The tickets may have to be shown or checked automatically at the station platform or when going onto the system, or during the ride by a conductor. Operators may choose to control all passengers, allowing sale of the ticket at the time of ride. Alternatively, a proof-of-payment system allows passengers to enter the vehicles without showing the ticket. Riders may or may not be controlled by a ticket controller. If the rider does not show proof of payment, the operator may fine the rider.