Sixth Street Viaduct

Current Threat to Sixth Street Viaduct

Built in 1932, the two-thirds-mile-long Sixth Street Viaduct is the last and grandest of the monumental river bridges, with its graceful steel arches and clean lines evoking Streamline Moderne design.

The bridge stands as an iconic gateway to both sides of the Los Angeles River and was determined eligible for listing in the National Register of Historic Places in 1986. Featured in countless films, television shows, and commercials, it is the most widely recognized of the historic river bridges. It is also the most imperiled.

According to a report released by the BOE, the bridge has been substantially weakened from a chemical process known as alkali-silica reaction (ASR), which BOE engineers have known about for decades. ASR is a process by which alkali and silica components in the concrete combine with moisture to form a gel that expands, causing cracking and weakening of the structure.

BOE representatives have predicted a seventy-percent risk of the Sixth Street Viaduct's "collapse" in the next major earthquake -- although city engineers have since clarified that "collapse" means that the viaduct would be rendered unusable, not actually fall down. Although a retrofit design was approved and partially implemented in the mid-1990s, the BOE is now pushing replacement as the only truly effective solution.

The Conservancy acknowledges first and foremost the importance of ensuring public safety, but would also like to see a thorough evaluation of preservation alternatives and consultation with bridge engineers who have experience working with ASR before any replacement scenarios might be considered.

In September 2007, the Los Angeles Conservancy submitted detailed comments on the Notice of Preparation of the Draft Environmental Impact Report for the $200 million “Sixth Street Viaduct Seismic Improvement Project.” The initial study identifies only one retrofit alternative, compared to at least four alignments and myriad designs for replacement spans, revealing a bias in favor of demolition.

The Conservancy’s comments ask the BOE to consider at least two retrofit alternatives that meet current safety standards, using different technologies available for treating ASR.

The Conservancy has also proposed a combined retrofit and partial replacement alternative that prioritizes retention of the iconic, arched section of the bridge over the river. Although the viaduct stretches over 3,500 feet, the arched section composes only a small portion of the total length at less than 400 feet.

In February 2009, Conservancy staff attended a presentation by the BOE of their preferred option. BOE staff recommend replacement of the historic viaduct with a new cable-stayed bridge.

We are eager to read the forthcoming Environmental Impact Report so that we can take an informed position on the BOE's recommendation and alternatives.