As Light as Air
The world’s largest air-supported membrane cushion dominates the newly designed forecourt of the train station in Aarau
People who exit the train station should immediately realize they are in Aarau. The spacious, open and urban station forecourt is a pleasant and bright place for all, structured by islands of light and unique materials. Like a clearing in the woods, the diaphanous air cushion roof, which is open at its center, spans over the forecourt. It protects the passing travelers beneath, but is airy enough that the waiting area does not seem like an enclosed hall.
Zurich, February 2014
As the central public transport hub for the entire region, the train station in Aarau serves as a point of departure, arrival and transfer for more than 40,000 train and bus travelers every day. Due to assorted small structures, street furniture, art objects and planters that had gathered over time, the station forecourt was barely still perceived as a public open space. Bahnhofstrasse, the street leading to the train station, was a spatially defining axis dominated by car traffic, thus cutting the space off from the surroundings. That is why a new station forecourt with a bus terminal and optimized public access was also envisaged along with construction of the new train station. After lengthy preparatory work in close dialogue with various interest groups, the Aarau populace approved the project with an overwhelming majority in 2009.
Tidying Up Traffic
A central bus station on the forecourt now concentrates all the buses to the south of Bahnhofstrasse. As a result, it was possible to reconfigure the traffic situation in the immediate environs. The most striking change is the relocation of the access ramp for the train station’s parking garage. Now that it has been moved to Poststrasse, it no longer cuts through the square in front of the station, thus enabling a spacious and orderly urban space.
Together with the Aarau general planner suisseplan AG, the Zurich architecture firm of Vehovar & Jauslin has drawn up a project that essentially consists of four areas: the underground Einstein Passage, the adjacent Hächler Hall, the train station forecourt and the bus station with its impressive canopy.
Einstein Passage
The formerly unattractive and poorly illuminated pedestrian underpass was an important connection between the train station, on the one side, and the city center and the cantonal school on the other. Fresh materials and new uses ensure that the tunnel feels safe and comfortable for the numerous commuters and passers-by, despite insufficient daylight.
The highlight of the new Einstein Passage is surely the interactive light installation Gravity, which the architects developed together with lighting designer Rolf Derrer. The underpass is illuminated by continually changing colorful letters and multilayered patterns. Special sensors register the movements of the pedestrians, enabling the light show to change, depending on the season, weather and time of day, thanks to artificial intelligence. So this functional passageway becomes a poetic, traversable film that presents a new and surprising appearance every time as it accompanies the passers-by on their way.
Hächler Hall
Until now, the underground hall was a rather unfriendly and dismal space that people preferably avoided. The wall relief, created by the well-known artist Peter Hächler in the 1970s, could no longer hold its own as an artwork in the run-down surroundings.
The restoration carried out within the existing spatial proportions transformed the hall into a pleasant passageway and space to linger. Pairs of new columns, which were structurally necessary, form gondola-like benches that are clad in warm red. Neutral colors and a light-colored floor frame the expertly refurbished relief. General planner Markus Goldenberger from suisseplan explains that emphasis was placed on creating a high-quality impression despite using affordable materials. The closely spaced round light fixtures also bestow the space with more the character of a lobby than that of an underpass.
The Station Forecourt
As part of the reorganization, the forecourt of the train station was completely redeveloped. The result is an orderly, open square with a bus station at its center. The buildings that were once relegated to the periphery, and the train station itself, now have a new address on the station forecourt. And Hotel Aarauerhof is right in the midst of it. In this way, two compartmentalized areas are now joined to form the largest square in Aarau – an urban outdoor space that, because its area has nearly doubled in size, is now commensurate to its significance within the city.
The paving is as uniform and accessible as possible in order to fulfill the diverse requirements for a well-maintained and friendly station square. In this way, the forecourt becomes a single entity and also succeeds in integrating Bahnhofstrasse as part of the square.
The necessary furnishings with seating elements and garbage cans take the form of small islands in the space, which are highlighted at night with energy-saving LED lighting. The relaxed appearance prevents the now tidy place from immediately becoming cluttered again. The red, tulip-shaped seating elements are like refreshing bouquets of flowers that confer a feeling of spring even in cold and wet weather. As a result, the station forecourt invites you to linger and pause, acting as an urban counterpart to the cantonal school park.
Bus Station with an Impressive Roof
The image of the new station forecourt is unquestionably defined by the roof over the actual bus terminal, a canopy that the locals already affectionately call the “cloud.” Its organic shape with a clear view to the sky at its center originates from the desire to not place an upper limit on the square, but to welcome travelers in a friendly and bright environment. “From the beginning, we wanted to create a spatial atmosphere under the roof that resembles a clearing in the woods. “In order to greet the passengers in a bright and friendly environment, a very light, diaphanous material was selected,” explains architect Mateja Vehovar.
We chose an air-supported membrane cushion made of the synthetic material ETFE. Such membrane roofs are not only easily designed in various forms, but are also extremely light, durable, weather-resistant and self-cleaning. The expansive cushion is held up from within by a freeform steel construction. An irregular network of steel cables across the outer surfaces gives form to the air cushion. The necessary utility lines for drainage, lighting, recirculating air and measurement technology run invisibly inside the construction. Thus the roof appears light and airy instead of looking like a technical installation. For all the materials used, we paid attention to the issue of sustainability. This also holds true for the air recirculation system. “Thanks to the excellent air tight quality of the cushion construction, the task of the ventilation system is nearly limited to solely adjusting the air pressure in the roof to suit the changing weather conditions,” explains Gerd Schmid from the Radolfzell engineering firm formTL, which was responsible for the structural and technical design of the roof.
“Since it’s often foggy in the Central Plateau, the blue coloring of the upper membrane is meant to ensure that a bit of blue sky always floats above the buses,” says Vehovar. For the blue upper and clear lower membranes, the architects and designer Paolo Monaco together expressly developed slightly differing, seamless printed patterns. Their appearance, which is reminiscent of foam bubbles, makes it possible to allow the structure of the entire roof to be read from below and, at the same time, to provide shade and prevent the unwanted emission of direct artificial light into the night sky.
The roof exudes lightness and joy. Perhaps also because it responds so naturally to the light of the surroundings: Whether through the play of light and shadow, through the light reflections of its own lighting and the sun, or because passing clouds cast fleeting images upon the roof.
The world’s largest membrane air cushion represents a unique mixture of functional, advanced technology and a varied, delightful play with people’s sensory perception. It is more than just a mere bus terminal, it is functional art in urban space – a landmark for Aarau.

Client
Bus Station Roof: City of Aarau, Municipal Building Department
Train Station Forecourt: City of Aarau, Municipal Building Department;
Canton of Aargau, Department of Construction Traffic and Environment;
Swiss Federal Railways SBB;
Aare Parking AG, Aarau

Planning Team
Architecture: Vehovar & Jauslin Architektur AG, Zurich (CH); Mateja Vehovar, Stefan Jauslin
General Planning, Civil Engineering: suisseplan Ingenieure AG, Aarau (CH); Markus Goldenberger, Jürg Egli, Felix Wälty
Structural Engineering for Roof: formTL ingenieure für tragwerk und leichtbau GmbH, Radolfzell (DE); Gerd Schmid, Manuel Neidhart, Vitali Melzer, Sven Haag
Lighting Design: Atelier Derrer, Zurich (CH); Rolf Derrer, Stefan Keller
Pattern Design: Vehovar & Jauslin Architektur AG, Zurich (CH) in collaboration with Paolo Monaco, visual designer, Zurich (CH)
Electrical Engineering: HEFTI. HESS. MARTIGNONI. Aarau AG, Aarau (CH); Adrian Bühler, Phillip Woodtli, Marco Andrist
Wind Tunnel Testing: Wacker Ingenieure, Birkenfeld (DE)
Contractors
Joint Venture for Roof
Steel Construction: Ruch AG, Altdorf (CH)
Membrane Construction: Vector Foiltec GmbH, Bremen (DE)
Support Air System: ELNIC GmbH, Rosenheim (DE)
Printing: Reisewitz Beschichtungsgesellschaft mbH, Penig (DE)
Station Forecourt
Civil Works: Implenia Schweiz AG, Baden (CH)
Metal Construction: BURRI public elements AG, Glattbrugg (CH)
Hunkeler + Hediger Metallbau AG, Oberentfelden (CH)
Seating: Tulpi BV, Nieuwegein (NL)
out-sider a/s, Copenhagen (DK)
Electrical Works: IBAarau Elektro AG, Aarau (CH)