NEW sensors failed to give enough warning to shut Scotland's flagship road bridge before ice fell causing potential danger to motorists, the Herald has been told.

The Queensferry Crossing connecting Edinburgh and Fife was closed to vehicular traffic in both directions at 4.45am on Friday after patrol staff noticed ice falling.

It is the third winter in a row that falling ice has plagued the £1.35bn crossing and the second time it has been forced to shut down.

Trunk road maintenance firm Bear Scotland said that a weather sensor system reported "conditions conducive for ice formation" several minutes before the ice fell.

But it was only after the ice had fallen that the road was shut for four hours, it was confirmed.

The development came a month after transport secretary Michael Matheson suggested lessons had been learnt from last winter's issues which saw ice fall onto cars for the second time in a year.

Scottish Labour transport spokesman Colin Smyth said: “The safety of bridge users must always come first, but the SNP government’s excuse that the Queensferry Crossing keeps having to close due to the wrong kind of snow and ice has become a national embarrassment.

“The new sensors may now be able to tell us when there is a problem, but the public are rightly frustrated that the SNP government is no further forward finding a technical solution to minimise or clear such a dangerous build-up of ice.

“This is just the first flutter of snow this winter and the fear is bridge users may well have more closures to look forward to.”

Conservative Mid-Scotland and Fife MSP Dean Lockhart said: "Last year, the Scottish Government promised that the installation of new ice sensors would prevent the issue reoccurring, however we are yet again in the situation where the ‘wrong type of ice’ has caused massive disruption. It is not acceptable.

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

"We need a long term solution to this problem, including allowing use of the Forth Road Bridge."

Transport Scotland was previously criticised for lack of action after reports of ice falling on vehicles in February.

It said it was now looking to extend the use of the Forth Road Bridge to all traffic in instances when the Queensferry Crossing is closed due to the danger presented by ice build up.

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

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

HeraldScotland:

And at the start of last month it announced efforts to prevent the issue with ice sensors installed.

Infrastructure 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 for a second successive year.

In February eight vehicles were damaged before the crossing was closed for the first time since it opened in 2017 on safety grounds.

It led to lengthy tailbacks as drivers take a 35-mile diversion, crossing the Kincardine Bridge.

Calls were then made for an urgent investigation into ice issues on the 1.7 mile publicly funded bridge which arose 11 months after giant icicles smashed the windscreens of three cars after they snapped off from cables on the crossing.

The Herald previously revealed that the problem came despite an existing multi-million pound sensor system being unable to properly detect ice.

At the start of November, it was confirmed that ice sensors had been installed on the Queensferry Crossing as "part of a number of measures to improve the detection and management of ice accretion".

As the new measures were announced Mr Matheson said: "Our teams always look to learn lessons from previous winters and have once again worked hard throughout the year to ensure we are well prepared for when the worst of the weather arrives.

"This ranges from the use of new technology, like ice accretion sensors and motorway access units, to trialling new treatments and adding more gritters to our fleet."

At the time of the February incident, Mr Matheson said there had been a similar issue the previous winter when snow and ice built up on some of the cables, but the bridge had not been closed.

Mr Matheson said: "I recognise the frustration of travellers today, and I very much regret that the bridge has been closed for the first time, but it is a bridge that's given us much greater resilience than the old Forth Road Bridge.

"There's now been something like 30 occasions when we would have had only partial or no use of the Forth Road Bridge, whereas the Queensferry Crossing is continuing to function."

The Scottish Government then confirmed that it was planning to install ice sensors on the structure "in the coming months".

Chris Tracey, Bear Scotland’s south east unit bridges manager, said: “The safety of bridge users comes first and we therefore made the decision to temporarily close the Queensferry Crossing when we identified a risk of falling ice.

“We constantly monitor conditions on the Queensferry Crossing in real time using a bespoke system of weather sensors on the towers and deck. At 04:30 this system reported conditions conducive for ice formation. Patrol staff observed ice falling from the bridge towers shortly after this and the bridge was closed at 04:45.

“We apologise for any inconvenience caused to road users by this closure.”

Bear Scotland said of the new detection system: “The new ice sensors on the Queensferry Crossing will not stop ice forming, however they will improve our understanding of the issue and give us some early warning when conditions are conducive to ice accretion.

“The sensors monitor four weather conditions we know can cause ice accretion when they converge within specific parameters. This will help to provide early warning of such conditions and allow us to more accurately measure and understand the conditions."

A Transport Scotland spokesman said: “Safety of road users is paramount and the decision to temporarily close the bridge was taken to ensure the safety of road users during poor weather conditions.

“Our operating company have an agreed procedure to deal with such incidents having been alerted by the weather forecast. They are able to monitor conditions on the Queensferry Crossing in real time, using a bespoke system of weather sensors on the towers and deck - and were undertaking patrols in advance to monitor conditions.

"Due to ice/snow accumulation and incidences of falling ice from the bridge’s towers, the decision was taken to close the bridge for public safety.

“Work is currently ongoing on the Forth Road Bridge to replace the original bespoke expansion/movement joints, with only the northbound carriageway currently open under contraflow as a public transport corridor. This work is expected to be complete in the coming weeks, and when complete will permit the Forth Road Bridge to be used as a diversion route if required.

“Working with our operating company we are planning to test the process of switching traffic over between both bridges - with a view to being able to make the switch in advance of adverse snow and ice conditions in future, where forecasts indicate there is a high risk of ice accretion issues on the Queensferry Crossing.”