Reference: A4 Tunnel Cholfirst SiSto

The A4 motorway between Flurlingen and the border was opened in 1996. Part of this section, south of the Rhine, is the three-lane Cholfirst Tunnel. The tunnel is 1260m long and operates with two-way traffic. The tunnel features longitudinal ventilation with jet fans. To improve tunnel safety, a parallel egress tunnel (SiSto) was constructed. The egress tunnel runs parallel to the main tunnel at a distance of 40m and is connected by six cross passages.

The egress tunnel has a pressurisation system consisting of axial fans at each portal. The fans are installed parallel to an airlock. In normal operation, the ventilation of the safety tunnel maintains a moderate positive pressure relative to the road tunnel. In an emergency, even with all six emergency exit doors open simultaneously, a minimum airflow velocity of 1m/s is maintained in each door.

Supply Fan, Ventilation Station Rhein

South Portal Structure