Quote:
Originally Posted by st7860
I've never heard of a train in tokyo coming in as little as 30 seconds after a train already left but with skytrain during rush hours it can happen.
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It's the
moving block train control system that makes the close headways possible. With a conventional fixed block system a following train can't get any closer to the train ahead of it than dictated by the fixed track occupancy blocks, and they have to be spaced at least a few train lengths long to allow room for the trains themselves and enough distance to stop.
With the moving block system, the occupancy block "follows" the train as it moves along the track. That means you never have a "worst case" situation where end of the leading train is still a few feet into a fixed occupancy block behind it which prevents the following train from entering that block. So Skytrain consists can always follow each other at very close to the required braking distance.
I'm not sure about this, but I think that moving block systems are exclusive to automated systems, because it seems to me like they pretty much require computer control (no wayside "traffic lights" at fixed points for a driver to see).