The Allegheny Mountain Tunnel is a vehicular tunnel carrying the Pennsylvania Turnpike through the Allegheny Mountains. At this point, the Turnpike carries Interstates 70 and 76. The original Allegheny Mountain Tunnel was built in the late 1800s for the South Pennsylvania Railroad, which was never completed. This tunnel was not used due to concerns about its structural integrity.
The eastern end of this original tunnel can be seen by parking on the service road at the turnpike's eastern portal and walking up to the area just above and a bit north of the turnpike portal. The opening is visible in the rocks just uphill. Entering this old tunnel is not recommended.
The current westbound tunnel was built in 1939 as part of the original construction for the highway. At first, this tunnel served both westbound and eastbound traffic with a single lane in each direction. The eastbound tunnel was completed in 1965 as part of an expansion and upgrade of the turnpike due to increased traffic volume. Both tunnels are approximately 6070 feet (1850 m) in length. Explosives and other hazardous materials are not allowed in the tunnels. Vehicles carrying these materials must exit before the tunnel and take other roads around the tunnel. Restrictions on some hazardous materials in non-bulk form have been lifted.
Long term plans call for major maintenance to be performed on the tunnels; however, this presents a major problem for traffic. Terrible backups prompted officials to build the second tube. With today's traffic volumes, it would not be feasible to close one tube and route all traffic through the other. Possible plans include building a third (and possibly a fourth) tunnel, as well as bypassing the tunnels completely as was done for the Rays Hill and Sideling Hill Tunnels.