Could an M4 relief road be back on the cards under a Plaid Cymru government?

Plaid Cymru’s leader Rhun ap Iorwerth said before the election that ‘a response is needed to improve traffic on the M4’

14:53, 18 May 2026

Since 2019 the prospect of an M4 relief road seemed to be dead in the water when then-First Minister Mark Drakeford said the road wouldn’t be built.

The problems clearly hadn’t gone away but the talk of any new road to ease congestion ceased.

Then, in the early stages of the Senedd election campaign ahead of May 7’s seismic vote, Plaid Cymru leader Rhun ap Iorwerth told the WalesOnline leaders’ debate he thought there should be work on something to alleviate congestion on the M4.

Mr ap Iorwerth said: “We believe that a response is needed to improve traffic on the M4 around the Brynglas Tunnels.

“Currently we don’t have a plan. What a Plaid Cymru government would do is put that plan together, starting to build the cases and making the case.”

Numerous options had been discussed before, variously named after different colours, and he didn’t commit to exactly what he was suggesting.

When pushed in that debate he suggested Plaid Cymru in government would look for a cheaper alternative route to the plan for a six-lane £1.5bn M4 relief road south of Newport, known as the “Black Route”, which was backed and then ditched by Welsh Labour.

At that stage it was interesting and definitely inspired a lot of debate – especially for those who lose hours of their weeks in traffic jams.

But now those comments are even more interesting with Mr ap Iorwerth installed as First Minister.

The M4 isn’t explicitly mentioned in the document Plaid Cymru published ahead of the election results which detailed what it would do in its first 100 day, but in large green font it does say this: “The Welsh economy is also bursting with untapped potential”.

It was a working theory the Plaid leader brought up of his own fruition in that debate so is clearly on his mind. For our free daily briefing on the biggest issues facing the nation, sign up to the Wales Matters newsletter here.

And like a lot of things that will come up in this Senedd term it’s not just simply what Plaid Cymru want to happen but what they can find support for around the chamber.

His party will run Wales as a minority government and therefore will have to seek support from around the chamber as needed.

Most of the time we expect that will come from parties on the left bloc of politics like the Greens (two members), Lib Dems (one), or even Labour (nine).

However on the M4 there’s every chance it could become something the government teams up with parties to the centre right with.

So let’s just imagine that Plaid does begin conversations about the M4.

Labour’s then-leader Eluned Morgan didn’t want one and nor did the Greens or even the Lib Dems.

Ken Skates is currently interim leader of Welsh Labour so maybe we should park questions about Labour’s position until any permanent leader is appointed.

On top of that the party could well decide to give Plaid some space for a while to suss out their approach.

But there are two parties,who between them have an awful lot of votes and who do want a new road built.

The Conservatives and Reform UK had both made an M4 relief road a central part of their manifestos. Slightly different in approach, granted, but there in black and white.

While Reform UK suggested a toll road the Conservatives said they wanted a relief road but without tolls.

Would either party back plans if it means they will be able to go to their supporters, and into the next election, with a big-ticket item they had a hand in delivering?

It’s not enough to back the idea of a road though.

For it to be delivered it would cost money and that would be in a budget – something Plaid is going to have to get wider approval for given their minority government status.

Would an M4 relief road be enough for both or either party to suck up the pain of what you’d imagine would be a long list of things they wouldn’t agree with in a budget so they could claim credit?

If not then, were the plans revived only to get stuck, it could be the latest logjam for the M4 to face.