Los Angeles Sixth Street Viaduct Replacement – Honor Award

2023 DESIGN AWARD RECIPIENT

Los Angeles Sixth Street Viaduct Replacement – Honor Award

The Sixth Street Viaduct (also known as the Sixth Street Bridge) has been designed by Michael Maltzan Architecture for the City of Los Angeles to replace an iconic but rapidly failing structure built in 1932. The viaduct, called the Ribbon of Light, creates a dramatic new urban symbol for LA while bringing much needed new community resources to the area. The design evolves the monoculture of a single-‐use bridge into an intermodal multiculture welcoming motorists, cyclists, and pedestrians alike. It seeks to overcome the silo effect caused in the past by infrastructure, countering it with the vibrancy and connectiveness of a “civic structure.”

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Infrastructure as architecture, not just a bridge but a civic unifier. This project exemplifies how a complex piece of urban infrastructure can be reimagined and turned into a space for the city addressing environmental issues, and celebrating social and cultural diversity.

Noteworthy performance features include:

1. Platinum certification from the Institute for Sustainable Infrastructure

2. Project is highly focused on its community impact and restoration of urban spaces

//framework for design excellence measures

Measure 1: Design for Integration

The Viaduct is equal parts architecture and engineering. It is defined by ten pairs of concrete arches and a cable supported roadway. The arches tilt outward and are constructed segmentally, the deck has an efficient, thin profile. Foundations at each pier are nearly identical, improving efficiency.Open space below the Viaduct will become a new and needed community park. 5 stairways that connect to the ground increase connectivity and allow for flexibility. Public activity space is under the eastern portion, and two bike ramps and a River Gateway path link the River to the Arts Plaza. 100-year service life and Platinum certification from the Institute for Sustainable Infrastructure, its highest award.

Measure 2: Design for Equitable Communities

The viaduct is designed to serve multiple purposes: Ensure greater public safety, preserve mobility and encourage multimodal travel; Instill civic pride and sense of place as a world-class LA icon; Increase transportation equity in Boyle Heights; Unify Boyle Heights with Arts District; Provide safe, direct access to a future 12-acre public park below; Instantly transform into a civic event space; Serve L.A. for the next 100 years with minimal maintenance.
The new Sixth Street Viaduct will also provide a cinematic backdrop for movies and everyday life for generations to come.

Measure 3: Design for Ecosystems

The Viaduct sits in a seismically vulnerable area. The project team selected seismic isolation and developed a new seismic isolation methodology that improves seismic isolation bearing reliability from existing standards and, in the process, set a worldwide precedent for seismic safety. The design features a new application of seismic isolators placed at mid-height in the viaduct’s 18 Y-bents, a U.S. first for bridges. A total of 32 isolators, placed at columns, abutments and stairs, shoulder the viaduct, cutting it off from horizontal ground constraint and protecting it from a damaging quake. Provisions for local bat populations included dedicated roosting habitats.

Measure 4: Design for Water

Environmentally responsible work in and over the Los Angeles River and air and water quality control was an important aspect of the project. The contractor restricted the amount of construction equipment in the river basin. And when river flow increased, which happened each time it rained, crews evacuated the urban waterway, so no equipment or materials could be washed downstream into the ocean. When evacuations were necessary, the project team had proactively prepared workarounds to ensure the project would move ahead to meet its milestones.

Measure 5: Design for Economy

Socially, the new multimodal viaduct is a unifier. Beyond safely bridging points across the river, it has bridged communities. It restores an essential urban transportation corridor that connects the Arts District with the historic Boyle Heights neighborhood, bringing unity and transportation equity to one of the nation’s largest cities. Recognizing the importance of bringing communities together, the design includes a special loading case for pedestrians. When closed to vehicular traffic, the bridge deck instantly transforms into a spectacular outdoor civic event space for citywide parades and celebrations.

Measure 6: Design for Energy

Linear LED lights are built above and below the deck into the traffic barriers, providing low-to-the-ground street and pedestrian lighting, adding to the drama of crossing the bridge and giving the viaduct its name, Ribbon of Light. Accent lighting from below the deck illuminates the undersides of the arches. The bridge, visible from many parts of the city, will have the ability to be illuminated as a civic beacon.

Measure 7: Design for Well-Being

At its heart, the design promotes resident safety. It is 40 feet wider than its predecessor, carries four vehicular lanes, and features protected 10-foot-wide Class IV bike lanes and 8- to 14-foot-wide pedestrian walkways on each side. The project provides residents safe, direct access to the future 12-acre park planned underneath the viaduct, a first for Los Angeles. Five sets of stairs, perfectly supported by the arch ribs, and two bike ramps provide safe direct passage from the bridge deck to the PARC. The 4-level, 45-foot-tall helical east bike ramp makes the structure accessible to all.

Measure 8: Design for Resources

The viaduct’s 10 pairs of arches are constructed segmentally, the deck has an efficient, thin profile. Foundations at each pier are nearly identical, improving efficiency. The project was cast-in-place, and concrete was sourced locally.

Measure 9: Design for Change

The structure advances the field of seismic bridge engineering with a series of innovations. Designed to remain undamaged and operational after a seismic event with a 1,000-year return period, the viaduct is believed to be the world’s longest, seismically isolated concrete tied arch bridge. It features the first U.S. application of seismic isolators within the verticality of a bent, the world’s first next-generation triple-pendulum friction bearings modified to stiffen after a predetermined displacement and activate a secondary seismic resisting system, the first U.S. bridge to use DSI manufactured multistrand post-tension couplers and Caltrans’ first use of grade 80-ksi concrete reinforcement.

Measure 10: Design for Discovery

The BOE strengthened its relationship with the Los Angeles community and promoted goodwill with a strategic, inclusive community engagement process that began with the international design competition in 2012. The winning concept was based on extensive LA resident input through a series of public meetings and chosen by a panel of members from the BOE, with unanimous support from the Design Aesthetic Advisory Committee, a group of professional engineers, architects, urban planners, residents of the surrounding neighborhoods, local business representatives and river advocates.