The Allegheny River is wider, deeper, and faster than the Seine, and so arch bridges crossing the Allegheny are longer and the arches are often placed above the deck.
The longest deck arch in the world is the New River Gorge Bridge in West Virginia with a span length of 1710 ft (520 m) while the longest through-arch is the Lupu Bridge in Shanghai with a span length of 1,815 ft (553 m). Through arches tend to be longer and they also don't interfere with ship navigation under the bridge. However, they do block the view, which is one reason they were only used at a couple of locations over the Seine in Paris. The other reason is that the technology to build them only became available in the 19th century.
The 16th Street Bridge is composed of three arch spans over the Allegheny River with many simply-supported approach spans over roads, a parking lot, and a railway yard. The total bridge length is 1996 ft (608 m). The main arch span is 420 ft (128 m) long and the side spans are 240 ft (73 m) long. The bridge deck is 41 ft (12.6 m) above the Allegheny River, whose height is determined by the crest of Emsworth Dam a few miles west of the bridge across the Ohio River. At the ends of the arch spans are four tall pedestals that support bronze sculptures.
The 16th Street Bridge was constructed between the two World Wars (in 1922), which is when many of the surviving Pittsburgh bridges were built. The city grew during the American Civil War and went into decline in the last decades of the 20th century. In between, it was a thriving industrial city whose main product was steel. Today, Japan produces the best steel and it is typically shipped to and fabricated in Shanghai.
Pittsburgh Bridges: 16th Street Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.