By David Hooks

This article first appeared on the website of Politics Scotland (www.politicsscotland.scot) and is reproduced here by kind permission of the author.

There have already been cries that the SNP should have done more, usually from the same people who argued they shouldn’t have built a new bridge and that it was a vanity project. There were claims that the transfer of the bridge maintenance contract to a private company had led to the chief engineer leaving the loss of years of knowledge. But the crux of the argument is that the SNP removing tolls has reduced the money available for maintenance and there were indeed plans to improve the structural integrity of the trusses that were supposedly deferred due to budget constraints. The work to replace the trusses was to be difficult, expensive, originally estimated at £10M but likely to be higher, and cause significant disruption to bridge users. It was decided to try a reinforcing technique with a trial due to finish this year with a decision taken after the transfer of the authority if the trial was unsuccessful.

The Forth Estuary Transport Agency did say in 2014 that the deferral did increase the risk of the long term structural integrity of the bridge, but there didn’t seem to be any urgent warning of "the bridge will collapse in 12 months if you don’t act now". But reality is that the need for work on these trusses has been known about for 6 years. The SNP may argue that the capital budget was cut 25% from Westminster, but the cut to capital grant for the FETA was 65%.

The defect was found during routine inspections, and Mark Arndt, from the maintenance contractor Amey, explained that these types of sheer fractures are difficult to predict and happen very quickly. He noted that significant over-stressing over the lifespan of the bridge had meant several parts of the main supporting structures were carrying far more load under certain circumstances than they were designed for.

But there have been accusations that an increased number of abnormal loads have been allowed across the bridge in the past 12 months and there are many instances of drivers using the bridge in adverse conditions. Some trucks have overturned while traversing in high winds putting increased shock and pressure on the bridge’s structures. An acoustic monitoring system was installed in 2006 and from then to April 93 cable breaks had been identified, but 24 of those had occurred in the previous three months.

But it’s worth taking a look briefly at the history of the bridge. It was first built with an estimate of a maximum of 60,000 vehicles a day, but that number is regularly exceeded, and the maximum weight of vehicles on British roads has doubled to 44 tonnes. At the time of building it was hugely ambitious and was briefly the largest bridge of its kind outside of the United States. It was opened in 1964, yet it was only in 2004, 40 years later, that the first full scale investigation of the cables was performed. During that maiden inspection, prompted by the discovery of corrosion in the Severn bridge, it was discovered that the cables had the corrosion levels of a bridge 20 years older than it really was. A major and expensive, but brilliant, engineering effort was undertaken to dry out the cables. This involved wrapping them in neoprene and pumping in dehumidified air with the aim of stopping the corrosion.

Other work has been done on the bridge over the decades, the towers were strengthened in the 1990’s to cope with increased traffic, and structures were erected to protect them from collisions from ships. This wasn’t dealt with in the original design and there must be increasing questions about the original design and materials used given the number of works that have been carried out.

The size of the crack and the apparent shifting of the supporting structure seems to suggest a major problem that will require months of work to safely repair and will likely lead to expensive inspection and repair work on the other similar sections of the bridge. Given that the new bridge was due to open at the end of next year it may have been thought that the government could get away with reduced investment, but it now seems likely the trusses will have to be replaced.

There is certainly an argument to made that the value of the Forth Road bridge to the Scottish economy has been significantly undervalued and that it has suffered from a lack of investment and maintenance historically. It is also true that the SNP have put the money it to build a replacement, albeit a cut down version of the original plan which would have carried rail as well as road traffic. But there is certainly evidence that the current problems could have been avoided and questions have to be answered

UPDATE:

Derek MacKay MSP, the Scottish Government transport minister, confirmed that the specific fault had not been previously identified as a risk. The closure of the bridge when the fault was found has, he claimed, ensured that the repair will be quicker and less costly.