Following devolution in 1999 the project was again drawn up by Welsh Government economic and transport minister Andrew Davies in 2004[17] but this was withdrawn in 2009 when the cost estimates had risen by £660m, to a total of £1 billion.

Several experts suggested that a new toll road would be "a white elephant for 20 hours a day", due to the greatly variable traffic levels through the Brynglas Tunnels.

[26] On 15 July 2009, the Deputy First Minister Ieuan Wyn Jones announced that the plans for the M4 relief were to be dropped and replaced by a package of measures to improve the flow of traffic.

[38][39] In April 2013, the Conservative coalition formalised an agreement with the Welsh Government for a £830m interest-payable loan for the construction of the road at 2011 costs.

[18] On 16 July 2014, Wales Transport Minister Edwina Hart said that the preferred "black route" south of Newport between Junctions 23 and 29, including a new crossing of the River Usk, would go ahead despite political opposition.

[40] In 2017, following a manifesto pledge by Theresa May at the 2017 General Election, Highways England removed road tolls on the Severn Bridges.

This was a result of opposition by Associated British Ports who sought an additional £135m for compensation to improve Newport Docks which would have been affected by the Black Route.

It stated that new research was being commissioned to review how increases in road capacity lead to additional traffic (known as induced demand).

[44] In September 2020 there was widespread discussion about the impact of the United Kingdom Internal Market Bill, put forward to transfer powers previously held by the European Union, which would take effect in 2021 after the Transition Period.

As part of improving traffic flow around Newport, the following measures have also been considered: The government also expects the South Wales Metro to relieve congestion on the M4.

[35] The initial enquiry was also seen as flawed after omitting compensation payments owed to Associated British Ports and to HM Revenue and Customs for VAT.

In January 2018 the Welsh Government announced costs would rise by £135m for compensation to improve Newport Docks which would have been affected by the Black Route.

[48] Friends of the Earth claimed that the road would cause great damage to local wildlife habitats as it was planned to pass through the Caldicot and Wentloog Levels, an area of natural wetlands.

They also raised concerns about the large sum of public money that would have been used to fund the project, claiming that it could be better spent improving the local railway network.

[26] After the July 2014 announcement that the scheme would go ahead, Gareth Clubb of Friends of the Earth Cymru called the proposal "utterly unnecessary and terribly damaging".

Matthew Kennerley of ABP said: "We don't think it's a great idea to put the new route through the centre of Wales' most important general cargo port.

We believe there is an alternative route...slightly further north...[which] would still have an impact on the port but to a much lesser extent because it would not be bisecting very important quayside areas.