Testfeld Reallabor Radbahn

Radbahn is a project born in 2014 and proposed to the city of Berlin by the association “Paper Planes”. The idea is to reuse the space under the U1 viaduct, the oldest underground line that runs 9 km through the city, as a space dedicated to slow mobility. In 2022 fabulism, in collaboration with Nuko, won the tender for the design of the first 200 m test section.

The Testfeld Reallabor Radbahn project is located in the historically mixed and vibrant district of Kreuzberg, along Skalitzer Straße, connecting the Kottbusser Tor and Görlitzer Park intersections. Formerly used as a car park, the site is now being transformed into a new urban green space open to the city. The project regenerates the vacant space under the viaduct as a hybrid place where slow mobility and nature can return to a new public space, or rather a covered linear park.

The design is largely based on the results of a participatory process. The “islands” idea, developed during the online workshops, is based on the assumption that different users and functions will take place along the cycle path. Activities such as sitting, playing or events will take place on the “Interaktionsinsel”. The second island, called the “Radinsel”, is designed mainly for cyclists, with small infrastructures and tailor-made objects. Between the two islands, the central strip will be transformed into a green linear park, with several biodiverse plantings on the sides, which will accompany cyclists along their route in a pleasant way, enhancing the experience of nature in the city.

Several design strategies are applied in the project:

1) Demineralisation: The surfaces of the car parks are transformed into permeable areas, open to the colonisation of plants.

2) Reuse of materials: The reddish concrete paving that covered the former parking niches provided a valuable resource for the redesign of the project. The concrete blocks from the car parks were reused to create the permeable surfaces of the islands, while the kerbs were used as paths through the vegetation.

3) Water as a resource: The green strip is designed as a climate-adapted space. The planted areas are slightly modulated in order to collect and retain rainwater during heavy rains, to promote slow evaporation and to allow the natural development of trees during dry periods. In addition, a phyto-purification system (designed in collaboration with the Technical University of Berlin) has been installed to test the quality of the water coming from the viaduct.

4) More than 4000 plants: the green area is designed in a multifactorial way, where different characteristics allow the creation of a mosaic of situations that adapt and test multiple conditions. The soil is treated in 8 different ways, ranging from complete removal of the existing soil to partial maintenance and experimentation with different substrates and treatments. The diversity of soils is matched by the diversity of vegetation: 4,000 plants are planted according to many factors: exposure to the sun, water permeability, pollution, proximity to roads and paved areas, animals present in the area; this makes the space and the greenery a true testing ground for biodiversity.

5) Smart infrastructure: A large collection of objects has been specially designed to create an interactive and inclusive public space. These include newly designed benches and sound objects for the little ones, a spacious wooden tribune where visitors can relax, a repair station and a specially designed inclined litter bin for cyclists.