Frustration with Queensferry Crossing ice threat is valid – Alastair Dalton

A thermal imaging camera image of the Queensferry Crossing from February 2020. (Picture: BEAR Scotland)

It’s particularly vital if the scheme involves large numbers of people and a route with few viable alternatives.

The Queensferry Crossing is proving to be a classic case.

Much was made of the bridge’s enhanced features which would make it far more reliable than the adjacent Forth Road Bridge it replaced, such as hard shoulders and windshielding.

Minor bumps and vehicle breakdowns could trigger hours of tailbacks because of the difficulties of clearing such blockages. Strong winds would also regularly restrict which vehicles could cross.

By contrast, I recall the wonders of the Queensferry Crossing being talked up by an official, who told me the windshielding was so good, “if you can get to the bridge, you will be able to cross it”.

However, some seem to have misinterpreted the structure’s capabilities and refer to it as “the bridge that will never have to close”, which I don’t recall anyone involved actually claiming.

Fortunately, it turns out that the windshielding – which protects vehicles from winds up to 115mph – hasn’t been the problem and has averted restrictions on dozens of occasions since the crossing opened three-and-a-half years ago.

The northbound diversion over the Forth Road Bridge during last weekend's trial. Picture: BEAR Scotland

Instead, and unexpectedly to non-bridge engineers, the £1.35 billion project’s Achilles’ heel has been ice.

I recall thinking when I got a tip-off two years ago about vehicle windscreens being smashed by falling ice that it must be some freak incident.

I could find just one reference to ice in the official book – The Queensferry Crossing: Vision to Reality by David Watt – in information provided by the Met Office.

It stated: “The new bridge and the surrounding area are susceptible to strong winds and icy conditions, especially during winter.”

In fact, as The Scotsman revealed in 2019, the problem of ice forming on the bridge’s towers and cables, or accretion, had been considered at the design stage.

But Transport Scotland told me it had not been an issue on either the Erskine or Kessock bridges, which are of similar “cable stay” design, and was “very rare in the UK”.

I’ve subsequently been told ice accretion on the Queensferry Crossing requires a specific combination of factors, including temperature, relative humidity, and wind speed and direction.

Nevertheless, ice accretion hasn’t proved to be “very rare”. If anything, it appears to be becoming more frequent.

Since the March 2019 incident – the first we know about – there have been at least three others, in February and December last year, and again two weeks ago.

Potentially icy conditions were also forecast and and snow warnings issued for the next few days, before being lifted, which would have involved ice monitoring and patrols on the bridge – and perhaps a repeat?

With no solution to ice accretion yet identified, there has also been frustration at the difficulty of diverting traffic onto the Forth Road Bridge during ice threats.

It hasn’t previously been possible because of major work on the bridge, but I’m told the first trial diversion last weekend took five hours and 20 minutes to set up.

Perhaps unsurprisingly, the ice situation has prompted exasperation from opposition politicians, issuing slogans such as “national embarrassment”.

That might sounds hyperbolic to some, but it demonstrates the need for expectations to be managed.

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