Transport bosses admit an ice prevention system for Queensferry Crossing was dumped as too expensive

The Crossing, the result of the biggest infrastructure project in Scotland in a generation, was shut for four hours on December 4 but only after patrol staff noticed ice falling.

And yesterday it emerged that Scottish Government-funded Transport Scotland have reviewed bridges across the world as part of efforts to prevent ice forming on the Crossing.

In a letter to Labour MSP Alex Rowley, Transport Scotland's director of road Hugh Gillies that any viable solution would have to be "bespoke" as there was "no off-the-shelf solution".

When it opened to traffic in August, 2017, the Queensferry Crossing was heralded by First Minister Nicola Sturgeon as "a symbol of a confident, forward-looking Scotland" and a "feat of modern engineering".

READ MORE: Farce Road Bridge: Disbelief as Queensferry Crossing forced to shut yet again despite new ice sensors

Before it opened, bridge operators said the 3.5m high wind shields, would "almost entirely eliminate the need for closures".

Transport Scotland's road maintenance contractor Bear Scotland has admitted that ice prevention measures were not incorporated into the design of the bridge because of the expense.

Ice on the cables was considered as a "potential issue" during the design of the bridge, but Transport Scotland's road maintenance contractor Bear Scotland said it was expected to be a "relatively rare event" with the climate experienced at the Forth.

"Rather than investing in an expensive preventative system that may only rarely be required, it was therefore decided to manage any ice accretion incidents through operational measures – i.e. by closing the carriageway on the rare occasions that it occurred," said Bear.

In November, after new ice sensors were installed "part of a number of measures to improve the detection and management of ice accretion", transport secretary Michael Matheson suggested the administration had learned a lesson from last winter when the crossing, which was the result of the biggest infrastructure project in Scotland in a generation, was closed following reports of ice falling on vehicles.

Transport Scotland's road maintenance contractor Bear Scotland said that a number of system of weather sensors meant it could "monitor and respond to the specific weather conditions that we know can cause ice to form on the cables".

And it said that its understanding of the phenomenon "should continue to improve, as the weather sensors gather data from future incidents".

But it admitted that it cannot prevent ice from forming on the crossing.

"Our long term goal is to develop a solution that will prevent ice from forming on the cables, and the better we understand the conditions that cause this issue, the greater our chances of success," said Bear. "Every bridge has different design details and operates in a different climate, so there is no off-the-shelf solution that is suitable for the Queensferry Crossing – any such solution will be bespoke."

According to original contractor information there was already a multi-million pound real-time sensor system with 2,300 installed, which included the measuring of environmental impact. These include anemometers to measure wind, barometers, rainfall gauges, air temperature and humidity sensors.

Details of the "innovative" system which uses "highly advanced" software also referred to having structure temperature sensors for the steel, concrete, asphalt and stay cables and 'accelerometers' to monitor any movement or vibration.

But Transport Scotland confirmed that the system was not expected to be fully operational until later in 2020.

In October, last year, Mr Matheson, when answering a question from an MSP about resolving the ice issue pledged that sensors "which detect ice accumulation" would be fitted to the bridge and incorporated within the current monitoring system.

In February, after another ice fall, Scottish Conservatives criticised ministers for failing to address the issue earlier saying that "one of Scotland’s most critical transport routes exposes an SNP government in the throes of capitulation".

Bear said that new ice sensors would allow it to monitor the four weather conditions that it is known can cause ice build-up and would "help to give us early warning of such conditions and allow us to more accurately measure and understand the conditions under which any future incidents occur".

Bear added: "It is important to note that ice accretion will still be managed by closing the bridge should it happen again in the way that it has previously."

The Scottish Government is now looking to use the Forth Road Bridge, now being used solely as a public transport corridor, at least in emergencies. This came to the fore in February after concerns were raised over ice falling onto cars on the Crossing during the winter. Calls were then made for an urgent investigation into ice issues on the 1.7 mile publicly funded bridge as it was closed for the first time since it opened in 2017 after ice and snow fell from cables on to vehicles below.

That came 11 months after giant icicles smashed the windscreens of three cars after they snapped off from cables on the crossing.

Bear Scotland in a response to the latest ice fall said that it is confident that they can understand the parameters within which the problems with ice can occur " and we hope to refine this understanding with the help of the new weather sensors on the bridge".

It added: "But the Queensferry Crossing has only been open for three years, so it is possible that there could be other weather conditions, not yet experienced, which could cause ice to accrete in a different way."

It said the phenomenon has occurred during a "particular combination of weather conditions, when wind speed and direction, temperature, dew point and relative humidity all converge within specific parameters".

It said: "In these conditions, wet snow can stick to the cables, freeze and then fall off within the time it takes for a squall to pass through – sometimes in as little as 10 to 15 minutes."

When the bridge was under construction in 2016, then transport secretary Derek Mackay assured the Scottish Parliament that "the decision to build in structural health monitoring as part of the new Queensferry crossing - a first for a UK bridge - is an example of the efforts that will safeguard that essential crossing for the future".

Both Bear and Transport Scotland did not to respond questions about how much the ice prevention system previously considered would cost and what it involved.