The A81 is an important European north-south connection. It completely crosses the state of Baden-Württemberg and connects the cities of Würzburg, Heilbronn and Stuttgart with the area around Lake Constance. As a long distance road, the A81 functions as a national connecting road and complies with the road category A I according to the German guidelines RAS-N.

The section being planned lies south of Stuttgart near the cities of Böblingen and Sindelfingen. The extension runs through a heavily built-up and extremely flat area.

A 50cm-wide strip beyond the hard shoulder was developed to serve as a channel for the central reservation drainage. By reducing the binder course, a maximum channel depth of 5cm can be achieved while maintaining the thickness of the covering layer. The water collected in the channel then flows into the drainage system under the central reservation via outlets.

The card_1 Cross-Section designer has proven itself to be an extremely flexible and efficient means to minimise time, energy and costs. By running iterative calculations of the accumulated surface water, the resulting water level width in the channel is calculated and displayed for each cross-section, showing the expected spacing of gullies.

The results of the final evaluation regarding the planning and effectiveness of the drainage system were presented to the regional council of Stuttgart using the card_1 Route Simulation.