A station serving South Station was located on the Atlantic Avenue Elevated. Service on the Atlantic Avenue "El" was discontinued on September 20, 1938. The structure itself was torn down in the spring of 1942. Before stairs were added, passengers wishing to change lines from the underground station — itself opened on December 3, 1916 — had to use a paper transfer and go outside to change trains. The underground station had four staircases and one escalator leading from the surface to the mezzanine, and two exit escalators. In 1957, the original fare lobby and the rounded top of the tunnel to the west were removed during construction of the Dewey Square Tunnel. The tunnel was rebuilt with a flat ceiling, while the fare lobby was moved to the east closer to the South Station headhouse. A second renovation began around 1980 and consisted of the adding of a passageway to already existing stairs and escalators upstairs to the main terminal building. An entrance was also added to the Federal Archives Building as well as a passageway under Summer Street connecting the other street entrances. In 1985, the Red Line platforms were extended 60 feet on either end to allow 6-car trains. The final renovation was triggered by the massive highway project known as the "Big Dig". Since the Red Line tunnel beneath Summer Street is perpendicular to Atlantic Avenue, where the new I-93 northbound tunnel was to be built, builders had to tunnel under the tracks. After the first tunnel was complete, another tunnel was added along with a station for the Silver Line. Since the new tunnel was built at the former fare level, another fare level was constructed a level above. This allowed combined access for the Silver and Red lines. The original lobby that was destroyed was replaced by stairways. This project was completed at a cost of $35 million. An additional $13 million renovation of the Red Line level was undertaken. After the first sections of the Silver Line opened in 2002 and 2004, a Phase III was proposed which would build a tunnel connecting South Station and the South Boston Waterfront section with the Washington Street section of the line. In 2010, the project was placed on indefinite hold. However, route, operating to a surface stop on Essex Street at Atlantic Avenue, began service on October 13, 2009. In early 2005, a blue and white tile mosaic reading 'South Station Under' was discovered during renovations to the Red Line platform. The MBTA had the mosaic restored to its original condition during the project. Network, a glass mosaic map by Ellen Harvey, was built on the interior walls of the northeast headhouse in 2019.
Station layout
South Station Under has entrances at street level on all four corners of the intersection of Summer Street and Atlantic Avenue. The Red Line has two tracks and two side platforms on the lower level. Silver Line SL1, SL2, and SL3 service is provided in a tunnel near the Red Line, and SL4 service can be accessed at a surface bus top one block south of the station entrances. stops at Atlantic Avenue and Essex Street near the Bus Terminal. There are also underground passageways upstairs to the inter-city rail station and many restaurants.
Bus connections
Aside from the Silver Line, three MBTA bus routes stop on Summer Street east of the station entrances:
