The Sixth Street Viaduct (1932, 3546’) At two thirds of a mile long, the Sixth Street Viaduct is the longest, as well as youngest of the Los Angeles River bridges. With its pair of sweeping steel arches and unique Classical Moderne design, it is considered by many to be the Crown Jewel of the bridge collection. The future of this remarkable structure looks bleak. Afflicted with alkali-silica reaction (ASR), a chemical reaction which affects the structural integrity of concrete, the bridge structure has been substantially weakened. The Bureau of Engineering is pushing for an expedited and thorough bridge replacement. Many members of the community are hoping for alternative options.