Interestingly, the Toronto subway technically has 24 hour service. It’s just that they’re not actually operated by subway trains. Instead, there are Blue Night bus routes that run along entire subway routes during the night. That seems like a pretty efficient way to do it, since a) it’s cheaper to operate, and b) there are fewer people who ride during the night so the capacity loss is probably no big deal.
Anyway, just wanted to share that tidbit I completely forgot about when writing about the subway. Bye!