Comment by lmm
7 days ago
How would that help? 3 minutes is the minimum separation distance, if the trains have different stopping patterns then that just means they'll be further apart for part of their journey. If you have to stay 3 minutes behind the train in front, you might as well stop at all the same stations that it does, you can only save time if you were further behind to start with, so you can't increase throughput by skipping stops.
Simplifying a bit, its because the train behind can be scheduled 3 min after the train ahead has pulled in rather than 3 min after the train ahead pulled out. Put another way, the safe stopping distance to maintain (while at speed) would be measured from the half way point of the platform rather than the start of the platform.
This lets you schedule them much closer together than the conventional 3 min while still being safe.
> its because the train behind can be scheduled 3 min after the train ahead has pulled in rather than 3 min after the train ahead pulled out.
Why? If the minimum is 3 min then it's 3 min (at least with a modern moving-block type setup). If it's safe to run them 2 min apart it's (generally) safe to run them 2 min apart the whole time.
The 3 minute minimum is based on the premise that there needs to be enough space for the front of the train behind to stop before reaching the rear of the train ahead. But if the stations are split into two boarding areas like I've proposed then the front of the train behind was already scheduled to come to a stop before reaching the rear of the train ahead of it. Thus there's no need to create even more separation than they already have by spacing out the schedule.
Put another way, the 3 min normally starts ticking from the moment the train ahead completely clears the station (as in the rear of it passes the end of the platform), but in the dual-boarding setup the 3 min starts ticking from the moment the train ahead comes to a halt (as the rear of it has already passed the end of the first boarding area).
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