All the world loves a bridge that moves. Usually, the point of a bridge is that it is fixed – when so much trouble has been taken to overcome gravity and tame nature, instability is the last thing that you want – so there is surprise and delight when it confounds its own rigidity. I give you as an example Tower Bridge.
In an overlooked part of east London, weed-strewn and still industrial – a district un-steamrollered by the giant apartment blocks going up in much of the old docklands, close to where the River Lea joins the Thames – two curve-cornered squares of steel frame the view. They look like heavy metal sculptures. They are actually essential elements of the recently completed Cody Dock Rolling Bridge, designed by the architect Thomas Randall-Page and Tim Lucas of the engineers Price & Myers, which moves in a way that no bridge has done before. Its purpose is to make good a missing link in the Leaway, a “green corridor” that runs from Hertfordshire then along the Olympic park towards the Thames. It also serves as an emblem for the Gasworks Dock Partnership, a charitable social enterprise that has created a “community-based arts and creative industries quarter” on what was derelict land.
As its name says, the bridge rolls. It crosses a channel that runs from the Lea to an adjoining dock, and most of the time it provides a flat steel deck, level with the ground, which pedestrians and cyclists can use to get from one side to the other. When necessary, those squares can be turned through 180 degrees, such that the deck is raised in the air and turned upside down, which gives enough headroom for boats to pass underneath. It is operated by two manual winches, the tonnage of steel balanced in such a way that a bit of human muscle can shift it.
The simplicity of its idea requires fiendish mathematics and precise construction. The squares roll along sinuous tracks, kept in place by interlocking teeth and sockets, the angles and forces of each one different from its neighbour. Cake Industries, the company that built it, employed furniture-makers to construct the moulds for the concrete elements of the structure. It is, to be sure, a bit of a folly, definitely not the cheapest and easiest way of getting the job done. There’s something a bit Fitzcarraldo about the determination with which an eccentric idea has been pursued. But the finished object gives, as Randall-Page puts it, “childlike joy”.
Meanwhile, in a gentler place some distance up the Thames, another structure has been completed that is also in the nice-to-have rather than must-have category. It is a bridge under a bridge, a way of getting a riverside path to pass below the Victorian iron arches of Barnes Railway Bridge. Previously, users had to trek inland, through a menacing tunnel under the tracks, and back again to the riverbank. Now they can travel over a broad, winding deck, falling then rising again, that projects over the water with a mild frisson of peril.
Dukes Meadows Footbridge is designed by Moxon Architects, a practice based in London and Aberdeenshire with several other bridges to its name, and the structural engineers COWI. This, too, has required ingenuity, albeit less for the self-imposed reasons at Cody Dock: the deck has to just clear the high-water mark of the tidal river, while giving enough room beneath the arches, without obstructing access for maintenance for the old structure. It could impact neither on the many rowers who use this stretch (the Oxford and Cambridge boat race finishes nearby), nor on the endangered snails in a neighbouring nature reserve, which meant that its route and its lighting were designed not to disturb them. Its main span, manufactured in Essex, had to be floated upriver in one piece and installed in a brief window of time when the tide was sufficiently high.
The result is faceted and intriguing, its irregularity driven by the imaginative response to circumstance. “It’s marvellous,” says an elderly user, unsolicited. Funded by the London borough of Hounslow and the mayor of London’s Liveable Neighbourhoods scheme, it makes a striking contrast with the years-long, still-ongoing struggle to make Hammersmith Bridge, the next crossing downriver, safe for traffic. It’s easier, evidently, to build one that doesn’t actually cross a river than to repair one that does.
Moxon is also working on a plan, long promoted by local citizens, to make a disused part of the old railway structure into a linear park – a small version of New York’s High Line, or a successful version of Boris Johnson’s doomed Garden Bridge. Like the new footbridge, this project is shaped more by quality-of-life considerations than the hard industrial imperatives that drove either the original railway bridge or the big old structures of docklands.
Modern architects and engineers build on the 19th-century legacy of Isambard Kingdom Brunel and Thomas Telford, but to different ends – you wouldn’t have caught them worrying so much about snails. You could call the bridges at Cody Dock and Dukes Meadow elegiac engineering, conscious of their forebears, and more sensitive, if less world-changing, than them. When it comes to the wellbeing of cities, they also serve.
