But he downplayed suggestions of a “design flaw” in the bridge, which only opened two-and-a-half-years ago, but sat empty yesterday as thousands of east coast commuters were forced to make a 34-mile detour.
A “unique” mix of wintry conditions brought on by Storm Ciara was instead blamed for the closure.
No 'single solution'
The Tories are now demanding long-term action to tackle the problem, but Mr Matheson said there was no “single solution” amid calls for heated wires on the cables and towers. The bridge closed on Monday night after eight cars were struck by ice and is expected to re-open this morning, unless the weather takes a turn for the worse.
It has led to widespread disruption for the 80,000 motorists from Edinburgh and Fife crossing the bridge every day who were forced to re-route over the Kincardine Bridge.
The old Forth Road Bridge was not re-opened as the southbound carriageway is being dug up, prompting concerns it would only lead to increased
congestion for motorists.
Mr Matheson said it remained unclear why the ice issue became a problem during some bouts of severe weather, but not others such as the “Beast of the East” two years ago.
He admitted the bridge may be forced to close again as a result of the ice issue.
“We are developing our understanding of these conditions,” he said during a visit to the Queensferry Crossing.
“But it would appear to involve a ‘certain consistency’ of snow, sleet, wind speed and direction, along with fluctuating low temperatures.
“This is leading to an ice formation on the bridge’s towers and cables at low temperature which has subsequently fallen from the bridge when thawed,” he said.
Asked if there could be a flaw in the design of the bridge, Mr Matheson said: “I don’t think it is possible to say that ... during construction when there were adverse snow and ice periods, there wasn’t a problem with snow and ice building up on the cables.” A similar ice build-up did lead to lane closures when it happened last year and the minister said the issue would be further investigated.
Bridge engineers and designers have been carrying out investigations in an effort to identify where the build-up of ice had been taking place, particularly whether it was on the cables or on the tower.
The proposal to introduce ice sensors on to some parts of the structure came about as a result of that work.
That has now gone out to procurement exercise, the transport secretary said, with the installation of the sensors expected in coming months.
Lack of action
Tory Transport spokesman Jamie Greene accused Mr Matheson of a lack of action following last year’s problems.
“Despite repeated promises by SNP ministers that falling ice would not be an issue, the first sign of snow this winter and the bridge is closed to traffic in both directions for a significant period of time,” he said. “Questions are now being asked as why this issue hasn’t been addressed despite it being known about last winter.
“As usual, the SNP is quick to cut ribbons and stick flags on things when there are still major technical safety issues.
“Be it roads, bridges, ferries, trains or planes – whatever it is the SNP touches seems to end in financial or logistical disaster for the tax-paying public.”
The Tories suggested the possibility of “heated wires”, used elsewhere in the world, should be looked at.
The Scottish Government insists the crossing is far more resilient than the Forth Road Bridge and has remained open on 30 occasions when its predecessor closed, usually due to high winds.
First Minister Nicola Sturgeon said the Queensferry Crossing was necessary despite its impact on vehicle emissions because Fife “needed a reliable crossing”. She said: “It’s the first time it’s been closed since it was opened, because it is much, much more reliable than the crossing it replaced.”
Ice sensors are due to go in the next couple of months, but will only help identify the problem. Ice is only identified at the moment through visual inspections by bridge staff.
Liberal Democrat MSP Alex Cole-Hamilton, whose Edinburgh Western constituency covers the southern end of the bridge, called for publication of a delayed bridge review.