The Ringzug (“ring train”), also called the 3er-Ringzug (“ring train of the 3”) is a passenger transport network in the districts of Tuttlingen, Rottweil and Schwarzwald-Baar in southern Baden-Württemberg, Germany. The Ringzug went into regular operations on 31 August 2003 and has operated in its current form since 12 December 2004. The concept of the Ringzug is the operation of a clockface timetable, coordinated with a variety of other buses and train services, over an S-Bahn-like network in a rural environment. In March 2006, the passenger association Pro Bahn described the Ringzug as an exemplary public transport system at its 2006 passenger transport awards (Fahrgastpreis 2006). The Ringzug has aroused interest beyond the region and can point to steadily rising passenger numbers and declining deficits.
The term Ringzug was chosen because its route was originally intended to form a ring, but it is interrupted by the gap between Immendingen and Donaueschingen. The network also includes lines that are not part of the ring. These include the Trossingen Railway and parts of the Breg Valley Railway, the Wutach Valley Railway and Danube Valley Railway. The alternative term 3er-Ringzug indicates that three districts participate in the project.
The majority of stations in the Ringzug area were skipped in the 1970s and 1980s due to the implementation of Deutsche Bundesbahn's so-called eilzugmäßigen (semi-fast running) of regional services. On the 28 kilometre-long section of the Stuttgart–Hattingen railway (Gäubahn) between Tuttlingen and Rottweil, Spaichingen was the only remaining stop. No train stopped even in Aldingen, which had 7,500 residents.