The Queensferry Crossing is to be “cleaned” over the next three months in a bid to prevent the bridge from being forced to close due to a build up of ice during the winter.
The £1.35bn replacement for the Forth Road Bridge has been shut three times since opening to vehicles in 2017 due to accretions on the 288 metal cables suspended between the three towers.
Inspection work after the last closure, in January 2021, found a “considerable” amount of dirt had built up on polyethylene tubes encasing the cables.
However, research at a French lab found removing the surface stains prevented wet snow from freezing and sticking to the tubes.
It is now hoped a new jet wash machine can be deployed to blast dirt off the cables and slow the build up of ice later in the year.
Road bosses previously feared chunks could fall off and damage cars on the road below.
The cleaning of the cables will take place over 12 weeks, with work starting on the south tower on August 8.
Chris Tracey, BEAR Scotland South East unit bridges manager, said: “Since the Queensferry Crossing opened in 2017 there have been three occasions when it was necessary to close the bridge to traffic until the risk of falling ice had passed. The last time this happened was in January 2021.
“Last winter there were no ice accretion events severe enough to close the bridge, so it was not possible to measure the impact of cleaning on site, however laboratory tests have indicated that cleaning does have a beneficial effect.”
Speed restrictions will be in place while the cleaning process is carried out, with limits dropped to a maximum of 50mph outwith peak times.
Last year, technicians abseiled from the bridge’s north tower to clean the cables by hand as part of a trial.
A remote jet washer has since been developed after research at the Jules Verne climatic wind tunnel in Nantes.
Mr Tracey added: “This year we will be using specially-developed winched cleaning shuttles using high pressure water to clean the cables, which were successfully trialled in November 2021.
“This will significantly shorten the time required to clean the cables and reduce the need for rope access.
“The ultimate test will be the next time an ice accretion event occurs on the bridge itself.”