Hoenheim, a forgettable sprawl of pastel houses, allotments and garages, is where Strasbourg peters out into the flat Alsatian countryside and where tram line B ends. It is also the location of one of the most intriguing-sounding pieces of architectural commissioning in the recent past: a park-and-ride station by avant-garde architect Zaha Hadid.
The station and surrounding car park are utterly deserted this bright Monday morning, save for two distant black-clad figures. One, half concealed by a cape, is crouching behind a tripod, while the other sweeps the vast expanse of black tarmac with a caretaker's broom. The figures turn out to be the celebrated architectural photographer Hélène Binet and project architect Stephane Hof and he's thoughtfully tidying up the foreground while she directs him from beneath the hood of her large-format camera.
Binet pops her head out from beneath her cape to say hello and agree that, yes, transport strikes create ideal conditions for photographing station car parks. Hof drops his broom and offers to explain the project over coffee. Minutes later we are sipping black espresso from plastic cups in a fortified site hut ("It's a really bad area; they burn 1000 cars a year") and discussing how this remarkable project came about.
Back in 1998, the city of Strasbourg decided to commission a series of artistic "interventions" to embellish the new tram route, being built as part of a concerted effort to keep cars out of the historic city centre. Hadid, whose work straddles the boundaries between architecture and art, was asked to design a transport node at which commuters could leave their cars for the day and go to work by bus or tram.
Hadid interpreted this constant flow of people and vehicles literally, basing her design concept on a series of overlapping forces and trajectories. "It's a response to the site and the idea of movement," says Hof.
The 700-space car park, which occupies two former football fields separated by an access road, is laid out like a magnetic field, each row of white-lined bays shifting in orientation by one degree as if the mass of the station has caused a warping of the ground around it.
The effect of this simple distortion on something as mundane as a car park is quite extraordinary; the sweep of converging lines is both disorientating and delightful and today, unsullied by vehicles, it has the ethereal quality of a crop circle.
The station itself takes the trajectories of trams and buses as its starting point. The concrete and steel canopy is an interpretation of how these parallel vectors – and the distorting effect of the surrounding car park upon them – might look if they could be captured and recorded in three dimensions.
Again, the thought that has gone into the normally humdrum relationship between a structure (the station) and the surrounding landscape (the car park) is immediately striking; cut-out slots in the station roof cast strips of sunlight on the ground that echo the trajectories of the parking bays, and the line of the canopy roof is picked up by a curving strip of concrete that sweeps across the tarmac apron. The two elements fit together as harmoniously as a barn in a cornfield.
Structurally, the station consists of a single plane of concrete that starts at ground level and then folds up and over the platforms, reaching a height of 7.5 m. It is supported by 55 columns of seemingly random placement, thickness and inclination. The conceptual simplicity of the canopy belies the complexity of its execution: the wooden shuttering was designed to leave a seemingly skewed pattern in the folded concrete that, were it to be straightened out, would form perfectly straight lines.
The entire 3000 m2 roof slab was cast in one piece in a day, with concrete crews pouring the first 100 mm layer at 4am, adding two more layers to reach the required thickness of 300 mm.
The random placement of the columns caused an engineering headache, says Hof, as they created unsupported spans of up to 25 m in places and are not all necessarily where structural logic would have them. As a result, some of them actually work in traction, holding the roof down and giving it what Hof calls "seismic stability".
Despite the reputation the French have for enlightened procurement, this particular petit projet has not been plain sailing. As a result of local political shenanigans, funding for the £6m project was temporarily cut off late last year, meaning a series of final flourishes, including a bike rack suspended from the canopy and an angular concrete toilet, have not yet been constructed ("there's still this much to build", says Hof disconsolately, indicating a two-inch wodge of drawings on the table).
Most dramatically, each bay in the car park will eventually be furnished with an inclined light post. These will form rows, each slightly higher than the last, that will give drivers the impression they are entering a 3D force-field.
The Strasbourgeois will have to wait a few more months for this further embellishment to their daily commute – but then, Hadid has already given them enough to think about for the time being.
