The Green Line is a light rail system run by the Massachusetts Bay Transportation Authority (MBTA) in the Boston, Massachusetts, metropolitan area. It is the oldest Boston subway line, with tunnel sections dating to 1897. It runs underground through downtown Boston, and on the surface on several radial boulevards and into inner suburbs. With a daily weekday ridership of over 220,000 in late 2014, it is the most heavily-used light rail system in the country.