A few of Germany's largest cities have a full-fledged subway system, or U-Bahn.
For the most part, these systems are located underground, but may run on elevated tracks or at ground level, especially in outlying areas. These systems generally serve the central city and the immediate vicinity. Service is frequent, usually 5-15 minutes during off-peak periods. U-bahn lines are typically numbered with a "U" followed by a number.
U-Bahn stations in all German cities are marked with the standard "U" sign shown at the right above.