Identical twins and triplets are uncommon among people, but they are very unusual amongst bridges! So what are the three bridges in Pittsburgh, and are they really identical?
The three bridges (known as the Three Sisters) in Pittsburgh are identical suspension bridges that span the Allegheny River at 6th, 7th, and 9th streets. Built in 1924, the iconic art-deco architecture, Aztec Gold color, and symmetrical lines make them some of Pittsburgh’s best-known bridges.
So why are these bridges identical? Who are these bridges named after? Were they always going to be triplets, or did the plans change? Read on to learn about the fascinating story of Pittsburgh’s three bridges.
Pittsburgh’s Identical Triplets
The city of Pittsburgh is well-known for its astonishing collection of 446 individual bridges. Entire books have been written on the history of Pittsburgh’s bridges, which have sprouted up all along the banks of the Allegheny, Monongahela, and Ohio rivers. Among the city’s many fascinating bridges, three bridges stick out for their startling similarity.
The Three Sisters bridges are three identical bridges located in downtown Pittsburgh that span the Allegheny River. The bridges connect 6th, 7th, and 9th streets across the river, allowing traffic to flow within the city’s grid (such as it is) without having to bottleneck at a singular bridge.
While the bridges are referred to as identical, they are slightly different. This minuscule difference is because each bridge spans a unique section of the river and therefore has some variation in length and width. That said, the designers of the bridges took pains to make them proportionally identical, so they look very, very similar.
Each of the Three Sisters is a self-anchored suspension bridge. This kind of bridge differs from a traditional suspension bridge in that the anchor cables are attached to the road deck rather than being attached to anchorages built outside of the road deck. This technique balances the bridge’s loads in a very stable way, making it popular among engineers.
The Origins of the Three Sisters
Pittsburgh’s bridges have evolved and changed over the years, like the city itself. Before the Three Sisters bridges, there were other, smaller bridges that connected 6th, 7th, and 9th streets. Companies operated these bridges for a profit, which they obtained by charging a modest toll to those who wished to cross the river. In 1911, however, Allegheny County purchased the bridges from their respective owners.
While these smaller bridges had been functioning fine for decades, change was coming. The Rivers and Harbors Appropriation Act, enacted in 1899, allowed the War Department to order bridge owners to modify their structures if they did not meet specific size requirements. In 1917, War Secretary Newton D. Baker declared that the bridges spanning this section of the Allegheny were no longer in compliance with the Rivers and Harbors Appropriation Act and demanded that the county improve or replace them.
The War Department’s interest in these bridges was not just sentimental; it was practical. Since Pittsburgh, a manufacturer of high-quality steel, was a critically important city for the American economy and the American war machine, Baker wanted to make sure that steel and materials could easily flow in and out of Pittsburgh to suit the needs of the War Department.
Bridges and Bureaucrats
Of course, just because the War Secretary says to do something doesn’t mean it will happen immediately. Bridges are complicated and expensive. And since the Three Sisters bridges were being built by the government, politics soon became an obstacle.
First, voters in Pittsburgh didn’t want to spend the money. They reasoned that the existing bridges were mostly fine, and if the War Department wanted to build bridges, they could pay for them. Second, Allegheny County tried multiple times to issue bonds to pay for the bridges, but voters repeatedly rejected this idea.
Finally, in 1924, things changed. Perhaps the old bridges were becoming decrepit, or maybe voters saw the benefits of having modernized infrastructure, but whatever the reason, Allegheny County was able to pass a bond issue successfully. The budget for the three bridges was $29.2 million.
The original plans for the bridges were very different than the bridges that got built. The original designs for the 6th, 7th, and 9th street bridges called for 6th and 9th street to be built as truss bridges and 7th street to be built as a cantilevered bridge.
The bureaucracy, however, had other ideas. At the time, the Metropolitan Art Commission – a small office of the City of Pittsburgh – was required to sign off on any building or structure plans that the public would own. Generally, this was a formality. In the case of the Three Sisters, however, the Art Commission flexed its power and rejected the plans as ugly and impractical, refusing to sign off on them.
Squabbling ensued, but eventually, the engineers and artists found a solution. The bridges were redesigned as self-anchoring suspension bridges. This kind of bridge had a better aesthetic and offered advantages in terms of strength and durability. Now that a suitable compromise had been reached, the real work could begin at last.
Keystone Answers Fun Fact: The Andy Warhol Bridge was the very first self-anchored suspension bridge built in the United States, followed closely by its sister bridges. They are the only trio of identical bridges in the United States!
Who Designed The Three Sister Bridges?
The Three Sisters bridges were actually designed by architects and engineers working for Allegheny County. The architect who designed the bridge was a man named Stanley L. Roush. He was assisted by a design engineer named A.D. Nutter and two structural engineers named T.J. Wilkerson and Vernon R. Covell.
These men may not enjoy the name recognition of architects like Frank Lloyd Wright, but their contributions to the city of Pittsburgh should always be remembered.
Seventh Street Bridge (Andy Warhol Bridge)
The Seventh Street Bridge was the first of the Three Sisters to be completed. It was opened on June 17, 1926. The Seventh Street Bridge spans 1,061 feet from shore to shore and is 62 feet wide.
When it opened, the Seventh Street Bridge was painted gray on the superstructure and green on the deck. However, in 1975, all Three Sisters were repainted with a distinctive yellow color called Aztec Gold.
On March 18, 2005, the Seventh Street Bridge was renamed the Andy Warhol Bridge in conjunction with an anniversary celebration at the Andy Warhol Museum, which is just a hop and a skip from the northern terminus of the bridge.
Ninth Street Bridge (Rachel Carson Bridge)
The second of the Three Sisters to open was the Ninth Street Bridge, which opened to traffic on November 26, 1926. The Ninth Street Bridge spans 840 feet and sits 62 feet wide. Initially, the Ninth Street Bridge was designed to carry two lanes of cars and two lanes of streetcars; the streetcar lanes were eventually converted to automobile lanes.
On Earth Day (April 22) of 2006, the Ninth Street Bridge was renamed in honor of the famed ecologist and Pittsburgh native Rachel Carson, author of Silent Spring. Carson was a renowned scientist, and she used her scientific background and writing skills to help improve environmental awareness and stewardship.
In 2019 and 2020, the Rachel Carson Bridge underwent an overhaul. The road deck was improved and now features three lanes, one in each direction and one “flex lane” that changes direction depending on the time of day.
Sixth Street Bridge (Roberto Clemente Bridge)
Finally, on September 29, 1928, the Sixth Street Bridge opened. It is the second-longest of the three bridges, spanning 884 feet from end to end. Before the Sixth Street Bridge was built, this section of the Allegheny had been crossed by at least three other bridges, all of which had ultimately failed to live up to the needs of the time. That the Sixth Street Bridge is still in use today is a testament to the engineers and workers who built it.
On August 6, 1998, the Sixth Street Bridge was renamed the Roberto Clemente Bridge. Roberto Clemente was a beloved baseball player on the Pittsburgh Pirates. Clemente was a titan of baseball and hugely popular in Pittsburgh.
In fact, before the bridge was named after him, many people in Pittsburgh wanted the Pirates to name their stadium after Clemente. The Pirates, however, sold the name rights to PNC Bank, which called the park PNC Park. Since Clemente had been denied the honor of having his name on the ballpark, the city decided to name the bridge after him.
In the early 2020s, the Roberto Clemente Bridge underwent significant renovations as part of a citywide project to keep Pittsburgh’s infrastructure up to date.
The Three Sisters: An Iconic Pittsburgh Landmark
The iconic design, eye-catching color, and pleasant symmetry of the Three Sisters bridges make them stand out even among Pittsburgh’s many bridges. These identical suspension bridges have spanned the Allegheny and kept Pittsburgh running for a century, but despite their age, the bridges remain both aesthetically pleasing and highly functional. Recent renovations to the Three Sisters will ensure that these Pittsburgh landmarks continue to bridge the Allegheny for centuries to come.