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Commuter rail/S-bahn grade-seperated crossings

Started by noahclem, November 15, 2020, 10:40:51 AM

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Hello all,

I've been wrestling with this scenario for a while and struggle to find a conclusion I have any reasonable degree of comfort with: when is it advisable/realistic for commuter rail type systems to require grade separation when crossing each other, particularly in areas closest to a central station? I've tried to base it off RL systems but differences in city size, type of commuter rail system, number of lines branching off, and whether hub station is a terminus or pass-through, confuse things to the extent I seem to work away with more questions than answers.

If I were to get a bit more specific about the question at hand I'd describe it as a terminal station in a metro area or 0.6-1.1M people with its nearby traffic split three ways ~2km to the east, and with non-commuter/longer distance rail traffic also split very roughly three ways. The 3 main branches all later diverge into at least 2 separate branches each but the number of the most heavily trafficked lines is more limited than that.

Thanks and good luck with whatever projects you have going :)


Sydney's Central Railway Station is a good example. It is both a Terminus for suburban and country trains as well as a through station for the eastern suburbs (largely underground) and city circle (underground) lines. Also, Sydney is a hilly city and there are lots of natural grade changes anyway.

In this google maps link
You can see a lot of grade changes and crossing lines adjacent to the park area (next to the blue tennis courts)

Other examples must go to the great rail makers themselves: the Brits.
Look at any large station in London - Euston,  st pancras  and Kings cross: three terminals almost adjacent to each other - and you will see countless viaducts and crossing separations leading in and out of these stations. The reason for the English versions is historic: many of the lines were initially privately built and thus, didn't interact with competitors lines (the size of the rail gauges). Of course, now, everything is the same gauge but a legacy of this is the grade change crossings.


Wow, that's quite the crossover system just south of Central! Kinda funny how little attention I pay to Sydney relative to Melbourne, long an inspiration for both trams and same kind of s-bahn-esque, quasi-metro rail network I keep mentioning.

I've been reconnoitering fun areas like that around Clapham Junction, Hamburg Hauptbahnhoff, and Oslo Central trying to make sense of all the crossings, when to use 4-track rail, 2-track rail, single or a wider variant, and attempting to apply the lessons to a smaller scale city. For as long as I've made serious efforts at realistic cities I've inevitably kept expanding the size and scope (generally in order to justify excessive freeway networks and other transport) of those cities; this time I'm trying to set a very firm upper limit at approximately a million metro area and hoping to substitute idiosyncrasy for excessive redundancy and disciplined realism focused on mass transit for the old super-interchanges (me being me there will still be super-interchanges :D but lane counts will be down, interchanges more autobahn than Texas-Toronto-traffic-tantrum, non-motorway arterials more common, etc.

A weird quality of rail mass transit around this size of planned city is it seems to rapidly increase or decrease in importance and complexity and ridership, on average, within the space of a couple hundred thousand peeps, suggesting there might be some kind of "critical mass" point around there (of course dependent on a city's geography, alternate transport options, etc) that affords the scale and service frequency sufficient to create a positive feedback loop of increased ridership. My hope is to replicate a system on the relatively small end of size yet big enough to feature some of the overpasses and stations and complexity I always enjoy--but firmly avoid my usual size inflation. 

This is a rough version of my rail plan (rgb topo map with sea dark blue and pink squares size of large city tiles) with terminal central station near center and black representing commuter and intercity rail. The light red represents hypothetical metro/U-bahn/light rail service. In addition to and adjacent to the branching lines east from central I plan a series of railyards and depots, effectively constituting a 4th branch in some sense.

Closest probable example is G´┐Żorg, albeit with less commuter/T-bahn relative to longer distance

Helsinki is another main inspiration
It's a bit of a weird case in that there's not many branches and that the metro, running primarily east-west from central station and south of the commuter railways, functions very similarly to the commuter rail network.

Where and whether to include grade-separated rail crossings in the vicinity (few km) of central is main question of the moment :)