The Bridges of Pittsburgh play an important role in the city's transportation system. Without bridges, the Pittsburgh region would be a series of fragmented valleys, hillsides, river plains, and isolated communities. A 2006 study determined that, at the time, Pittsburgh had 446 bridges. With its proximity to three major rivers and countless hills and ravines, Pittsburgh is known as "The City of Bridges". History Pittsburgh's first river bridges, made of wood and long since replaced, opened in 1818 at Smithfield Street and 1819 at Sixth Street (then St. Clair Street). The city's oldest in-service bridge is the current Smithfield Street Bridge, which opened in 1883; it was designated a National Historic Landmark in 1976. Pittsburgh waged a massive road and bridge building campaign from 1924 to 1940; most of Pittsburgh's oldest major bridges date from this period. The coming of the Interstate Highway System triggered more construction in the second half of the twentieth century, as vehicular speed and throughput requirements increased. The result of more than 100 years of bridge building is a collection of most of the major types of bridge (suspension, cantilever, arch, etc.), mostly built from locally produced steel, including about forty river spans. Many of the bridges in the Downtown area are colored Aztec Gold, either constructed as such or painted afterward, to match the city's official colors of black and gold. A few old and out-of-service bridges, such as the Hot Metal Bridge (which stood dormant until reopening as a passenger bridge in the year 2000), are exceptions to this rule. Degrading bridge conditions According to a 2011 study by Transportation for America, 1,194 bridges in the Pittsburgh area—or 30.4%—were deficient, the highest proportion in the nation. On February 8, 2008, the Birmingham Bridge suffered a failure of its rocker bearings, causing the deck to drop eight inches, prompting a closure of the bridge. The bridge was repaired and fully reopened on September 8, 2008 On January 28, 2022, the Fern Hollow Bridge across Frick Park collapsed, forcing the closure of Forbes Avenue through the park. The bridge was covered with snow when it collapsed at 6:39 a.m. local time as it was being crossed by several cars and a bus. Major bridges This table lists all bridges crossing the Allegheny, Monongahela and Ohio rivers in the City of Pittsburgh limits. Other large or notable bridges are also included. Monongahela River Allegheny River Ohio