Plans to use the Forth Road Bridge as a key route for public transport are being undermined by a failure to put in place promised improvements, according to campaigners.

Transform Scotland said using the bridge as a public transport "corridor" would not work as only three of 18 planned projects intended to support the scheme have been completed.

The future of other elements of the plan including bus lanes and a park and ride site in Livingston, is uncertain, it said.

The sustainable transport charity's director was speaking as the neighbouring Queensferry Crossing opens officially as a motorway on Feb 1st. The change means non-motorway traffic will now join buses on the Forth Road Bridge (FRB), which is now to be used exclusively for buses, taxis, pedestrians and cyclists.

Colin Howden said efforts to cut bus journey times will result in failure if bus lanes on the A8 and A90 and other public transport infrastructure is not there to support it.

He welcomed the fact that the pedestrians, buses and cyclists were being given priority on the FRB, but said there was no sign that several major commitments were progressing.

Criticising national transport agency Transport Scotland, and the Scottish Government, he said the missing improvements posed a "serious threat" to hopes of faster and more frequent public transport services for commuters between Fife and the Lothians, and also to desired reductions in congestion and air pollution.

Mr Howden said: "The bridge on its own doesn't deliver a 'public transport corridor' as ministers claim.

"But journey times into Edinburgh won't improve significantly until public transport priority is put in place at either end of the bridge and not just on the bridge itself. Unfortunately, most of the major commitments made by Transport Scotland towards public transport investment have not materialised, notably A8 corridor bus priority measures, improvements in bus priorities between Barnton and Edinburgh, or a new bus park & ride site at Livingston.”

A spokesman for Stagecoach, which runs most of the buses using the FRB said efforts to tackle road congestion were "vital" to encourage people to leave their cars at home.

A spokesman for Transport Scotland said an updated strategy to be published later this year would indicate which projects had been delivered, which abandoned, and the timescale for taking the remainder forward.