The Blue Line of Boston's MBTA uses third rail electrification from the start of the line downtown to Airport station, where it switches to overhead catenary for the remainder of the line to Wonderland. The outermost section of the Blue Line runs very close to the Atlantic Ocean, and there were concerns about possible snow and ice buildup on a third rail so near to the water. Overhead catenary is not used in the underground section, because of tight clearances in the 1904 tunnel under Boston Harbor. The MBTA Orange Line's Hawker Siddeley 01200 series rapid transit cars (essentially a longer version of the Blue Line's 0600's) recently had their pantograph mounting points removed during a maintenance program; these mounts would have been used for pantographs which would have been installed had the Orange Line been extended north of its current terminus.