Scotland's flagship road bridge is to be "cleaned" over the next three months in an effort to stop ice buildup from forcing it to close during the winter.
The £1.35bn Queensferry Crossing has shut three times since opening in 2017 due to accretions on the 288 metal cables supporting the structure.
The replacement for the Forth Road Bridge has been plagued by falling ice over the winter months.
A "considerable" amount of dirt and soil has built up on high-density polyethylene stay pipes that encase the cables.
Research conducted at the Jules Verne Climatic Wind Tunnel in France showed that cleaning these pipes could prevent wet snow from freezing and sticking to the material.
Work will begin on August 8 from the south tower to clean the pipes and is set to take around 12 weeks.
The speed limit on the bridge will be reduced to 50mph during the cleaning - except in peak traffic times.
READ MORE:Sensors again fail to stop danger to motorists from falling ice on Queensferry Crossing
Two new jet wash machines will be used to speed up the process.
Chris Tracey, BEAR Scotland southeast 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.
“In March 2021 it was noted that considerable dirt and soiling had built up on the HDPE pipes that encase the cables, and it was suggested that this may be helping ice to accrete.
“The cables on the north tower were cleaned last year by rope access using cloths and a mild detergent solution, however this method was slow and very weather dependant.
“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.
“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. The ultimate test will be the next time an ice accretion event occurs on the bridge itself.”
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