This is a more nuanced summary than you often see; honestly tram trains have always seemed like an extremely overhyped solution, only one step down from out-and-out gadgetbahns. Yes there are a handful of cities in which they apparently work ok. But they're far from the magic bullet certain kinds of transport fan want to portray them as. Often what your city needs is just a regular tram, or a regular train, or maybe even just integrated ticketing so that people can easily change from the train to the bus.