high tides and storm surges. The proposed North-South Rail Link includes a possible Central Station for MBTA Commuter Rail trains located under Aquarium station. Station layout Aquarium station is located under State Street at its intersection with Atlantic Avenue, near the edge of Boston Harbor. The station has two side platforms—each long enough for six-car trains—serving the two tracks of the Blue Line. The platforms are below street level, making it the second-deepest station on the MBTA system after Porter station. The Tip O'Neill Tunnel, which carries Interstate 93, passes over the center of the station and is supported by its roof. The older eastern part of the platform level has an arched ceiling, which widens to a triple vault in the newer western section. Mezzanines with faregates are located at both ends of the station. The east mezzanine is located on the west end of Long Wharf, near the New England Aquarium. Two glass headhouses—one with escalators and stairs, the other with an elevator—provide access from the surface. The west mezzanine is located under State Street west of Atlantic Avenue, near the Custom House Tower. That mezzanine is accessed by a headhouse—which includes an elevator—on the south side of State Street, as well as a smaller entrance inside a building on the north side of the street. The station is also served by the MBTA bus route , which runs on Atlantic Avenue at peak hours. Aquarium station is the primary transfer point between the MBTA subway and ferry services on Boston Harbor: MBTA Boat routes F2H and F4 plus East Boston service terminate at Long Wharf, as do several Boston Harbor Islands ferry routes. History State Street station Construction of the Atlantic Avenue Elevated began on January 21, 1901. The Boston Elevated Railway (BERy) opened the line on August 22, 1901, including a stop at State Street. Like the other four stations on the line, State Street had a single elevated island platform with a single mezzanine underneath. Passengers entered the station from staircases on either side of Atlantic Avenue north of State Street, and exited on two staircases to the south. The platform was originally three cars—about —long; an extension to allow four-car trains was completed on June 13, 1902. Atlantic Avenue station On May 5, 1900, the Boston Transit Commission (BTC) began construction on the East Boston Tunnel—a streetcar tunnel between East Boston and downtown Boston