Union Tunnel (Baltimore)

The Union Tunnel is a pair of railroad tunnels on Amtrak's Northeast Corridor in Baltimore, Maryland that connect Pennsylvania Station to the Pennsylvania Railroad's original mainline to Philadelphia, Pennsylvania and points north. The original tunnel was built in 1873, while a second one was completed in 1934.
Original tunnel.
The Union Tunnel was originally constructed as part of the Union Railroad and served as the northern and eastern approach to Baltimore Union Station (now called Pennsylvania Station). In all, the Union Railroad was in length, extending from the northern terminus of the Baltimore and Potomac Rail Road to the southern terminus of the Northern Central Railway. The junction with the Baltimore and Potomac lies between Pennsylvania Station and the northern portal of the Baltimore and Potomac Tunnel. The Union Railroad joined the Northern Central at Bayview Junction, Maryland on the northeast side of Baltimore.
Although chartered as early as 1866, active steps to finance construction of the railroad and tunnel came only in the autumn of 1870, and actual construction begun May 1, 1871. On July 24, 1873, the first train passed through the tunnel. The original tunnel began at Bond Street, and passed under the bed of Hoffman Street to Greenmount Avenue, crossing under Dallas, Caroline, Spring and Eden Streets, Central and Harford Avenues, and Ensor, Valley and McKim Streets. Its length is . The total cost of the road and tunnel was some $3,000,000.
As soon as the Union Railroad was completed, the Northern Central Railway obtained the right to use it, and in February, 1882, the Northern Central purchased the Union Railroad stock from the Canton Company, and assumed control March 1 of the same year.
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.