Third rail
Like the Orange Line and Red Line, the Blue Line tracks are standard-gauge heavy rail. The Blue Line fleet consists of 94 700-series cars (47 pairs) with stainless steel bodies from Siemens, with each car long and wide, with two pairs of doors per side. Uniquely among MBTA rolling stock, Blue Line cars use both third rail power and pantograph current pickup from overhead catenary wires. The overhead pantograph was implemented to avoid third rail icing that frequently occurs in winter. Third rail power is used in the original Blue Line tunnels, which are smaller than most modern subway tunnels. Trains switch between the two modes at Airport station, near where the line transitions between running in a tunnel and running above ground. Previously, the switchover was made underground at Maverick station.