The Cincinnati Southern Bridge, officially the Cincinnati Southern Railroad Swinging Truss Bridge, is a swing bridge that carries the Norfolk Southern Railway over the Ohio River between Cincinnati, Ohio and Ludlow, Kentucky in the United States. The bridge is composed of four through truss spans: a main span on the northern side of the bridge, a currently unused swing span on the southern side, and two additional spans over the main shipping channels in the center of the bridge. The bridge crosses the Ohio River just downstream from downtown Cincinnati, and can be seen clearly from the lower level of the nearby Brent Spence Bridge.
The Cincinnati Southern Railway Bridge was begun in 1875; construction was completed in December, 1877, and the bridge immediately opened to traffic. Its cost exclusive of right of way was $811,683. The 519-foot (158 m) truss bridge was the longest bridge of its type when it was completed.
It was extensively modernized in 1922, and it remains the busiest railroad bridge in the city of Cincinnati today. Since 1976, the bridge's swing span has been abandoned in its closed position, forcing all ships to pass under the center truss spans. For extensively tall ships, the bridge marks the end of their Ohio River voyage.