The Welsh Government’s South-East Wales Transport Commission (SEWTC) report, published in November 2020, recommended a network of public transport alternatives to tackle congestion on the M4 in south-east Wales. The UK Government’s Union Connectivity Review endorsed these recommendations in full in 2021.

In February 2026 the Prime Minister made a generational commitment to end historic underinvestment in Welsh railways. This included building the six new South Wales Main Line stations recommended by the SEWTC report, creating the additional rail capacity needed to help reduce motorway traffic as set out in that report.

Responsibility for the M4 around Newport, including the Brynglas Tunnels, is devolved to the Welsh Government.

For planned closures on the M4, National Highways will identify and review diversion routes in advance to ensure they are safe, suitable and appropriate for the surrounding road network, including for heavy goods vehicles.

National Highways will agree diversion routes with the relevant local highway authorities, ensure they are clearly signed in line with national standards and ensure they are monitored while in operation. Diversion routes are kept under review and may be amended where issues are identified.

National Highways has a thorough, consistent and documented approach to the management of construction schemes. National Highways assessed the removal of lighting on the M4 between junctions 8 and 12 using TA49/07, which was the assessment tool before TA 501 was published in March 2020. National Highways has published the M4 J3-J8/9 and J10-J12 Road Safety Lighting Review, which included a summary of the personal injury collision data for the 5 years prior to the removal of lighting. Road casualty statistics and the underlying data are published annually by the Department for Transport.

National Highways (NH) is well aware of this issue, and in 2024 treated a site along the M4 that was found to be discharging into the River Lambourn chalk stream near Newbury. More generally, the Department is working closely with NH to address the risk of water pollution from the strategic road network and supports the prioritisation approach taken by NH in its efforts to mitigate pollution. This focuses on addressing verified high-risk outfalls as defined in NH’s 2030 water quality plan. The DfT and NH both recognise the importance of protecting chalk streams and NH is undertaking a review of its technical standard for road drainage and the water environment to give greater prominence to chalk streams.

The Oxford-Cambridge Arc represents a strategic growth corridor with the potential to facilitate sustainable economic, social, and environmental development for the region, and its impact on the transport system is multi-modal. It is recognised that additional analytical work will be necessary to comprehensively assess the interdependencies and areas of alignment with parallel studies, including the M4 to Dorset corridor study.

The Department and National Highways recognises the creation of a proposed new Junction 18A on the M4 to the northeast of Bristol as a priority for South Gloucestershire Council and other local stakeholders. I know the Department and National Highways look forward to working with South Gloucestershire Council on suitable proposals.

The M4 to Dorset Coast Study has been considering how to improve north-south strategic road connectivity between the M4 corridor and the Dorset Coast.

The findings of this study will be reflected in the final RIS3 document when published later in 2024. Rather than a standalone report, National Highways will be in contact to discuss its outcomes with you.

The Department for Transport has no plans to make a comparative estimate of the average contribution to air pollution from vehicles on the M4 and from air traffic at Heathrow.