Discontent rumbles on as ageing bridge feels the strain of corrosion and traffic.

Leading architects have ignored the controversy over the potential environmental impact of a second Forth road bridge and called for an international competition to design a new crossing linking the Lothians to Fife.

Experts say that if given the go-ahead, a new bridge could be one of the most important civil engineering and architectural challenges of the decade for Scotland.

The existing Forth road bridge is an infamous traffic blackspot, and additional concerns about corrosion affecting its likely lifespan have revived discussions about a second crossing. But with a estimated cost of £500 m or more, and environmentalists warning of the huge impact it would have on traffic levels and pollution, the proposed second bridge is not universally popular.

Writing in the Scotsman, Green MSP for Lothians Mark Ballard said: “it makes far more sense to take measures to lengthen [the existing bridge’s] lifespan and make the alternative routes work better for both commuters and freight. Reduce wear and tear by reducing traffic levels and there will be no need for a second bridge.”