On Car Free Day, all you need to do is buy a single train ticket for one day and you can travel for free on MÁV, GYSEV, Volánbus, HÉV and TramTrain. On trains, the offer is only valid for second class. If the 4-hour ticket is carried over to the previous day (21.09.09) or the next day (23.09.09), it can still be used during the period indicated on the ticket.
