An infill station is a train station built on an existing passenger rail, rapid transit, or light rail line to address demand in a location between existing stations. Such stations take advantage of existing train service and encourage new riders by providing a more convenient location. Many older transit systems have widely spaced stations and can benefit from infill stations. In some cases, new infill stations are built at sites where a station had once existed many years ago, for example the Cermak–McCormick Place station on the Chicago 'L''s Green Line.

Arlington station is an underground light rail station on the Massachusetts Bay Transportation Authority (MBTA) Green Line located at the southwest corner of the Boston Public Garden at the corner of Arlington and Boylston Streets at the east end of the Back Bay neighborhood of Boston, Massachusetts. Arlington station was not included in the original construction of the Boylston Street subway, which opened in 1914. Its construction was delayed by World War I, and the station ultimately opened in 1921.