Constructed in 1932, the original Sixth Street Viaduct (also known as the Sixth Street Bridge), was an important engineering landmark in the City of Los Angeles. It was one of a set of fourteen historic structures crossing the Los Angeles River, and the longest of these structures.
Located in a highly urbanized area just east of downtown Los Angeles, the original bridge acted as a critical transportation link between the neighborhoods of the Arts District on the west side and Boyle Heights on the east side.
The original Sixth Street Viaduct had an overall length of 3,500 ft., and extended east-west across the Los Angeles River, multiple railroad tracks, US 101, and several local streets. It had a 46-foot wide, four-lane roadway with 11-foot eastbound and westbound inside traffic lanes and 12-foot outside lanes with no shoulders. There were sidewalks of varying widths on both sides.
Due to its large size, the original Sixth Street Viaduct was constructed using an onsite concrete mixing plant. Unfortunately, the aggregate used in the concrete caused a chemical reaction known as Alkali Silica Reaction, which caused deterioration of the concrete structure within 20 years of its completion.
Over the years, various costly restorative methods were tried in an ongoing effort to save the viaduct; all of them failed. Seismic vulnerability studies concluded that the viaduct had a high vulnerability to failure in the event of a major earthquake, along with geometric design and safety deficiencies. Studies showed it needed to be replaced.
The original bridge is being replaced by a new viaduct and is expected to be completed in Summer of 2022.