The Winter Street Concourse is a pedestrian tunnel in Boston, Massachusetts connecting the Park Street and Downtown Crossing subway stations of the MBTA. It can be used to pass freely between these two major transfer stations without boarding a Red Line train, and is therefore a means of transfer between the Green and Orange lines (this is also possible at Haymarket).
The tunnel was constructed in 1915 but not opened to the public until 1978; before then it was used for storage and offices.
Page on the Red Line tunnel at nycsubway.org (http://world.nycsubway.org/us/boston/red/mbta-red-downtown.html) including information on the concourse
100 years of the Tremont Street Subway (http://members.aol.com/netransit/private/tss/tsstext.html), mentions date of origin and opening
