Construction of a new dual three-lane motorway to the south of Newport, from junction 23 of the existing M4 to junction 29, in order to replace the existing motorway which suffers severe operational and congestion problems.
This solution has been chosen partly because widening the M4 and bringing it up to modern standards would be prohibitively difficult - in particular with regard to the Brynglas Tunnels and the twisting alignment.
Unlike previous proposals for an "M4 Toll", which would have been a tolled alternative built in parallel to the M4, this road will be free to use and will replace the existing M4. The present motorway route will be downgraded to an all-purpose road and may be opened up to new access points and development.
The new motorway's £1bn cost represents the biggest capital project ever undertaken by the Welsh Government. In order to fund it, restrictions on borrowing by the Welsh Government have been amended.
The public inquiry for this scheme began on 28 February.
With the recent government announcement that tolls on the M4 and M48 Severn Bridges will be abolished next year, the funding model for this project is presumably changing.
- Welsh Government: M4 Corridor Around Newport
- Welsh Government: M4 Corridor around Newport - the plan
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With thanks to Gerry McKenna, Michael Pritchard for information on this page.