The Queensferry Crossing, the UK’s tallest bridge and one of the most monitored in the world, has a secret feature that few people know about: a monorail shuttle that runs inside the bridge deck for maintenance purposes.
The Scotsman was given an exclusive tour inside the £1.35 billion structure by bridge managers BEAR Scotland, who revealed how the shuttle, nicknamed “The Rat”, and other hidden facilities make the crossing easier and safer to maintain than its adjacent sister, the Forth Road Bridge.
The Rat: A fast and convenient way to access the bridge
The monorail shuttle, which can carry two people and small hand tools, travels along a tunnel under the carriageways, passing close to the three towers of the bridge. It can reach speeds of up to 8.5mph, allowing staff to get to work sites quickly and work for longer.
Chris Tracey, BEAR Scotland’s south east unit bridges manager, said: “It’s mainly used for inspections, so the principal advantage is time – we can get to a work site quicker and work for longer, otherwise staff would have to stop earlier to walk back at the end of a shift. It is also safer, there’s no question about it. Anything that improves access is beneficial.”
Gantry cranes: A multi-level platform for inspecting the bridge
Another feature that makes the Queensferry Crossing stand out from other bridges is its six gantry cranes that run on monorails suspended under the deck. These cranes can cover different sections of the bridge, such as for inspecting the underside and sides of the deck. They can carry up to 20 people and operate in winds of up to 35mph.
The gantry cranes also provide a different perspective of the bridge, which appears flat from a distance but has a noticeable camber along the underneath of the deck.
Maintenance hub: A complex of offices and workshops at the south abutment
The south abutment of the bridge, where it meets the land, houses a complex of offices and workshops that serve as the bridge’s maintenance hub. It is also where some 2,200 sensors continuously check aspects of the bridge, making it one of the most monitored in the world.
The complex has space for vehicles to drive in and is among the only interiors of the bridge where traffic can be heard as intermittent thuds as vehicles pass over the expansion joints above.
Tower lifts: A larger and smoother way to reach the top
The Queensferry Crossing also provides easier access inside its towers than its adjacent sister, with larger lifts that can accommodate up to four people while only two can comfortably fit in those of the latter. They climb the equivalent of some 40 floors to reach the tops of the towers, which range from 663ft (202m) to 689ft (210m) above the water.
The centre tower is Scotland’s tallest free-standing structure, dwarfing the Forth Road Bridge, 164ft (50m) below. The Queensferry Crossing was also the world’s longest three-tower, cable stayed bridge when it opened six years ago.
Ice problem: A challenge that may prove impossible to solve
Despite its advanced design and features, the Queensferry Crossing still faces some challenges that may not have easy solutions. One of them is the problem of ice forming on and then falling from the bridge’s cables, which has closed the crossing three times, the last one in 2021.
Mr Tracey said: “We have found it will be very difficult, if not impossible, to prevent ice accreting. Since we cleaned the cables, we haven’t had an ‘event’. But it’s too early to say that that’s the reason – it may just be the climate over the last couple of years has not been conducive to ice forming in such a way that would cause damage to vehicles.”
He said monitoring and weather forecasting had predicted ice formation “pretty accurately”, while newly-installed automated barriers would enable traffic to be switched to the Forth Road Bridge within half an hour once they were fully operational, should the crossing have to close again.
