From the Turnpike's opening in 1940 until the realignment projects, the tunnels were bottlenecks due to reduced speeds with opposing traffic in the same tubes.

[1] After the studies completed, the decision was made to go ahead with a US $100 million [a][2] construction project to work with the tunnels.

Two years after the closing of the Laurel Hill, the Allegheny Mountain became the first tunnel to be twinned, and opened on August 25, 1966.

[1] An engineering report dating back to 1961 suggested that building a bypass around the last two mainline tunnels was the best way to solve the congestion.

All of the original tunnels were part of the never-completed South Pennsylvania Railroad which history has dubbed "Vanderbilt's Folly."

The tunnel was prominently featured in the 2005 music video for the song Foxtrot Uniform Charlie Kilo by American rock band Bloodhound Gang.