr Drakeford repeated his earlier insistence that alternative measures would be taken to ease the problem.
Image source, Welsh AssemblyThis business leaders' organisation wants to see improvements at key road junctions in Wales.
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Plaid Cymru leader Adam Price said there would be "many, many alleluias" in response to the Welsh Government's U-turn on the M4 relief road.
He said it would have been "financially destructive", in "siphoning" such a large proportion of public funds.
However, Mr Price lamented the time and money wasted in a decision which he said should have been made years ago, and the money invested in an integrated transport system that Wales "so desperately needs".
Image source, Welsh AssemblyYou've probably read by now a lot about black routes and blue routes. The blue route was an alternative route, backed by transport expert Prof Stuart Cole, which would mean an upgrading of existing routes around Newport.
When it was first proposed at the end of 2013, it was estimated it would cost £380m to bring the A48 Newport Southern Distributor Road and former steelworks road up to standard.
Image source, IWASarah Dickins
BBC Wales Economics Correspondent
So the numbers didn’t add up for the Welsh Government. Despite the fact its own economic appraisal report argued in 2016 that for every £1 spent £2 would be generated by the M4 Relief Road, it has now decided that it is not cost effective.
The argument that if you build more roads you attract more traffic has been around for years, but increasingly the Welsh Government has looked at wider impacts.
The Well-being of Future Generations Act forces the Welsh Government and others to consider the impact of decisions on our health, prosperity and equality. It has also shaken up the way the government views the economy, beyond a simple drive towards more jobs. Now our living standards and quality of life have to be taken into account too.
The Welsh Government will have been well aware that 28% of households in Newport have no car, and would not directly benefit from the investment.
The challenge now is for a Plan B, a viable alternative, to ease congestion and reduce the frustrations of people living in the area.
Following the first minister's statement, Welsh Conservative leader Paul Davies says people have been talking about a solution to M4 congestion for decades, which he described as a "foot on the windpipe" of the Welsh economy.
"We are no further forward", Mr Davies said.
"We need less of your dithering and more action to resolve the challenges facing modern-day Wales."
Responding to the Tory leader, Mr Drakeford said the alternative measures to be followed would take effect far sooner than it would take to build a relief road.
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Mr Drakeford said even if the cabinet had not ruled the project unaffordable, he would still have rejected it on environmental grounds despite an inspector's report in favour.
It would have a "substantial adverse impact" on the Gwent Levels wildlife habitat, and a "permanent adverse impact" on its historic landscape, he told the Senedd.
First Minister Mark Drakeford has begun his statement to assembly members explaining his decision to scrap the M4 relief road.
He spoke of "unprecedented uncertainty" about public funding and Brexit, and said the project would have had an "unacceptable impact" on the Welsh Government's other priorities in transport, health, education and housing.
Click the video link above to watch the statement live.
Image source, Welsh Assembly