A PROPOSED alternative to the M4 relief road includes building an underground tunnel costing nearly £10bn.

The public inquiry is examining 22 alternatives to the Welsh Government backed black route, which is estimated to cost £1.1bn.

Put forward by a resident, alternative 20 to the scheme includes building a tunnel from Magor to Castleton which is estimated to cost £9,820million.

“This suggested route comprises an alternative mainline motorway alignment between Junction 29 (Castleton) and Junction 23 (proposed Magor Interchange),” the objectors preferred alternatives report states.

“The majority of the route would be through a 16km tunnel beneath the Gwent Levels SSSI and River Usk SAC. The tunnel would extend from the area east of Church Lane and to the west of J23A.”

The proposal would provide a more direct and faster route between junction 29 and junction 23, it is claimed.

But the report says the scheme would have “significantly greater capital costs maintenance and operation costs” than the black route.

It is argued the alternative would reduce “surface impacts” on the Gwent Levels, but that there would be potentially “significant impacts” arising from the scheme.

“The cost of this scheme would greatly outweigh the user benefits,” the report states.

The proposed black route would be 23km and consist of six lanes, departing from the existing M4 at junction 23A, passing across a new River Usk bridge to connect with the existing junction at Castleton, junction 29. The aim of the scheme is to ease traffic congestion on the M4 between Magor and Castleton and bring the road up to “modern standards.”

Opponents argue the scheme is too expensive, would harm the Gwent Levels and that there are better alternatives.

The public inquiry, which is expected to run until July, is currently hearing 22 alternatives which have been put forward.

Last month, the inquiry heard villagers from Llanfihangel Rogiet, near Caldicot, present the case for an alternative “green route” along with residents from Llandevenny objecting to the black route. Proceeding.