Bus smart ticketing systems and EMV

I have recently started to study the smart ticketing systems. Most of the modern systems support the use of EMVCo standards for buying tickets in the bus. Also, in each bus usually there are more than one devices from which a passenger can buy a ticket. In my opinion these devices exchange data related to the bank cards, e.g. the validator must send some data to the main pc in the bus (on board unit, obu) when a passenger buys a ticket, and of course all the data are sent to the back office. I think that these data must be encrypted to prevent eavesdropping. Does anyone have any idea if there are any standards that specify the type of this encryption? I ve read about PCI standards and point to point encryption but I am not sure that these are applicable in smart ticketing systems.