Istanbul's public transport system features an interesting aspect regarding "touch interfaces". Two validation solutions coexist in the form of:

AKBIL (deployed in 1995): an electronic transit pass made of a small stainless steel button ("1-Wire Interface") on a plastic holder. Interestingly, from a UX perspective, two or more people can use the same Akbil. The company which provide the solution mentions that " the communication rate and product breadth of iButtons goes well beyond the simple memory products typically available with RFID. As for durability, the thin plastic of smart cards is no match for the strength of the stainless-steel-clad iButton".
Istanbulkart (deployed in 2009): an RFID chip card that is slowly taking off (I have to admit that I haven't seen anyone using it). In this case, the card is personal and enable to take five trips using a single ticket.

Why do I blog this? Transition moment between different technical solutions are always intriguing as both are still in use. The new interface is deployed and users will be encouraged to use it. In this case, given the fact that it's an infrastructure, there's a lot to be done (adding RFID readers here and there).

This transition leads to interfaces with several points of entries as shown on the picture above. The current vending machine still reflects the prevalence of the AKBIL: it's funny to notice how the old AKBIL charging system is convenient (right below where you insert bank notes, which makes the interaction flows more easily).