THIS month marks six years since the Welsh Labour Government formally cancelled the M4 relief road project near Newport — a decision that continues to divide opinion across Wales.

The proposed six-lane motorway, designed to bypass the heavily congested Brynglas Tunnels, was scrapped in June 2019 by First Minister Mark Drakeford. At the time, he cited the £1.4 billion cost, the ecological importance of the Gwent Levels, and the Welsh Government’s commitment to reduce emissions from transport.

Despite over £150 million of public money already spent on preparatory work and planning, the project was abandoned. It has since become a key battleground in the debate over infrastructure, the economy, and climate policy in Wales.

Welsh Conservatives: “Build it now”

This week, the Welsh Conservatives brought a motion before the Senedd urging ministers to revisit the decision and move forward with delivering the M4 relief road.

Sam Rowlands MS, Conservative Shadow Secretary for Finance, Transport and Infrastructure, said:

“Labour’s decision to scrap the M4 relief road wasted huge amounts of money and was an attack on Welsh motorists.

An M4 relief road would have alleviated traffic demands, whilst boosting our economy and investment into Wales.

Welsh Conservatives will always be on the side of motorists, and that’s why we’re calling for the M4 relief road to be delivered.”

Party leader Andrew RT Davies added that the relief road is essential if Wales is serious about attracting investment and improving productivity:

“We desperately need an M4 Relief Road, to improve transport infrastructure and attract investment into South Wales.”

Labour and Plaid: Environmental costs and funding gaps

The Labour-led Welsh Government has defended its stance, arguing that major roadbuilding projects are incompatible with the urgent need to reduce emissions and shift towards sustainable transport. The decision to scrap the project was reinforced by a wider moratorium on new roadbuilding, introduced in 2021.

Lee Waters MS, then Deputy Minister for Economy and Transport, was clear: “We won’t get to Net Zero unless we stop doing the same thing over and over again. Building more roads to deal with congestion is not a long-term solution.”

Plaid Cymru, meanwhile, has focused on funding, arguing that the UK Government has failed to provide the necessary infrastructure investment. Ben Lake MP told Parliament last week:

“This new money does not come close to the £1.8 billion owed to Wales. And simply, there’s no additional money for road infrastructure and to even revisit things like the M4 relief road.”

How did a road that hasn’t been built cost millions?

Although the M4 relief road was never constructed, the Welsh Government still spent more than £150 million of public money on the project — a figure that continues to raise eyebrows.

The costs stem not from construction, but from a wide range of preparatory and legal work undertaken over several years before the scheme was cancelled in 2019.

A significant portion of the money — over £15 million — was spent on compulsory purchase of homes and land along the proposed route. At least 29 residential properties were bought, some just weeks before First Minister Mark Drakeford pulled the plug. Two houses in particular were purchased in April 2019 for £575,000 and £400,000 respectively.

Millions more went into planning, environmental studies, traffic modelling, engineering designs, and the costs of the public inquiry — a legal process that included months of hearings and hundreds of pages of technical submissions.

Specialist consultants were hired to advise on road design, ecological mitigation, legal compliance, transport economics and flood risk — all of which are standard for major infrastructure proposals. These reports were produced in line with UK Government transport policy requirements and the Welsh Government’s own planning framework.

While no tarmac was ever laid, these upfront costs reflect the extensive legal, technical and bureaucratic groundwork required for a nationally significant road project. As critics have pointed out, hundreds of millions were spent only to cancel the scheme, with no visible infrastructure to show for it.

The properties bought under compulsory purchase are now being managed by the Welsh Government’s property division, with some rented out. However, their long-term use remains uncertain.

The cost of inaction

While some academics have cautioned that road projects can induce more traffic and fail to deliver long-term economic transformation, most experts agree that Wales has already lost hundreds of millions of pounds by not building the M4 relief road — and the costs continue to mount.

The Freight Transport Association warned in 2019 that cancellation could result in “hundreds of millions of pounds in lost private sector investment.”

A 2009 business case suggested the scheme would deliver £695 million in net benefits over its lifetime.

The CBI has repeatedly said that poor transport connectivity is one of the biggest barriers to attracting new business to South Wales.

The Welsh Government’s own 2016 report found that congestion on the M4 imposes significant costs on productivity, freight movement, and tourism — all of which act as a drag on economic performance.

Even critics of the original scheme concede that the current traffic bottleneck at the Brynglas Tunnels remains one of the worst in the UK, with the South East Wales Transport Commission ranking it as the 4th most congested urban motorway in Britain and among the top 50 in Europe.

Despite earlier warnings that the relief road might only offer short-term gains, the economic and logistical price of inaction is becoming harder to ignore.

The motion

The motion brought forward by the Welsh Conservatives reads:

To propose that the Senedd:

• Regrets that this month marks six years since the M4 relief road project was scrapped.
• Calls on the Welsh Government to deliver an M4 relief road.

Labour and Plaid Cymru are expected to vote against the motion, but the debate has once again brought national attention to the M4 corridor’s ongoing transport crisis — and the growing cost of not fixing it.