Bridging Los Angeles - The Bureau of Engineering's documentary on the history of the City of Los Angeles’ bridges over the Los Angeles River.
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 Los Angeles River crossing structures, and the longest of these structures.
Located in a highly urbanized area just east of downtown Los Angeles, the original bridge acted as - and will continue to provide - a critical transportation link between neighborhoods of the Arts District and Boyle Heights. A 1986 Caltrans bridge survey found the original bridge eligible for inclusion in the National Register of Historic Places.
The original Sixth Street Viaduct (designated as City of Los Angeles [City] Bridge No. 53C-1880 and California Department of Transportation [Caltrans] Bridge No. 53-0595 [portion of viaduct over Hollywood Freeway or US 101]) 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.
The original Sixth Street Viaduct was constructed using then state-of-the-art concrete technology and an onsite mixing plant. However, just 20 years after it was constructed the cement supports began to disintegrate due to a chemical reaction known as Alkai Silica Reaction (ASR), causing significant deterioration of the structure.
Over the years, various costly restorative methods have been tried, but none have worked to correct the problem. The results of seismic vulnerability studies, completed in 2004, concluded that the viaduct, in its current state of material deterioration and lack of structural strength, has a high vulnerability to failure as a result of a major earthquake. In addition to its vulnerability to collapse under predictable seismic forces, the Sixth Street Viaduct also had geometric design and safety deficiencies.
The original Sixth Street Viaduct was demolished in 2016 due to seismic-deficiency and deteriorating concrete. The original bridge is being replaced by a new viaduct and is expected to be completed in early 2022.