Modifications
Additional work was done on the tunnels between 1928 and 1935 to prepare for the electrification of the Pennsylvania Railroad's New York-Washington mainline. The original Union Tunnel, too small to accommodate overhead catenary on its two tracks, was supplemented by an adjacent double-track tunnel to the east, then converted to a single track which provided adequate clearance for electrification. Coordinates: 39°18′21″N 76°36′32″W / 39.3058°N 76.6088°W / 39.3058; -76.6088
Read more about this topic: Union Tunnel (Baltimore)