ON THIS DAY: December 20, 1919, Construction begins on Liberty Tunnels

PITTSBURGH, Pa. — Pennsylvania Gov. William C. Sproul came to Pittsburgh to see the groundbreaking ceremony for the Liberty Tunnels on Dec. 20, 1919. After a procession through the South Hills, officials kicked off the construction of the tunnels with a ceremonial blast of dynamite on the face of Mount Washington.

Prior to the early 1920s, getting downtown from the South Hills was a tedious and circuitous route. The only bridges that crossed into the triangle were the Point Bridge and the Smithfield Street Bridge. The Smithfield Street Bridge also connected by trolley lines to the only tunnel, which was exclusively used for the trolleys.

With the automobile age approaching, the Pittsburgh Committee on City Planning hired Frederick Law Olmsted in 1901 to study ways to improve the traffic routes. His report included recommendations to build what would later become the Boulevard of the Allies and a bridge-and-tunnel to connect downtown and the South Hills directly.

Olmsted followed earlier requests from South Hills residents and expanded on them, suggesting a double-decked bridge that would rise dramatically from downtown on a grade of approximately 3.5% and pierce Mount Washington 80 feet higher than the Liberty Tunnels do today. The southern portals of his proposed tunnels would have been near the present day intersection for E. Warrington Avenue (named Washington Avenue at that time) and Haberman Avenue. A lower deck to the bridge would have skewed farther down and connected with East Carson Street.

City planners took Olmsted’s recommendation that the route be prioritized as “eminently desirable,” but with significant changes. Olmsted’s plan would likely have been cheaper due to a shorter tunnel, but the bridge was thought to be too steep and high. In the end, it didn’t matter, because World War I put plans for the bridge on hold even as the tunnel boring moved forward.

The Liberty Tunnel was the first tunnel specifically designed for automobile traffic and remained the longest in the world until the (as yet unnamed) Holland Tunnel opened in New York City shortly afterward. Residents watched expectantly over the next four years as over 400,000 tons of dirt and rock were blasted and removed.

At the time of its construction, engineers didn’t have a lot of experience in determining how much pollution cars emitted or how much fresh air would need to be pumped in to offset it. The closest estimations for ventilation were based on train tunnels, which didn’t account for stoppages within them, and on research conducted by the Bureau of Mines. Engineers knew they needed ventilation in the tunnels (and the Liberty Tunnels would become the first artificially ventilated tunnels), but the original system was undersized and not operational when the tunnels were completed. There also simply wasn’t a lot of research available to determine how much carbon monoxide a person could breathe before it became dangerous.

After much public debate about the adequacy of the ventilation system’s design, the tunnel opened to traffic soon after the chief engineer of New York’s new tunnel, Clifford Holland, said it was sufficient. Calculations at the time relied on a steady traffic flow that created a natural draft of air in addition to the incomplete and nonfunctional ventilation system. The mistake was compounded by the Pittsburgh Department of Public Works, which had based the Liberty Tunnel’s flow rate on traffic measured on Bigelow Boulevard.

When 3,200 trolley motormen and conductors for the Pittsburgh Street Railway Company went on strike at midnight on May 10, 1924, downtown commuters had no other option than to flood the roadways with cars. At that time, the Liberty Bridge had not been built yet, so traffic exiting the tunnels had to snake down to the Smithfield Bridge to cross the river into downtown, which caused massive delays, even for a Saturday.

It didn’t take long for the congestion to back up into the tunnel itself and, not long after that, the fumes from all the stopped cars began to gather in the stagnant air. The Pittsburgh Press reported that 649 cars jammed into the tunnel.

Hearing horns honking from panicked drivers, police officers scrambled into the tunnels, telling drivers to shut off their engines, but it was too late and drivers began slumping over their steering wheels of carbon monoxide poisoning. Other gasping drivers fled their vehicles, which left them idling and spewing out more exhaust into the growing fog.

Miraculously, no one died in the thick air. First responders fought for more than an hour to evacuate the tunnel and police officers using wet handkerchiefs as gas masks had to be rescued by their comrades when they too collapsed.

A total of 33 people had to be hospitalized for carbon monoxide inhalation.

The tunnel was cleared of vehicles and reopened later that afternoon but with new restrictions. Until the ventilation system was fully operational, police would only allow six cars per minute to enter the tunnel. It took until 1928 for engineers to get the ventilation system capable of keeping the tunnel air clear even when traffic was packed inside.

Today, eight 12-foot-diameter fans are connected to a large brick utility building on Secane Avenue on Mount Washington by 200-foot high shafts. The shafts exit the building into four towering 110-foot-tall square stacks and the system can maintain a 15 mph airflow through each of the tubes.

For commuters to downtown, the tunnels only solved half of the problem. Drivers exiting the tunnels were confronted with open river ahead of them and both portals turned abruptly to connect to Arlington Avenue for four years until newly elected county commissioners took up completing the route with gusto and drafted bond measures to fund the construction of the Liberty Bridge.

City Councilman P.J. McArdle, a Mount Washington resident, also cast his eyes on the newly opened Liberty Tunnels and lobbied for a road that would connect to them. The route proved challenging and would not be completed until 1938 and the road was renamed for him after his death in 1940.

The Department of Public Works took up the challenge of designing the bridge. Allegheny County bridge engineer George S. Richardson, a 28-year-old draftsman at the time, is credited with doing most of the design work. Richardson would become known for designing many of the region’s bridges during his career, including the McKee’s Rocks, Homestead High Level, Westinghouse Memorial, West End, Fort Pitt and Fort Duquesne.

While the southern bridge approach was evident, the complicated northern approach required greater scrutiny. Integrating the bridge with existing city streets required an 80 foot deep cut through the bluff along Shingiss Street with the remaining earth and shale held back by a large, sloping reinforced concrete retaining wall. The wall is between 18″ and 36″ thick and remains to this day, protecting the Crosstown Boulevard below it and supporting Duquesne University above it.

A grand opening celebration was held on March 27, 1928. A parade that stretched fives miles long wove its way from Mt. Lebanon all the way to the southern tunnel portals, where speeches were given. The parade route and bridge were festooned with flags and bunting. It was the largest automobile procession in Pittsburgh history, which proved symbolic as it effectively marked the end of the streetcar’s prominence.

With the easy passage to downtown through the Liberty Tunnels and across the Liberty Bridge complete, development in the South Hills exploded. What had previously been sparsely settled neighborhoods clustered around trolley stops dramatically changed into an extensive patchwork of some of Pittsburgh’s most populated suburbs as housing developments stretched to Allegheny County’s southern border and beyond.

At the time it was completed, the 2,633-foot Liberty Bridge was the longest, highest and most expensive bridge in Allegheny County. It has 16 total spans, with two main cantilevers and trusses to leap over the former rail yards on the southern bank of the Monongahela River and city streets on the northern approaches.

On the southern end, it originally featured a traffic circle with a commemorative monument between the bridge and tunnel. The roundabout was often patrolled by a traffic officer who monitored the flow, with vehicles from McArdle Roadway mixing in and out.

The northern end of the bridge’s Boulevard of the Allies approach ramp from Grant Street is notable for twin Doric columns topped by American eagles at the top. The granite columns are carved with more patriotic symbols and a dedication statement that reads: “To commemorate the deeds of valor and sacrifice of those who contributed to the successful termination of the World War and to the abiding hope of an enduring peace this boulevard is dedicated.”

The original design of the bridge had ornate wrought-iron handrails that flowed into street lights. During a rehabilitation of the bridge in 1983, the bridge was widened from its original 38 feet to 56 feet by cantilevering the deck and those decorative elements were removed. New crash barriers for vehicles were installed and about four million pounds of repair steel was welded onto the bridge. It was also repainted from silver to Aztec gold, matching other Pittsburgh bridges.

Since the Liberty Bridge’s steel cantilevers are not visible to the casual user and its structure is hidden beneath the broad decking, the engineering significance of the span and the bridge’s importance is easily forgotten. The bridge itself is hardly noticed and can easily be thought of as just a brief conduit between the more visible Liberty Tunnels and downtown.

In a real-world example of “You don’t know what you have until it’s gone,” Pittsburghers were stunned when a massive fire broke out during bridge reconstruction work on Sept. 2, 2016. Errant sparks from a welder ignited plastic ventilation pipes and quickly spread to the large tarps covering the structure. Huge plumes of acrid smoke filled the sky as people flocked to windows and saw the landmark blazing.

Intense heat from the flames caused a major steel beam to buckle, and engineers later said the bridge was potentially minutes from collapsing. Fire officials later estimated the fire burned at more than 1,200 degrees.

The bridge was immediately closed to all traffic for the first time on a weekday since it opened. It would remain closed for over three weeks. The city was treated to a reminder of how impressive and important the long taken-for-granted bridge’s structure is, carrying about 55,000 vehicles daily.

After extensive analysis, the bridge was found to be several inches out of position and experts from CMU and Lehigh Universities designed a pair of 26.5-foot braces to stabilize the bridge after jacking it back into its rightful place. The repairs were completed at great expense to the bridge’s contractor, Joseph B. Faye Co., which also had to pay fines of $213,000 every day that the bridge was closed.

The bridge reopened with weight restrictions for a time, before fully reopening after the new braces were in place.