Mr Drakeford cited the cost of the project, which was expected to be more than £1.4 billion, and the environmental impact of the new road on the protected the Gwent Levels, as the reason for binning the scheme.

This decision, however, goes against the findings of the public inquiry - which cost £44 million - recommending it was “in the public interest” for the scheme to be given the go-ahead, and it “would not have any disproportionate adverse impacts.”

It was also revealed today by the minister for economy and transport, Ken Skates AM, that the scrapped project had so far cost the Welsh taxpayer £114million in total - including the aforementioned inquiry costs.

(First Minister Mark Drakeford. Picture: Simon Galloway/PA Wire.)

The planning inspector Bill Wadrup submitted his full report on the proposed scheme in September 2018, addressing the cases for and against the relief road, and looking at the possible alternatives.

Mr Drakeford received this report in February.

Here is an outline of the key points of the 559-page report.

Mr Wadrup's overall conclusion of the report:

“In my view, there is a compelling case for the scheme to be implemented in order relieve an acute problem on the strategic motorway network.

“It is accordingly my view that the scheme is in the public interest… and should be allowed to proceed despite the sensitive landscape and environment through which it would pass.

“The scheme would not, to my mind, have any disproportionate adverse impacts. In coming to this view, I have had regard to my observations of the area and the site, all statutory and non-statutory objections, representations and statements made in writing and oral presentations to the Inquiry, but individually or collectively, they do not outweigh the conclusions I have reached.

“I have also had regard to the cases set out for all the alternatives proposed by objectors, to the support for the alternatives and the counter-objections against them made at the Inquiry or in writing, but individually or collectively, they do not outweigh the conclusions I have reached in respect of those alternatives.”

The cases of the supporters of the scheme:

(Variable speed limit. Traffic on the M4 during morning rush hour, Newport.)

A key argument made by supporters of the relief road was that the congestion around the Brynglas Tunnels was a major barrier to economic growth.

The M4 around Newport serves critical economic factors, connecting the whole of South Wales to England.

Mr Wadrup commented: “Support from industry and commerce, with responsibilities for mass employment widespread across South Wales, is strong and detailed.

“I conclude that the published scheme could be constructed before any of its rivals and that there is compelling, deep and widespread support for the scheme from industry and commerce.

“In my view, the magnitude of and reasoning behind such support carries significant weight.”

He also noted the impact that the project would have on public transport in the area, removing congestion and reducing delays for bus companies and releasing the pressure on the SDR.

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Another argument highlighted by the report was that congestion must be relieved and accident figures would be reduced.

The report highlights that there was an average of four to five accidents on the affected areas on the M4, with motorists sitting through four “normal traffic jams” at the Brynglas Tunnels each day. It also states that when traffic is flowing “speeds throughout the working day are below 50 mph.”

Mr Wadrup commented: “I am convinced would substantially reduce personal injury accidents as well.

“Without the scheme, the evidence points to traffic conditions substantially deteriorating relative to today’s already unsatisfactory situation and, in all probability, the South Wales economy suffering further.”

The cases of the opponents of the scheme:

(Protest against the M4 relief road outside the Senedd on Tuesday, December 4, 2018)

Cost was one of the main objections to the planned relief road. There were worries about the £1.4 billion total cost, and also concerns that this would take money away from other public projects.

The report stated that the project would have been funded through a combination of UK Government borrowing and Welsh Government transport budgets. Some of the additional works which were found to be necessary within the Newport Docks would be paid with a contribution from Welsh Government's economic development fund.

Mr Wadrup said that the project would prove good value for money, despite the high cost.

He said: “The scheme, when considered with risk and potential unforeseen developments, would be expensive and cost about £1.4 billion but I am persuaded that the high cost would give a positive economic rate of return, which has probably been underestimated in the evidence, and in removing travel uncertainty, negative perception and reality of frequent motorway delays, might well give a further economic boost to the region.”

He also noted that commenting on the Welsh Government’s distribution of funds was not the purpose of the inquiry.

The environmental impact of the project came under close scrutiny from the First Minister, and was the focus of many objectors to the relief road.

The project would see the potential loss of 105 hectares of land from the Gwent Levels.

(An artist's impression of how the new bridge at Newport Docks would have looked.)

The public inquiry concluded that the environmental effect of the relief road would be minimised as “The line of the proposed motorway would be sited as far north as possible in order to minimise the intrusion into the Gwent Levels.

“This is critical to avoidance and mitigation and means that the line would be close to the existing built-up area, roads, rail line and existing development.”

The planning inspector also notes the “outside of the Gwent Levels significant planting of trees, both screening belts and areas of woodland are proposed,” minimising the visual impact of the road.

Mr Wadrup states that the impact on habitats affected by the construction of the relief road, such as that of the water vole, would be largely compensated for through by the extensions of the reen and ditch network, their improved shapes and better water quality.

With the lower number of vehicles sat stationary in traffic jams, the planning inspector reported that there was likely to be an increase in air quality had the relief road been accepted.

He said: “The scheme would result in a significant improvement in the air quality at 399 properties alongside the M4 and in urban Newport, with about 29,000 properties benefitting.

“Although 1,600 properties would be subjected to a lowering in air quality no limits would be breached.”

Similarly, Mr Wadrup said that in the opening year, about 12,500 properties would see a lowering of road traffic noise by more than one decibel, while about 2,250 properties would have a significant increase in noise.

What were the alternatives?

The alternative solution was the proposed ‘Blue route’, which would see a 50mph trunk road route through improvements to both the A48 Newport Southern Distributor Road and the A4810.

It would avoid much of the Gwent Levels but would demolish the existing well-used pedestrian and cyclist over bridges across the SDR.

It was estimated this would cost £838 million.

Mr Wadrup concluded that it would have “a significant advantage over the published scheme in terms of their limited impact on the natural environment,… but that clear advantage would be offset and, largely balanced by the significant environmental noise, visual and air pollution disadvantage it would bring to a large number of residents in southern Newport.”

Another alternative considered was the widening widening of the M4 and the Brynglas tunnels to provide a dual-four lane motorway between J29 at Castleton and J26 at Malpas and a dual three lane motorway between J26 and J25.

That would include a new westbound three-lane tunnel (one way) at Brynglas with the existing twin-bore tunnels adapted to carry three lanes of eastbound traffic.

The proposal would cost £743m and would take about seven-and-a-half years to complete and would severely delay motorway traffic.

Mr Wadrup commented that this alternative would be preferable for its limited impact on the Gwent Levels and relatively low cost, but said it would not be feasible as “It would cause traffic chaos for the duration of the long construction period.”

So what's next?

A new commission has been set up by the Welsh Government to look at alternatives to the relief road.

The year-long commission, led by Lord Terence Burns, will consider the 28 alternatives to the 'black route' relief road that was rejected on Tuesday.