A ticket controller is a person who randomly checks tickets on public transport in systems where one can enter the vehicle without being checked. The system works as follows:

• passenger purchases a ticket
• passenger enters the vehicle and validates the ticket. Sometimes validation is performed when entering platform (Berlin metro)
• a controller randomly enters the vehicle and checks tickets. A fine is imposed if a person without a valid ticket is found.

This system can be found in Berlin metro and largerly in Eastern Europe. It only makes sense if the public transport company can maintain a large ticket sale network, and if execution of fines is possible.

Statistics: in Poznan, Poland the rate of free-riders varies from 4 to 10%.