Three Sisters (Pittsburgh)

The Three Sisters
View of Sixth, Seventh and Ninth Street Bridges from downriver
Coordinates	40°26′46″N 80°00′07″W / 40.44611°N 80.00194°W / 40.44611; -80.00194
Carries	2 Vehicular lanes, 2 sidewalks
Crosses	Allegheny River
Locale	Pittsburgh, Pennsylvania
Maintained by	Allegheny County
Characteristics
Design	Self-anchored suspension bridge
Pittsburgh Landmark – PHLF
Designated	1988[1]
Location

Sixth Street Bridge
From north bank of the Allegheny, downtown Pittsburgh in background
Coordinates	40°26′43″N 80°00′12″W / 40.44528°N 80.00333°W / 40.44528; -80.00333
Carries	Sixth Street
Official name	Roberto Clemente Bridge
Characteristics
Total length	884 feet (269 m) in main plus two 215 feet (66 m) side spans; 995 feet (303 m) with approaches
Width	38 feet (12 m) roadway (formerly 2 vehicle, 2 tramway tracks, now 2 wide vehicle lanes) with 10 feet (3.0 m) sidewalks outside the plate girders
Longest span	430 feet (130 m)
Clearance above	78 feet (24 m) towers
Clearance below	deck is 40 feet (12 m) above Emsworth Dam normal pool level or 710 feet (220 m) above sea level
History
Opened	October 19, 1928; 95 years ago (1928-10-19)

The Three Sisters are three similar self-anchored suspension bridges spanning the Allegheny River in downtown Pittsburgh, Pennsylvania at 6th, 7th, and 9th streets, generally running north–south. The bridges have been given formal names to honor important Pittsburgh residents:

• Roberto Clemente (Sixth Street Bridge)
• Andy Warhol (Seventh Street Bridge)
• Rachel Carson (Ninth Street Bridge)

Designed by the Allegheny County Department of Public Works, they were all built in a four-year period, from 1924 to 1928, by the American Bridge Company, replacing earlier bridges of various designs at the same sites. Their construction was mandated by the War Department, citing navigable river clearance concerns. They are constructed of steel, and use steel eyebars in lieu of cables.

The Three Sisters are historically significant because they are the only trio of nearly identical bridges, as well as the first self-anchored suspension spans, built in the United States. They are among the only surviving examples of large eyebar chain suspension bridges in America, and furthermore, unusual for their self-anchoring designs. The bridges’ design was viewed as a creative response to the political, commercial, and aesthetic concerns of Pittsburgh in the 1920s.

The bridges were designed under the auspices of the Allegheny County Department of Public Works, by T. J. Wilkerson, consulting engineer; Vernon R. Covell, chief engineer; A. D. Nutter, design engineer; and Stanley L. Roush, architect. The American Bridge Company built the superstructure, while the Foundation Company built the substructure. All three bridges are owned by Allegheny County.