Exclusive:Queensferry Crossing may close far earlier when ice falling from cables forecast

The possible earlier diversion of traffic onto the adjacent Forth Road Bridge follows a car windscreen being hit by ice during Storm Bert eight days ago, which triggered the fourth such closure in four years.

Bridge patrols are deployed to spot ice falling from the cables before the crossing is shut, but the new plan could see that happen as soon as an ice forecast is received - which could be hours before.

Such “ice accretion” only occurs when there is a specific combination of weather conditions, including temperatures of around 0C and particular levels of relative humidity, wind speeds and wind direction.

Queensferry Crossing officials said the problem, which also affects bridges abroad, may never be solved.

However, they are concerned at how quickly ice fell after it started snowing in the November 23 incident, and said new automated barriers could switch traffic between the bridges in as little as 14 minutes.

Patrols were mobilised at 6am because of a forecast risk of ice, and snow started falling at 8am, but traffic was not diverted until after the car was hit about 10.20am.

However, if similar conditions were forecast again, the bridge might be closed the previous night.

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Nick Forbes, south east major bridges manager for BEAR Scotland, which operates the crossing for the Scottish Government, said: “At the moment, the strategy is to be reactive because we have never had full confidence in the forecast.”

He told The Scotsman: “I now know the severe weather forecast resulted in an ice accretion event. So if that exact thing happens again, I’ll be saying to Transport Scotland that I think we should pro-actively close as these are the same conditions we had before.

“We had the weather forecast the previous evening of the risk of ice. The change would be to just forget about waiting and implement the diversion. But we need to trust the forecast 100 per cent and don’t want to be diverting traffic if there’s not going to be an [ice] event.”

Mr Forbes said the incident had happened despite the cables being cleaned two years ago, but that was never expected to completely remove the risk.

He said: “The cable cleaning was always a project to reduce the likelihood of ice, it was never to eliminate it. We’re never going to solve the ice problem. Realistically, we can only reduce it.

“From experience elsewhere in the world, no one’s eliminated it.”

However, Mr Forbes said the latest incident might have been much worse if the cables hadn’t been cleaned, and their next cleaning may be brought forward.

Stewart Mackie, Scotland road safety manager for the IAM RoadSmart motoring group, said: “The safety of those using the Forth bridges must be a priority. As weather conditions in Scotland can change very quickly, it is important any solution can be implemented quickly and effectively to minimise disruption whilst ensuring road safety is at the heart of any plans.

“Transport Scotland must ensure that these diversions are well publicised and communicated in good time.”