Untergrundbahn

Untergrundbahn is the German term for an underground railway, a rapid transit system in which passenger trains operate primarily in tunnels below ground. In everyday usage, the shortened form U-Bahn is common across German-speaking countries; Untergrundbahn is largely historical or formal, used to emphasize the underground aspect or found in older literature.

The system consists of grade-separated tracks, typically electric trains supplied by a third rail or overhead line, and stations designed for high-frequency service in urban centers. Most lines run underground in densely built areas and on surface or elevated tracks in suburban sections. Modern lines often employ safety features such as automatic signaling and, on some routes, platform-edge doors.

Historically, the idea of rapid transit through tunnels emerged in the 19th century, with early underground lines in several major cities. In German-speaking areas, Berlin opened what is now known as the U-Bahn in 1902, and the network expanded throughout the 20th century. The term Untergrundbahn was widely used in older texts, while U-Bahn became the standard name in contemporary usage.

Today, Berlin U-Bahn, Munich U-Bahn, and Vienna U-Bahn are the primary German-speaking networks. Each network combines underground, surface, and sometimes elevated sections and serves as an integral part of urban transportation, typically integrated with buses and trams and coordinated with regional rail services.