Until 1984, the Harvard Square stop was the northern terminus of the Red Line, and it still functions as a major transfer station between subway, bus, and trackless trolley. Automobile traffic can be heavy, and parking is difficult. Most of the bus lines serving the area from the north and west run through a tunnel adjacent to the subway tunnel. Originally built for streetcars (which last ran in 1958) and still used by trackless trolleys as well as ordinary buses, the tunnel lessens bus traffic in central Harvard Square, and lets buses cross the Square without encountering automobile traffic. The tunnel also allows safer and covered access between the subway and the buses.