This diagram shows prospective subway cross-sections.
As built, all sections of the Central Parkway subway
as well as the suburban tunnels were built to the double
tube design at top. No sections were built as a single
tube, except for the exceptionally wide section under
Central Parkway between Elm St. and Vine St., to either
side of the Race St. Station. In that area, the
subway is 3 tracks wide, and the roof is supported by two
parallel rows of pillars, and looks much like a typical
underground parking garage.