A FORMER bridge builder has branded the Queensferry Crossing "a national disgrace" and warned that its design will mean the crossing will never work to its full capacity.

John Carson, who is a former head of Miller Civil Engineering, had previously argued that any new crossing should be a tunnel.

He hit out at the new structure following Tory MSP Dean Lockhart's comments that Fifers were being "let down" by constant delays and restrictions.

"It is a national disgrace," said Mr Carson. "It is just not performing to the promises that the Government made when they decided to build it.

"It is all to do with the road design – motorways are designed to flexible standards. The recommendation for motorways are to have long merging areas and areas where, if you have got a road joining, then the other traffic is meant to be dispersed over a length.

"The bridge and the constraints of the physical area means these motorway standards have been reduced and by reducing them, they have more or less introduced bottlenecks.

"The merges of traffic on the north side from Rosyth and Inverkeithing are too near the crossing and there is insufficient weaving lengths to merge the traffic safely, therefore it is forced to slow to a near stop.

"The south side is worse. You have the same problem with the traffic from Queensferry and Bo'ness but you have the added problem that because one of the lanes on the southern side is dedicated to Bo'ness and Queensferry, drivers use this lane to shortcut the bridge traffic by using the dedicated lane, going round the roundabout and down the bridge slip road, thus further frustrating the problem."

Mr Carson, from South Queensferry, said traffic reports highlighted the issue regularly.

"When you look at the mobile phone, it shows a red line to the centre of the bridge going north and then to the south then the traffic is running freely – the reason for this is this merging problem.

"The other issue is no-one goes at 70 mph. People are down to about 40 mph. That is another issue – the bends coming into the bridge on the north side are not bends you can take at 70 mph so if you are coming from Dunfermline, you come in and the bends that take you around Admiralty are quite sharp and you have to drive with confidence to take them at 70mph.

"Then you get hit with merge on the left going south so the whole thing is an absolute disgrace. We spent all of this money on this new bridge and the traffic is no better at all."

A Transport Scotland spokesman played down Mr Carson's concerns.

“Nearly 80,000 vehicles use the Queensferry Crossing each day and, since opening, there have now been over 20 occasions when it remained open when the Forth Road Bridge (FRB) would have been closed or restricted," he said.

"This clearly demonstrates the new bridge is delivering its clear and intended economic benefits for both industry and commuters, a fact recognised by the road haulage industry.

“Options for both bridge and tunnel crossings, including comparative costs, were considered as part of the Forth Replacement Crossing Study which was carried out between August 2006 and June 2007. This study concluded the best option would be a new bridge crossing; this option was widely supported and endorsed with cross-party support with the passing of the Forth Crossing Act in 2011.

“The design of the slip roads on and off the bridge at either side are in line with motorway regulations and are substantially longer than those on the FRB. The level of congestion witnessed on the M90 over the Forth is completely consistent with the increased volume of traffic across the trunk road network during peak hours. However, performance is monitored and improvements will be made where possible.

“The journey time data we reported last year showed traffic flows to be closer to what is be expected for a road of this type and speed limit.”