ENGINEERS are poised to put a multi-million pound prefabricated tunnel under the M4 motorway as part of Swindon's Front Garden development.

Traffic would be taken from the Croft Road area of Old Town along what would effectively become a southern relief road, running parallel to the M4 before swinging under the motorway 80 metres to the east of the railway line by junction 16.

The scheme is the first serious attempt to connect parts of south Swindon with Wootton Bassett Road in the west of the town.

The £4m, 70-metre tunnel forms part of a wider and ambitious plan to build 4,500 houses on land sandwiched between Swindon and the M4 on land that has become known as the Front Garden.

Bryant Homes will submit its tunnel scheme to Swindon planners on January 24 next year.

Les Durrant of Old Town-based DPDS Consulting, the lead consultants for the Southern Development Area, said: "The contractors would actually build the structure alongside the motorway embankment and excavate the tunnel area accurately and precisely.

"The road construction is only one part of the Southern Development Area proposals, which we hope are in early in New Year.

"Compared to other developments of same scale, the Southern Development Area is a leading edge proposal and probably the most sustainable development of its kind in the UK.

"It will provide much-needed housing for the Swindon workforce to continue the successful economy of the town."

A system of complex steel wires fed through the tunnel and back over the top of the structure allow the rectangular tunnel to glide through while providing support to the earth and carriageway above.

The prefab tunnel is a relatively new engineering technique and has been used under the M1 motorway at junction 15a near Northampton.

But the scheme has angered environmental campaigners.

A spokesman for the Campaign for Rural England said: "There are many objections to Swindon's Southern Development Area, but the proposal to tunnel under the M4 stands out as one that puts a question mark over claims that the development is sustainable.

"Instead of being a road that connects up with the rest of Swindon, this tunnel proposal will bring more traffic into Swindon.

"What will a new road do for bottlenecks in Old Town and rat runs along Hay Lane and Wharf Road?

"Will it encourage commuting along the M4, cut off as the Front Garden is from the rest of Swindon by the railway and escarpment?

"Although it may be perceived that a new road would relieve pressure on other roads, notably through the Lydiards, this relief might only be temporary.

"Experience has shown that more roads generate more traffic and more development."

Last year the Front Garden Action Group lost its battle to prevent Swindon Council from pressing on with plans to allow developers to build thousands of houses on the 700-acre greenfield site.

To date the action group has paid more than £32,000 in its legal battle to thwart the development.

Fionuala Foley (Con, Old Town and Lawns) said: "The more I look at traffic schemes for the Front Garden the more I think this is not a suitable area for development it is just going to be horrendous."

gsheldrick@newswilts.co.uk