A tram-train is a type of light rail vehicle that meets the standards of a light rail system (usually an urban street running tramway), but which also meets national mainline standards permitting operation alongside mainline trains. This allows services that can utilise both existing urban light rail systems and mainline railway networks and stations. It combines the urban accessibility of a tram or light rail with a mainline train's greater speed in the suburbs.[1]

The modern tram-train concept was pioneered by the German city of Karlsruhe in the late 1980s,[2] resulting in the creation of the Karlsruhe Stadtbahn. This concept is often referred to as the Karlsruhe model,[1] and it has since been adopted in other cities such as Mulhouse in France[1] and in Kassel, Nordhausen and Saarbrücken in Germany.