The metro transport system is designed to transport a large number of passengers on the urban transport backbone lines. The metro check-in system must; therefore, provide enormous passenger throughput, which is often random.
Unlike the BRT systems and rail transport, it does not place such demands on weather resistance. However, high throughput is essential for transport peaks handling.
Turnstiles and gates do not serve as barriers to entry, so swing gates or even better flap gates are most often used. They provide much greater passenger throughput. They can also work in a specific mode, where the door is not opened for every passenger separately, but is open by default and closes only if the passenger does not check in with his valid document. Thanks to its turnstile sensors system, it can detect the individual persons in a continuous row of passengers and prevent multi-passenger passages.
The other check-in devices used in metro systems include ticket machines, multifunctional terminals, and stationary validators.