permit to purchase

In the ticketing system of the British rail network, a Permit to Travel provisionally allows passengers to travel on a train when they have not purchased a ticket in advance and the ticket office of the station they are travelling from is closed, without incurring a penalty fare.
Because some rail passengers may travel without having their tickets checked at any point of their journey, particularly at off-peak times when stations are less likely to be staffed, the obligation to possess a Permit to Travel allows the collection of at least some revenue from passengers who would otherwise travel for free. Most train operating companies (TOCs) have altered their penalty fare policies and have removed many Permit to Travel machines. At larger stations, these stations have also in recent years given way to more sophisticated self-service ticket machines.

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