Pittsburgh City Council on Tuesday unanimously granted historic designation to the city’s three Sister Bridges.

The Roberto Clemente, Andy Warhol and Rachel Carson bridges — also known as the Sixth Street, Seventh Street and Ninth Street bridges, respectively — connect the Central Business District with the North Shore.

The trio were built from 1924 to 1928.

Their origins came after Allegheny County approved $29.2 million in bonds to construct new bridges, roads and buildings to be able to move goods and war materials along its rivers, in response to a 1917 federal mandate that rivers be more navigable. The Sister Bridges are among 41 bridges constructed by Allegheny County in that four-year span.

The bridges mark the first self-anchored suspension spans in the nation and are the only known trio of nearly identical bridges, according to a historic nomination packet prepared by engineering firm Michael Baker International on behalf of Preservation Pittsburgh, which nominated the bridges.

The iconic yellow bridges in 2022 saw the installation of a $6 million LED light project that can display various colors.

The bridges also are listed on the National Register of Historic Places.

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