This means running a railway line through the city often doubles or triples the number of trains it can handle. This caused great inconvenience to passengers, who had to change to the city’s tram network in order to get to the old center. Karlsruhe’s inventive step, which came later, was to extend the tram-train onto railway lines that did not just carry tram traffic. In many cities, the suburban railway lines have already been built: they just need linking up to a tram network. In smaller cities like Tours, this could be done by running trains onto the existing tram networks.