A £50m plan to improve the A415 between Abingdon and Witney is set to be abandoned by Oxfordshire County Council.

The scheme had been seen as an important means of diverting traffic from the heavily congested A34 and A40.

The A415 scheme would have been made up of a series of costly improvements, including a Marcham bypass, Kingston Bagpuize Link Road, the replacement of the historic Newbridge and a bypass for Standlake and Brighthampton.

But it now looks like the scheme is an early victim of the regional assembly's South East Plan, which says road schemes linked to new housing developments should be given highest priority.

A report from the county council's head of transport, Steve Howell, says the new criteria mean there is little point in even submitting the scheme in the current round of bids or even beyond 2011.

He is recommending that councillors should now remove the A415 improvements from the county's long-term programme.

He said the decision meant alternative ways needed to be found to manage congestion on the A34.

But the county council is still left with the problem of diverting traffic away from Newbridge, where the 12th century bridge is taking a pounding from heavy lorries using the road.

An 18-tonne weight limit has been imposed, because of the speed of the bridge's deterioration. A 50mph limit has also been brought in along the A415, following a series of fatal accidents.

Mr Howell said that the only long-term solution was to build a replacement.

But it is now likely that any new bridge would be close to the existing bridge, if the rerouting of the A415 is abandoned.

Standlake Parish Council earlier wrote to David Robertson, the cabinet member for transport, about the environmental impact of a new crossing.

Parish clerk David Bevan said: "There are many places where the A415 is unsuitable for HGV traffic, primarily due to the width of the carriageway which creates a dangerous environment for pedestrians and cyclists.

"We have always maintained that the solution is to impose a permanent 7.5-tonne weight limit at Newbridge and route HGV traffic along existing trunk roads.

"This would have the effect of preserving the historic monument and its setting, maintaining the A415 as a strategic commuter route and saving millions of pounds of public money."

He feared that with no Standlake and Marcham bypasses, the amount of traffic at Newbridge would still increase, with traffic levels affecting the quality of life in villages.

County Hall now says it is hoping "funding opportunities" for local infrastructure could arise if Thames Water's plan for a massive reservoir at nearby Steventon goes ahead.