The Welsh Assembly Government this week aborted the M4 relief road, proposed to bypass a two-lane section around Newport.

The WAG has come under pressure to build the road, especially when accidents have closed the main transport artery between South Wales and England for many hours.

The scheme’s benefit:cost ratio exceeded 4:1, but Welsh transport minister Ieuan Wyn Jones said on Wednesday: ‘It has become clear the environmental and economic costs associated with the construction of a relief road are prohibitive.’

The construction cost had risen to about £1bn. Local authorities had voiced concerns about the project’s potential impact on other schemes.

The WAG decided tolling new and existing routes was unacceptable because the Severn Crossings are already tolled.

Tolling the new road alone would significantly reduce the scheme’s benefits and raise insufficient funds for construction.

The focus now switches to alternatives including improved motorway junctions, additional rail stations and park-and-ride facilities across the region.

The WAG estimates that carriageway and junction modifications could reduce traffic flows by 7%. Unveiling the National Transport Plan for Wales, Jones also scuppered a proposed new road to Cardiff airport. He suggested the frequency of airport rail and bus services might be increased, while the nearby A4226 would receive ‘substantial safety improvements’.

The WAG will fully implement the Local Transport Act 2008 by 2010 and work with local authorities to increase take-up of bus quality partnerships and quality contracts by 2014. Up to three more ‘sustainable travel towns’ will follow the Cardiff pilot, and a national programme for travel planning is promised by 2011.