The crossing comprises a 290 m long immersed tunnel section constructed of three elements of rectangular cross section for dual railway tracks and a service gallery in separate bores. The immersed tunnel is installed above the seabed on discrete foundations with bearings. At the Riddarholmen site a 100 m long cut and cover tunnel connects the rock tunnel under Riddarholmen with the north end of the immersed tunnel. At the Söder Mälarstrand site the immersed tunnel is connected directly to the rock tunnel via a short 20 m long cut and cover tunnel.
Ramboll provided the design tender design for the contractor. The design included the design of the whole immersed tunnel, the cut and cover tunnel, the rock tunnel under Riddarholmen, the connections between the tunnels, as well as the open excavations connected to the project. In addition, Ramboll is also providing the necessary services for the design of the temporary works at the site.