From 1976 onwards, the Stadtbahn was integrated into the newly established Vienna U-Bahn system. For line U4, most of the stations of the Wiental and Donaukanal lines of the Stadtbahn were completely rebuilt. Platforms were raised to and current collection changed from overhead lines to third rail. While some of the station entrances at street level have been preserved, only Stadtpark station remains largely in its original form at platform level. New U-Bahn trains (class U), built by the Austrian manufacturer SGP, were introduced.