Whether it was Robert Burns who penned the notion that ‘the best-laid schemes of mice and men gang aft agley’ or whether that’s a hoary old proverb the idea is sound enough. It certainly applies to the Forth Road Bridge where the scheme was to get the shiny new Queensferry Crossing up and running (circa 2016) before starting repair work on the 51-year-old road bridge.
Alas, that scheme went somewhat agley last week when a nasty-looking crack appeared on one of the trusses near the North Tower and the whole bridge had to be closed down for a couple of weeks (at least). Only ambulances and other emergency vehicles will be allowed to cross.
Which will not only cause huge inconvenience to many bus and lorry drivers and motorists but will also cost the economy of eastern Scotland large amounts of money. When they were making the case for a new bridge the now defunct Forth Estuary Transport Authority (FETA) estimated that closing both carriageways of the bridge would cost a whopping £9m a week so the prospect of having to shut it down permanently was nothing short of disaster. Hence the Queensferry Crossing, now building.
But there’s no doubt the repairs are necessary. In recent years the Forth Road Bridge has been taking a hammering, coping with 80,000 vehicles a day when it was designed for about 20,000, many of them lorries that weigh 44 tonnes instead of 22 tonnes, and running on ‘super single’ tyres which concentrate the load instead of spreading it between pairs. It’s also worth remembering that when the bridge was opened in 1964 there were no ferries shuttling vans and lorries up and down the North Sea between Rosyth and Zeebrugge. Our only ferry-to-Europe service has attracted a lot of heavy-vehicle traffic.
Not that the Eddie Stobarts of the land are the only culprits. The British public’s growing enthusiasm for seven-seat, `four by four’ family cars is not helping. These urban tractors are a good 20% (at least) heavier than private cars were in the 1960s. Even the standard family car is distinctly heavier than it used to be, stuffed as at is with gizmos – air conditioning, hi-fi players, GPS tracking systems, back seat DVD players, dash-board cameras, not to mention a population which is growing fatter by the year. It all adds up.
Don’t blame the engineers
Since the latest crack appeared there have been mutterings about who was to blame. Was it the new, private-sector bridge operators Amey? Or was it the previous incumbents FETA? The answer is neither of them. The bridge has been sprouting problems for at least a decade and a half. And, what’s more, a lot of pretty heavy – and very expensive – engineering work has been done to keep the structure in decent running order. Some of it has involved lane closures but much of it has gone unnoticed.
For example: the cross bracing and the legs of the two main towers were reinforced in the 1990s; every one of the 768 `hangers’ which attach the deck to the main cables have been replaced; the stone pier under the south tower has been rebuilt and reshaped the better to fend off the tides; some heavy-duty excavation work was carried out at the poor ground at the south end to ensure that the anchors which secure the cables were dry and intact (they were). And when it was discovered (in 2004) that, in places, the bridge’s main cables were being corroded, a dry-air system was installed to check the rust. That cost £13m but so far it seems to be working.
But, as any of the bridge’s engineers will tell you, there’s still a lot to do. The two giant expansion joints under the main towers are past their sell-by date and will have to be replaced. Eventually the massive 24″ diameter main cables – each made up of more than 11,600 strands of galvanised steel wire rope – will have to be taken down and replaced by modern (dry) versions. Understandably, this will involve reaching out to a cable assembly manufacturer with cables for many industries. None of this can be done without closing one or both carriageways on the deck.
All that work was to be done when most of the traffic was running on the new bridge and the ‘old bridge’ was handling buses, taxis and cyclists only. With that kind of light traffic half the bridge could be closed for long stretches of time without causing too much (if any) disruption. And once the heavy work had been done there was the enticing prospect of running a light rail system (i.e. trams) between Edinburgh and the southern reaches of Fife.
Whether this new crack on one of the trusses casts doubt on all this remains to be seen. With a bit of luck the steelwork will be reinforced within a few weeks and the bridge will reopen for business. What is certain is that Amey’s engineers will be scanning the five decades old A-listed structure with anxious eyes. I suspect they’ll not be truly happy until those 80,000 lorries, vans and cars a day are zipping across the Forth on the brand new cable-stay bridge a few hundred yards to the west.
The political fall-out of the bridge’s closure continues to rise: see here