Comment by Denvercoder9
7 days ago
> What is the cap of throughput is due to these speed limitations is an exercise left for the author of the article.
They already did that exercise:
> 3-car trains running at 30-40 trains per hour (a normal peak frequency for automated or even some human-driven metro lines) reach a capacity of about 18,000 passengers per hour per direction, well above the expected demand of any American line that doesn’t go through Manhattan.
40 trains per hour is in fact not "normal", but extremely difficult. Only a few systems in the entire world operate more than 30 per hour.
The fundamental constraint is not technology, but people and physics: you need to decelerate and stop, let people disembark and get on, accelerate and clear the platform. This cycle requires a bare minimum of 90 seconds, although IIRC a few lines in a few places like Paris and Moscow do 85 secs.
SEPTA's T [1] gets up to 70 TPH and used to handle 150 TPH. You can do this with multiple trolleys loading/unloading on a platform simultaneously.
(But this strategy is orthogonal to the article, because it requires long platforms.)
[1] https://en.wikipedia.org/wiki/T_(SEPTA_Metro)
Indeed, the Victoria line in London manages 36 TPH and we've not bothered beating it since. It's much easier to run 26-30TPH with slightly more carriages.
> the Victoria line in London manages 36 TPH and we've not bothered beating it since
That was a world record for a line following modern safety standards, set less than 10 years ago. It's hardly a case of "not bothered", it's just hard.
90 seconds is very possible in new-build lines which is what the author is talking about. You can buy a turnkey Innovia (e.g. Vancouver Skytrain) or AnsaldoBreda (e.g Copenhagen) that does this out of the box. Retrofitting 90s operation is basically impossible but not the point of this exercise.
Yes, they are assuming a best-case scenario. Driverless systems are very expensive for reasons that have little to do with the cost of the driverless trains, if you're not going to consider those variables this kind of armchair speculation is a waste of everyone's time.
They aren't though? If you're building a new line, fully driverless is pretty much the default these days, especially if the line is fully underground or elevated.
What is incredibly expensive, though, is retrofitting a line designed for manual operation to run automatically instead.
Well, a lot of systems exist that were initially designed for automatic operation but still end up becoming operated manually or partially manually due to safety concerns or politics. Washington DC Metro and BART are the two big systems I can think of that had this issue.
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No, they didn't.
They took "30-40 trains per hour" out of thin air and exercise was to calculate whether it is even possible to have more frequent shorter trains.