Although Pittsburgh is known as the "City of Bridges," local tunnels are just as important in permitting traffic flow into and out of the city.
One of the earliest tunnels constructed in Pittsburgh was the Mount Washington street car tunnel. Opening in December 1904, the 3,498-foot-long tunnel required 12 million bricks, a track bed and rails -- all for $875,000.
Twenty years later, access to and from the South Hills opened up with the opening of the Liberty Tunnel -- or "Liberty Tubes." The tunnel, which goes through Mount Washington, features two tubes that each measure nearly 6,000 feet long. Initial traffic flow exceeded predicted numbers, and during rush hour some motorists began passing out from lack of ventilation. However, by 1928, tunnel engineers designed a system to ventilate the tunnels to accommodate the high traffic flow. Suburban areas such as Brookline, Dormont, Mt. Lebanon and other communities grew substantially after the $6 million Liberty Tunnels opened in 1924.
Residents in the east saw the Squirrel Hill Tunnel open in 1953 as part of the Penn-Lincoln Parkway East. Each side of the twin-bore tunnel measures 4,225 feet long. At the time of construction, the $18 million project was the largest investment by the State of Pennsylvania Transportation Department.
Downtown's Fort Pitt Tunnel, completed in 1960, allows traffic to freely flow from Pittsburgh to the airport. The tunnel, which took about three years to build, is nearly 4,000 feet long and has two lanes in each direction. The Fort Pitt Tunnel sees more than 100,000 vehicles each day and is known for presenting a spectacular view of Pittsburgh's skyline when exiting at the northeast end onto the Fort Pitt Bridge.
The hilly terrain surrounding Downtown Pittsburgh acted as a natural barrier to the city. However, the construction of tunnels provided easy access to Downtown for motorists, eventually leading to the expansion of the region's largest suburbs.