Elon Musk’s Ideas About Transportation are Boring

Re:Elon Musk’s Ideas About Transportation are Boring by njarboe on Saturday December 16, 2017 @09:38PM (#15943697)

How close can you put trains together? For BART it is 24 trains max per hour in the tube and with a new switching and control system they claim they will get up to 30[1]. They go about 60mph. So two minutes between trains. Think about how much space that is: 2 miles between trains. Trains have to carry 100x more people otherwise they would not work at all. Imagine a freeway where cars had to be two miles apart at max density and only going 60mph. You would never see another car while you were driving.

The plan would to be able to pack cars at 100x the density of trains.

[1] https://www.bart.gov/news/articles/2016/news20160502-0

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Re:Elon Musk’s Ideas About Transportation are Boring by jcranmer on Saturday December 16, 2017 @10:15PM (#15943835)

If your signalling and switches are good enough, you can get to about ~30s headways. You can't really go faster than that because station dwell times will screw you. Scheduling this theoretical maximum is a daft idea, though, because any mishaps, and you have no spare time for recovery. Metro systems in practice usually end up being scheduled around 90-150s headway, so about 24-45tph.

There's one catch for trains though: most trains aren't dispatching single cars. Rather, trains on busy systems are generally 8 or 10 cars that move as a consist. If you factor that in to your example, you don't have 120s between cars, but rather 12s. That might sound like a lot, but you should have 3s between cars for safe driving anyways, and train cars carry well over 4× the number of people in individual cars. Even if every road car were full Jitney vans.

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