the first considerations of building a regional rail network in and around saarbrücken began in the 1990s. the bus service in central saarbrücken then ran at such a high density that the vehicles sometimes operated at one-minute intervals. following the example of the karlsruhe model, which had operated with great success since 1992, the saarland began to plan to build a regional stadtbahn. the core of the concept was the building of an inner-city railway line, while the outer branches would share the existing deutsche bahn railway infrastructure. as early as 1992, it borrowed a light rail vehicle from the karlsruhe stadtbahn and ran it on the fürstenhausen–gersweiler bahnhof–saarbrücken messebahnhof route on the rossel valley railway ("rosseltalbahn"), south of the saar.