In the UK, the older generation of readers are pretty slow. The newer models are pretty fast, I'm not sure if it's also because they have reliable broadband connections but they basically ask you to remove the card almost as soon as you insert it.
We have the same console as I've seen in Tesco petrol station. Ours take a lot longer for auth, I'm guessing that Tesco have a local stopped card list to check against and don't do a full auth with the bank in order to save time.
Might be wrong, just my assumption based on contactless payment being almost instantaneous (like that petrol station).
I'm pretty sure that Transport for London do something similar (ie: transactions get batched and then charged at end of day, blacklisting for bad cards).
However, using a contactless chip card is still a lot slower compared to using an Oyster card. Where as the Oyster card seems to process in a matter of milliseconds, the contactless card takes perhaps 2 seconds or more.
With a long queue of people all using contactless, this potentially adds up to quite a significant delay at the ticket gates.
It would help if they had more Oyster readers and/or better situated ones - at one popular station I use, there's two readers, side-by-side, right next to a tiny exit hole. Even just moving those two a couple of metres apart would improve the flow of humans greatly.
Oyster cards are settled between the reader and the card at the time of contact (then the reader will batch the transactions for forwarding later). POS are generally settled on the switch network, obviously this takes a lot longer.
TfL can and do batch contactless transactions, too.
The charge for travel on a given day is not made against your account until early the next morning. And card readers on buses, for example, don't always have a reliable data connection, so must be able to be processed offline.
You might be right that they are authorising in real time on the Tube readers, though. This would explain the poor performance.
The ones that use GPRS can also be _fairly_ fast, though it introduces a couple of seconds of unavoidable latency. They're not long for this world, though; some countries are already shutting down GPRS networks.
The really slow ones just used dial-up. They mostly seem to be gone now.
