A ticket barrier is a mechanical gate used in public transportation systems, such as trains and subways, to control access to platforms and stations. It requires passengers to present a valid ticket or pass before entering or exiting. This helps ensure that only paying customers use the services, enhancing security and revenue for the transport operators. Typically, ticket barriers are equipped with sensors that detect valid tickets, which can be physical or digital. They may also feature a display screen that provides instructions or information. Commonly found in urban transit systems, ticket barriers are an essential part of managing passenger flow and maintaining order in busy environments.