High design speeds lead to rigid trajectory elements on both the road and the railway. Topographical obstacles can often only be overcome with bridges or tunnels. Tunnel constructions are in the same mass connecting elements as bridges.

Environmental requirements and limited space in the urban agglomerations are further factors for the realization of underground transportation infrastructure.

Underground traffic structures allow many cross-sectional shapes and dimensions. An optimal design can only be achieved if the future use is defined early and unambiguously. The cavity to be created must be optimally built around the future traffic facility. The operational aspects must be taken into account from the outset.