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I am not sure where else to ask this question, so please close if off-topic (or point to a more suitable place).

I am interested to know what the theoretical highest frequency (i.e. shortest separation time/distance), supported by current train control technology, between consecutive trains is on European, especially German, high-speed railway lines. I would like to use the number to calculate the theoretical maximum throughput on certain routes for a comparison between different transportation modes.

closed as too broad by Giorgio, Ali Awan, Tor-Einar Jarnbjo, Newton, David Richerby Jan 10 '18 at 15:34

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    Most likely, the current frequencies would not give you anything close to the maximum possible throughput. Maybe the railway line supports one hundred trains running 24 hours, but the existing demand is met by four or five trains running only during the day (and of course, there is no need to buy the equipment/hire the staff needed for getting anything close to that maximum). – SJuan76 Jan 8 '18 at 21:24
  • I would suppose that on any European railway, the shortest separation time/distance between trains on the same track is what is needed to stop safely if the train ahead suffers a catastrophic failure. – Weather Vane Jan 8 '18 at 21:38
  • @SJuan76 Good point! I have edited the question to ask for the theoretical maximum allowed by current train control technology. – Cpt Reynolds Jan 8 '18 at 22:45
  • @WeatherVane I agree that would be a deceleration limited minimum safe distance. It would, however, also require interconnected train communication with near-zero lag. I am not too familiar with state-of-the-art train control, but I believe it’s through some centralised entity for each dedicated segment of the line, so the minimum separation allowed by current technology is probably (my assumption) longer than the deceleration limited distance above to ensure adequate margins and system delay. I have therefore edited the question to make reference to current technological capabilities. – Cpt Reynolds Jan 8 '18 at 22:51
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    I'm voting to close this question as off-topic because it's not related to travel – Newton Jan 9 '18 at 12:44
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The capacity of the oldest (and probably busiest) European high-speed line (LGV Sud-Est, Paris-Lyon, France) used to be about 12 trains/hour, i.e. a headway of 4 minutes. It's probably around 15 tph nowadays 

The minimal headway is dependent on the technology used. France has used variants of the TVM system (TVM 300, TVM 430). Now most new lines are equipped with the new ERTMS/ETCS system. There are several different levels with different performances (in terms of max speed, mostly, AFAIK), though deployment of level 2 has been quite difficult and a lot slower than anticipated (see issues on HSL Zuid and others).

It looks like the minimum headway on ETCS Level 2 is about 2 minutes at 300 km/h. The minimum headway increases slightly as speed goes beyond 300 km/h.

Note that the minimal headway is not the only parameter, as you have many other limitations, including coexistence of trains running at different max speeds, supported signalling, station capacity, merging and splitting traffic (with acceleration and deceleration times), mix of non-stop and stopping traffic (ditto), buffers for delays, etc.

It's probably unreasonable to think that you can actually sustain much more than 15 or maybe 20 trains an hour. Note also that this is usually very concentrated on a few hours each day (with specific patterns around the week-end, holidays, etc.).

If you read french, an interesting and very detailed document on the topic (how to increase the capacity on that line to beyond 12 tph) is available here:

http://cgedd.documentation.developpement-durable.gouv.fr/documents/cgedd/2004-0085-01.pdf

Not extremely recent, but I don't think the overall concepts have changed much since then.

You'll understand that the given capacity constraints have led to the development and large scale deployment of the TGV Duplex trains, in order to maximise the number of passengers transported per train path. Two coupled units can carry well over 1000 passengers.

  • In the UK, HS2 is planning to operate 18 tph, which has been criticised as being more than any other existing line, but the system is being intentionally designed around that capacity (including, for instance, every station being purpose-built, no connections to non-high-speed lines, all junctions being fully-grade-separated) for the section that will be operated that frequently (London to Birmingham). This increases costs, but is clearly a lot cheaper than building a second set of tracks – Richard Gadsden Jun 13 '18 at 17:13
  • The Phase 1 service pattern is 10 tph which should definitely not be a problem. 18 tph does indeed seem quite aggressive, especially with all trains stopping at OOC which has only 6 platforms planned. – jcaron Jun 13 '18 at 17:26

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