>>1033926>But it is not without its flaws. It requires trains that can run on different voltages as well as transfer stations at the city borders. Gauges need to be compatible or you need triple tracks everywhere. Kassel does the reverse where regional trains now serve tram stops in the city center, but a third rail had to be build for those since the trams do not use standard gauge.However, all of these issues disappear when talking about completely new lines, or lines rebuilt from abandoned train ROWs. To me, that's more interesting than the Karslruhe-type system. It would allow a cheap tram and commuter train hybrid, very useful for places where demand isn't enough to fully warrant either a tram or a commuter train.
There used to be an interesting project for the city of Manresa, about an hour and a half from Barcelona, where the idea was to use two rail branches which are only used for freight trains to and from potassium mines. These branches are metre gauge and not electrified. In fact they're part of a metre gauge commuter system independent of the mainline railways, but passenger service was discontinued in the 1970's (when the upper portion of the line was also closed).
The idea was to build a tram-train so that the trams could run into the towns reached by these branch lines, which now end outside where the potassium mines are. On the other hand, the line would also be extended into Manresa itself, possibly reaching the mainline station which offers much more convenient service to Barcelona. The narrow gauge rail line used to run through the city of Manresa all the way to the mainline station, for freight to be transferred, but this line was also closed in the 60's or 70's. A tram line could be built basically running along the former ROW with some single-track stretches (Manresa is a very cluttered city with many hills and narrow streets, so there's no big avenues to easily lay down a tram line).
