Aquarium Station of the MBTA, is a station on the Blue Line, serving the New England Aquarium and Boston's Financial District..The Blue Line is standard gauge heavy rail..Blue Line cars are unique among rapid transit vehicles in Boston in that they use both third rail and overhead pantograph current pickup. The line switches between the two at the Airport station where it transitions between running in a tunnel and running above ground. The overhead pantograph was implemented to avoid the third rail icing that frequently occurs in winter. The Blue Line fleet consists mainly of 94 700-series cars (47 pairs) with stainless steel bodies from Siemens, with each car 48 feet (14.9m) long and 9 feet 3 inches wide (2.8m), with two pairs of doors per side. The cars are of a similar design to those built for the Tren Urbano system in San Juan, Puerto Rico, also designed by Siemens. Originally scheduled to be delivered beginning in January, 2004, the development of the trains has been beset with problems. The contract price of the cars is $174 million, with a total cost to the MBTA (including engineering and other related services) of $200 million.