[beAbU]

We have this in South Africa, on the service between Pretoria and Johannesburg called the Gautrain.

It works with tap cards, both debit and credit. Can even be used to get in and out of the parking by tapping at the boom gate at entrance/exit.

You can buy a special Gautrain card that uses the same hardware. But the only benefit of the dedicated card is for folks that travel frequently, as you can buy discounted prepaid fare, something like 40 trips to be used in 20 days, for half price.

Only real risk is if you carry both a credit and debit card, and mix them up during the scan in/out process. They then charge maximum fare on both cards.