Monorail

An urban rail transit mode in which trains run on or hang from a single rail or beam instead of a conventional two-rail track. Most modern systems use the straddle-beam design descended from the 1950s ALWEG system, in which rubber-tired cars ride atop a concrete or steel beam for traction and stability, while a rarer suspended form hangs the cars beneath the guideway; the Wuppertal Schwebebahn in Germany, opened in 1901, is the oldest such system still running. Because it is grade-separated by design, a monorail avoids street-level traffic conflicts and offers passenger capacity between a tram and a full metro line. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/