The Toronto subway is a rapid transit system in Toronto, Ontario, Canada, operated by the Toronto Transit Commission (TTC). It is a mixed system consisting of three heavy rail lines operating predominantly underground and one light metro line, collectively encompassing 69 stations and 68.3 kilometres (42.4 mi) of track. Since 1954, when the TTC opened Canada's first underground rail line then known as the Yonge subway, under Yonge Street between Union Station and Eglinton Avenue with 12 stations, the system expanded to become Canada's largest in terms of stations and second-busiest after the Montreal Metro. It accommodated an average of 1,066,100 passenger trips each weekday during the fourth quarter of 2015.