i’ve always wondered this

lightrail, streetcars, trams. Why must they be built to be incompatible with heavy rail? why can’t heavy rail be built with a bunch of level crossings, street level stations, slow speeds, and function exactly the same as light rail?

if compatible, the rail could act heavy at designated tracks and light at others, removing what would otherwise be an interchange. it would also allow the light rail to have a higher top speed at express areas.

what am i missing?

  • Tuukka R@piefed.eeEnglish
    13·
    3 days ago

    Basically because it’s light.

    For example in Karlsruhe, Germany, they do have a system where you enter what is essentially a metro station (a.k.a. “a subway station”). You then enter a train that leaves the tunnel after a couple of stations and starts turning in the intersections above the ground and stopping in traffic lights. After passing the central railway station, it enters the railway tracks and proceeds to run the next 40 minutes along the very same railway tracks used by cargo trains and high speed trains.

    So yeah, that can be done and is being done. But it is a very complex thing to do!
    By far the most important difficulty is that the tram is too light to be safe on the railway tracks just like that. If there is a collision between a train and a tram, the heavy train will absolutely obliterate the tram. There won’t be any survivors in the tram if that ever happens. This means, you need to clear a very long stretch of the track of any heavy trains whenever a tram is about to use it. This decreases the capacity. A tram also cannot be reasonably made to run 160 km/h like passenger trains usually do, and speed differences between trains are a horror for the railway’s capacity.

    At the same time, the tram’s ground clearance must be higher than usual for trams, which requires higher platforms, which can be cumbersome to organize in city streets. It also easily means that handicapped people have it more difficult entering the tram.

    If you want to make the trams crashworthy enough to have a fighting chance against a train in a collision, you will end up having such heavy trams that they cannot be used on city streets.

    There are situations where it really does make sense to run trams on railway tracks, but in most cases it’s better to choose one or another instead of trying to combine a tram and a train into one thing. But, Karlsruhe has a good example of when this combination does make sense!

    Here’s a Youtube video of a ride on a metro->tram->train vehicle :)
    A high-speed train is encountered at 35:26 and a cargo train at 38:48.