[tazjin]

Moscow metro does this. In very busy stations only the turnstiles at the sides have this functionality though, as the native NFC cards ("Тройка") are much faster (contactless payments can take O(seconds), which is a lot when there's 50k people trying to get through).

[Symbiote]

London managed to make the contactless payment almost as fast as the native (Oyster Card) payment.

It is perceivably slower, I'd estimate 0.8 seconds vs 0.5 seconds or something like that.

Close enough that one person trying to use the wrong turnstile would remove any benefit from separating them. Anyway, 60% of passengers use it now.

[tazjin]

I remember contactless being okay in London when I lived there, but I'd always switch queues immediately if someone pulled out a phone to pay. Those people frequently need a good five seconds to pay ...