Party animals and night workers alike are annoyed when most subways close every night. Here's a complete list of subways that don't.
Why do they close? Since it is common anyways for metro lines to occasionally close for several consecutive days, weeks, or even months for upgrade or construction work, they could as well run at night. The cities listed below easily prove that non-stop operation is technically feasible.
Keeping metros open at night saves cost for staff locking and opening doors or guarding locked stations. It also means better service for passengers who can ride home from bars or parties without the need of always watching the clock, examining timetables, or digging into the intricate details of night bus services.
To be listed here, train services need to operate nightly at least every 60 minutes throughout the year (most of them operate every 10 to 30 minutes). Metro services on special occasions like New Year don't count, bus or tram services don't count as well.