“The Lehigh Tunnel is a pair of road tunnels that carries the Pennsylvania Turnpike Northeast Extension (Interstate 476) under Blue Mountain north from Interstate 78 to the Scranton/Wilkes-Barre area between mileposts 70.7 to 71.5. Originally a single tunnel that opened to traffic in 1957, it was called the Lehigh Tunnel to avoid confusion with the existing Blue Mountain Tunnel on the mainline. The tunnel was “twinned” in 1991 to allow two lanes of traffic in each direction. It has an unusual appearance, as the original (northbound) tunnel is rectangular, as it used the older dig-and-blast technique, while the new tube is oval, having been constructed using the New Austrian Tunnelling method.
From 1980 to 1996, the Northeast Extension was designated as Pennsylvania Route 9, as opposing traffic faced each other in the single tube prior to the opening of the current southbound tube, and therefore did not qualify for Interstate highway status, which was granted five years after the completion of the southbound tube.
The Lehigh Tunnel crosses the border between Lehigh County and Carbon County. It is the only road tunnel crossed by the Appalachian Trail.”