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.
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 were tried in an ongoing effort to save the structure; all of them failed. 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, had a high vulnerability to failure in the event of a major earthquake. In addition to these risks, the Sixth Street Viaduct had geometric design and safety deficiencies.
The original Sixth Street Viaduct was demolished in 2016. The original bridge is being replaced by a new viaduct and is expected to be completed in Summer of 2022.