A few points I want to add: The Stadtbahn (called Tram-Metro in this Article) is usually just as fast in the outlying areas as in the inner areas and rarely street running, just doing it with less infrastructure. It's just that rail tracks are even faster.
There are quite a few newly built S-Bahn Tunnels in cities under a Million in Germany, in Frankfurt, Stuttgart and Leipzig (you could quibble about citie vs metro area population).
The major downside of Tram-Trains compared to S-Bahns, Rapid Transit or just through running away from the city center is that they slow way down in the city center, much more than the other options. This makes it a bad fit for the sprawly, north american cities without a strong center which have much more demand for non city center destinations and a much more expansive center compared to european cities with tram-trains.
The big benefit of Tram-Trains is the flexibility. Over a region, some sections can implement their own new through running section for the Network (Heilbronn), be almost a metro (the Kombilösung and some parts of S11) or provide S-Bahn style service (e.g. Freudenstadt for a mediocre Regio S-Bahn).
But it's a master of none: Too slow and cramped for high-quality regional services, too few doors for rapid passenger exchange, too demanding and expensive (electrification and vehicles) for connecting small rural lines, legally limited in capacity (75m) for very busy services.
They can be great, but it really depends on local circumstances.
Before converting commuter rail to Tram-Trains, most American cities should first implement a frequent (at least 2tph), all-day, regular service with more urban stations for commuter rail and perform true ticket integration between mainline rail and their other urban transport (the ticket integration is very important!). This also applies to many european cities, such as in France, Spain, Belgium, ... .
A few points I want to add: The Stadtbahn (called Tram-Metro in this Article) is usually just as fast in the outlying areas as in the inner areas and rarely street running, just doing it with less infrastructure. It's just that rail tracks are even faster.
There are quite a few newly built S-Bahn Tunnels in cities under a Million in Germany, in Frankfurt, Stuttgart and Leipzig (you could quibble about citie vs metro area population).
The major downside of Tram-Trains compared to S-Bahns, Rapid Transit or just through running away from the city center is that they slow way down in the city center, much more than the other options. This makes it a bad fit for the sprawly, north american cities without a strong center which have much more demand for non city center destinations and a much more expansive center compared to european cities with tram-trains.
The big benefit of Tram-Trains is the flexibility. Over a region, some sections can implement their own new through running section for the Network (Heilbronn), be almost a metro (the Kombilösung and some parts of S11) or provide S-Bahn style service (e.g. Freudenstadt for a mediocre Regio S-Bahn).
But it's a master of none: Too slow and cramped for high-quality regional services, too few doors for rapid passenger exchange, too demanding and expensive (electrification and vehicles) for connecting small rural lines, legally limited in capacity (75m) for very busy services.
They can be great, but it really depends on local circumstances.
Before converting commuter rail to Tram-Trains, most American cities should first implement a frequent (at least 2tph), all-day, regular service with more urban stations for commuter rail and perform true ticket integration between mainline rail and their other urban transport (the ticket integration is very important!). This also applies to many european cities, such as in France, Spain, Belgium, ... .