See https://en.wikipedia.org/wiki/Tram-train for a more extensive list of tram train solutions world wide.

Sheffield in the UK has tram trains - it was the first such implementation in the UK, and runs on national rail lines as part of the journey to Rotherham.

> while others, such as Cologne, have simply added platforms at their main stations to enable suburban trains to run through.

We did?

Cologne's tram system is weird. Over the last century, they merged the tram, subway and selected private railways into a single network. The result is sort of a tram network on steroids, that also runs underground and serves longer distances to two neighboring cities. But it's still separate from the national train network or even "real" suburban trains (S-Bahn).

(Edit: Just learned the term "interurban" for that...)

That's unlike Berlin or Vienna, where you sometimes have subway and S-Bahn side by side in the same station, but on different tracks. I think that's closer to what they mean with "through-running"?

> Tram-trains manage speeds about the same as the wholly tunneled Paris Metro.

Uhhh, it’s not.

E.g.

> Line 8 is 22.057 km (13.706 mi) long, including 2.8 km (1.7 mi) of open-air tracks in the southeastern suburbs.

https://en.m.wikipedia.org/wiki/Paris_M%C3%A9tro_Line_8

Maybe they just meant comparing it to the tunnelled sections but I also don’t see why that would really impact speeds. It’s the traffic/grade separation that gets you the speed advantage.

also the Paris Metro is kinda slow because of station density, so you may save a lot of walking but have a lot of station dwell time.

Go during the day and pick any two arbitrary points in Paris and you’ll usually find cycling faster than transit on Google Maps.

> This caps capacity and reliability.

Karlsruhe: The local operators have severe quality issues, in part due to this concept. There are like four points in the city where issues impact the whole network. The rolling stock is very bad compared to the other regional trains running in Baden-Württemberg (no/bad ac, flaky internet, no sockets, bad seating). The trains have way too little capacity, I’ve seen incidents, where they run three coaches (which they don’t do often, they are too long to enter the city), where people could not get in anymore. Some of the stations in the surrounding area are absolutely mental (Durmersheim for example), you have to walk over rails where ICEs and cargo goes through. Some trains are split or merged when leaving or entering the city, but it always causes delays. When trains can’t use the heavy metal rails and thus not leave the city due to ICEs getting priority, a lot of inner city traffic can be affected. The cooperation between the different infrastructure operators is also a source of problems.

Do not take Karlsruhe uncritically as an example where this model works well, yeah sure average numbers make it look good, but the reliability is complete ass. KVV always manages to surprise me on how bad it gets.

In Melbourne we loved our Tram Trams that run down the middle of the street and hold up the traffic. The W class trams were all fazed out and replaced with "light rail". Bigger Faster Better. Not. Melbourne has a good mix of tram and train - yes you take athe train to the city (a through route via the underground loop) and get on a tram for the last km. Small frequent trams are better for this and require lighter track. I think there was a recent HN article to this effect.

Time to reinvent the Interurban https://en.wikipedia.org/wiki/Interurban

Some combination of interurbans and golf cart cars and electric scooters and electric skateboards would make a marvelous urban transportation milieu.

London? London has 13 major railroad stations and they're all dead ends.[1] Crossrail, with expensive tunnels, now provides some east-west through services.

[1] https://en.m.wikipedia.org/wiki/File:Major_railway_stations_...

> A final model of light rail worth mentioning is interurbans. ...these systems were sometimes staggeringly expansive: at one point, it was possible to travel from Wisconsin to New York State exclusively by interurban.

I had no idea. A few systems are still in place: https://en.wikipedia.org/wiki/Interurban#United_States

> The low density of Charlotte means a transport network like Munich’s is not viable, but the city could take its pre-existing light rail network and join it up to the extensive network of railroad lines around the city that are currently used only for moving freight.

This is not a feasible option due to the vast difference in crashworthiness standards between US freight rail and other system types such as light rail. The FRA actually prohibits allowing these two types on the same network of tracks at the same time. However, they could use a line along the right-of-way were it big enough to accommodate another set of tracks.

Brussels is a great example of a train briefly turning into a subway. There's pretty much never a fare check either, so it's essentially a free north south subway line at very high frequency.