Public transport
For most–but not all–public transport systems, passengers must buy a ticket. Tickets may either be bought before the ride, at the time of the ride, or both. Tickets can be paper ticket, metal or plastic tokens, or an electronic card (smart card, contactless smart card). Sometimes, a ticket has to be validated (marking the time of the ticket's use). A paper ticket is stamped when it is validated. An electronic ticket is checked in.