Constructed in 1932, the Sixth Street Viaduct (also known as the Sixth Street Bridge) is an important engineering landmark in the City of Los Angeles. It is one of a set of fourteen historic Los Angeles River crossing structures, and is the longest of these structures.
Located in a highly urbanized area just east of downtown Los Angeles, the bridge is a critical transportation link between LA Arts District and Boyle Heights. A 1986 Caltrans bridge survey found it to be eligible for inclusion in the National Register of Historic Places.
The 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]) has an overall length of 3,500 ft., and extends east-west across the Los Angeles River, multiple railroad tracks, US 101, and several local streets. It has 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 are sidewalks of varying widths on both sides.
The Sixth Street Viaduct was constructed using then state-of-the-art concrete technology and an onsite mixing plant. However, just 20 years after the Sixth Street Viaduct 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 has geometric design and safety deficiencies.
The City of Los Angeles is the owner of 533 structures, which include: 124 vehicular, 65 pedestrian 2 bikeway, and 19 railroad bridges, viaducts, and grade separations; 18 tunnels, and 5 miscellaneous structures that span waterways, roadways, railroad tracks, and valleys between prominent topographical features. Twenty-nine of these structures have been determined to be eligible for listing by the National Register of Historic Places (NRHP).
In December 2000, the City Council approved a $307 million Bridge Improvement Program (BIP), created within the Seismic Bond, to strengthen and upgrade 83 city-owned bridges. BIP was envisioned to be a long term continuous program, similar to the Bureau of Engineering's Street Program, to improve all bridges within the jurisdiction of the City.
The program is tasked to seek new sources of funding as they become available and to program new projects by working closely with Caltrans, LADOT, Metro, and FHWA staff. Funding is typically comprised of Highway Bridge Program (HBP) funds, with Local Seismic Safety Retrofit Program (LSSRP) state funds and Seismic Bond city funds serving as the local match. These funded projects are then leveraged to obtain additional Metro Call-for-Projects dollars and city Proposition C matching funds to cover expanded scopes of work such as bikeway and pedestrian improvements.
One of the projects in the BIP is the replacement of the Sixth Street Viaduct, a $420 million undertaking.