sentences:  The Rachel Carson Bridge is one of the "Three Sisters" Bridges, opened between 1926 and 1928, and designed by County architect Stanley L. Roush and the Allegheny County Department of Public Works.The Roberto Clemente Bridge (formerly Sixth Street Bridge) and the Andy Warhol Bridge (formerly Seventh Street Bridge) complete the trio of bridges.They are the only trio of nearly identical bridges and were the first self-anchored suspension spans built in the United States.