A paid area usually exists in rapid transit railway stations for separating the train platform from the station exit, ensuring a passenger has paid or prepaid before reaching the railway platform and using any transport service.
The exception is in certain cases of international rail travel, where passengers must also pass through immigration control and customs to enter the paid area.
In some rapid transit systems, passengers are banned from eating or drinking inside the paid area of every station.
A platform ticket allows non-travelers access to the paid area of a station to make a platform tour, seek for departures of friends or relatives, greet friends and family members or to assist them with their luggage without having to have a ticket for a journey.
Similarly, in some airports, such as the Pittsburgh International Airport, non-ticketed members of the public can acquire an airside access pass to visit the shops and restaurants inside the restricted area, as long as they produce a valid piece of identification and go through the security checkpoint.