Michael Maltzan Architecture’s graceful arches crown new Sixth Street Viaduct

What does it mean to replace an emblematic piece of urban infrastructure, whose presence has ingrained itself into the image of a city and many of its depictions in popular culture over nearly a century? On being enlisted to replace the iconic Sixth Street Viaduct in Los Angeles, USA, local firm Michael Maltzan Architecture had the task of designing the successor to a beloved feature of the city. The structure in question had served as a backdrop for a plethora of instantly recognisable scenes from film, television, and music videos throughout the years, and was indelibly tied to the urban identity of Los Angeles. Built in 1932, the original viaduct had developed several issues over the course of its almost nine-decade-long lifetime, with unsuccessful attempts at preservation ultimately culminating in a move for its closure and demolition back in 2016.

The deterioration of the former viaduct was often attributed to the concrete mixture used in its construction, which made use of sand harvested locally from the Los Angeles River. As the architects explain in a statement, “Unfortunately, the materials in the concrete gave rise to an alkali-silica reaction, which made the structure deteriorate within 20 years of completion. Over time, various costly and ultimately unsuccessful methods were tried to save the viaduct. Seismic studies eventually concluded that the viaduct would be highly vulnerable to failure in a major earthquake and would have to be replaced.”

Bridging the Arts District on the city's west side and Boyle Heights on its east, the viaduct was one of 14 historically eminent crossings over the Los Angeles River, and said to be the longest of them. Among its most identifiable features were a pair of arches that soared over the Los Angeles River section. Adopting these elements as the primary precedent for their design, the team at Michael Maltzan Architecture in association with engineering firm HNTB devised a new 3,500 ft tied arch structure which channelled the image of its predecessor to striking effect.

American infrastructure design firm HNTB was also part of the team selected to undertake the commission, said to be the largest bridge project in the city’s history, following an international architecture competition. The competition was conducted by the City of Los Angeles' Bureau of Engineering, under the leadership of City Engineer Gary Lee Moore, as well as a nine-member Design Aesthetics Advisory Committee. The firm also showcased a display of the bridge’s design during the 17^th Venice Architecture Biennale, in response to the thematic question: "How Will We Live Together", posed by the event’s curator Hashim Sarkis.

Following a five-year construction period that commenced in 2017, the new concrete and steel structure - dubbed the 'Ribbon of Light' on its completion - features 10 pairs of swooping, sculptural arches, with the tallest set among them placed atop the stretch passing over the LA River, evoking the image of the earlier viaduct. Michael Maltzan Architecture notes, "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 connectivity of a civic structure." The new bridge design spans over the LA River, 18 railroad tracks, the 101 Freeway, and several other surface roads in the city.

Serving as a gateway on the east, another pair of arches, immense in their scale, complete the procession of these elements along the edges of the structure's carriageway. The arches themselves skew outwards by nine degrees from the edges of the 100-feet wide structure, whose path through the urban landscape of Los Angeles curves along a 5,000-feet radius. As per the architects, the rhythm of elements frames a sequence of views of the cityscape, which engender an almost 'cinematic' experience - leaning into the old viaduct’s prominence in on-screen portrayals of Los Angeles. These frames have been likened to those seen in a film, where each captures a candid snapshot of the city in all its beauty, chaos, and complexity.

While the average spans between the arches extend for 200 feet, the longest section over the rail lines stretches for approximately 250 feet. Rising around 63 feet along its length from west to east, the viaduct maintains a width of 100 feet over its course. As in the case of its forerunner, the structure accommodates vehicles and pedestrians, with the new inclusions of 10-foot bike lanes and 8-foot sidewalks that expand to 14-feet at unsupported intervals between arches. In order to withstand the region's susceptibility to earthquakes, the viaduct is settled on 32 seismic base isolators equipped with triple friction pendulum bearings at its 23 columns and abutments. This configuration allows the structure to to move up to 30 inches independently in situations involving seismic activity.

Lighting design plays a key role in the project, and is effectively the source of its unofficial moniker as the 'Ribbon of Light' bridge. Above and below the deck, linear LED lights embedded into the viaduct’s traffic barriers offer street-level and pedestrian lighting that contributes to the immersive spectacle of crossing over it. Furthermore, the undersides of the arches are illuminated from below the deck by accent lights incorporated into the structure. "The bridge, visible from many parts of the city, will have the ability to be illuminated as a civic beacon," reflects the firm.

Providing connectivity to areas of interest throughout its span, the structure hosts four sets of stairs connecting the carriageway to the east of the Los Angeles River. In addition, the viaduct’s span also hosts a staircase linked to the arts plaza along the west, as well as paper clip-shaped and helical ramps for further connectivity to the urban realm below. In the wake of the viaduct’s completion, the site below it is expected to become home to a 12-acre public park designed by Hargreaves/Jones Associates, accessible from the elevated deck through a helical bike ramp. Titled 'PARC' (for Parks, Arts, River, and Connectivity Improvement), the urban development scheme will integrate opportunities for sports, recreational programs, performances, and public art initiatives for neighbouring communities.

Having opened to the public on July 9, 2022, the Sixth Street Viaduct is a welcome new update to a city icon - whose unfortunate demise leaves behind a legacy that will be difficult to match. Featuring all the iconic qualities of the original viaduct, albeit, updated with a touch that firmly grounds it in its own time, the new structure has already garnered a generous share of the global spotlight, and in an ideal scenario, may become as emblematic of Los Angeles’ urbanscape as its predecessor.

Project Details

Name: Sixth Street Viaduct
Location: Los Angeles, USA
Year of Completion: 2022
Bridge Design Architect: Michael Maltzan Architecture, Inc.
Architect of Record: HNTB
Project Team: Michael Maltzan (FAIA, Design Principal), Tim Williams (Managing Principal), Paul Stoelting (Project Manager), Matthew Austin, Deysi Blanco, Casey Beinto, William Carson, Scott Carter, Lord Ceniza, Roger Cortes, Michael Faciejew, Mehr Khanpour, Yu Li, Ann Soo, Jose Thomas, Hiroshi Tokumaru, Gee--‐Ghid Tse, Jennifer Wu
Landscape Architect: Hargreaves/Jones Associates
Urban Planning Consultant: AC Martin