Sixth Street Bridge is falling down. Also known as the Sixth Street Viaduct, it’s a Los Angeles icon that millions have seen and probably didn’t even notice. The 3,500 ft. four-lane overpass that runs from the LA Arts District east to Boyle Heights has been featured in countless films, commercials, and music videos since first being constructed in 1932. The structure crosses literal and figurative barriers, embodies a spirit of industrial America, and to many locals is considered a source of pride and self-identification. It will soon be replaced.

During construction, an on-site plant was used to supply concrete for the viaduct, and it was discovered in the 1940s that the high alkali levels of the concrete aggregate used in construction were causing a chemical reaction that was weakening and destabilizing the foundation. In an alkali-silica reaction, a gel is produced that absorbs moisture and exerts pressure as it expands, creating cracks when the gel is encased in concrete. Since that initial discovery, the city has spent a lot of time and money trying to save the iconic bridge, including a major retrofitting project in 1995, but in 2004, a series of seismic vulnerability studies revealed that it was the beginning of the end for an icon.

There’s a 70 percent chance of a major earthquake knocking down the Sixth Street Bridge in the next 50 years, and that’s why the city will knock it down themselves later this year. The $400 million replacement project, which will create about 5,000 jobs according to the city, is funded mostly by the Federal Highway Bridge Program and the State Proposition 1B Seismic Safety Retrofit Program. The redesign is led by HNTB, a firm chosen by the city from a pool of nine firms that entered a design competition in 2012. Construction of the bridge is scheduled for completion in 2018, and the new bridge is to open in 2019.

Former Mayor Antonio Villaraigosa emphasized in several speeches how important the bridge is to the city, both for transportation purposes and culturally. But the new bridge, he said, represents the city’s future. Los Angeles has an opportunity to reimagine its identity with the construction of the new Sixth Street Viaduct. The bridge today coexists with many urban elements, and as one city project designer put it, what’s under the bridge is just as important as what’s on top of it.

The Sixth Street Viaduct carries about 13,000 vehicles each day. It crosses 17 railroad tracks owned by five railroad companies, it crosses the Los Angeles River, and it crosses several roadways, including U.S. Highway 101. The bridge crosses under two power line corridors, some of which will need to be moved underground, and abuts with more than two dozen properties, including 15 buildings that will have to be demolished to accommodate the new design.

It’s a huge project involving dozens of government agencies and other interested parties, said Alfred Mata, project manager for the Sixth Street Viaduct. “There’s a lot of work involved with all those aspects and that’s aside from having to design it and manage the overall design of the project and coordination with the city,” he said.

The entire local populace and the community of Boyle Heights, in particular, view the bridge as a community landmark and regional icon, Mata said, but it’s also very important on a practical level. The old bridge will be demolished before the new one is built, so traffic will have to be rerouted. “There’s a limited number of places to cross the river between the Boyle Heights community and Downtown Los Angeles. This makes the Sixth Street Viaduct an important link between those areas and it’s also a busy one,” he said.

Upgrades to about 20 off-site intersections will begin this summer, including repaving, restriping, and modifying or upgrading traffic signals so the routes that will see more traffic over the next few years can be prepared. The temporary changes to local traffic flow are just the beginning, though. The new bridge will change the region’s appearance and city officials hope the new design will transform the community.

The city wanted to keep the parts of the old design that the public loved, Mata said, which is primarily that the bridge was an icon, while also meeting modern urban needs and transforming what the public space is used for. Between 2006 and 2011, more than 50 meetings were held both internally and with the public to guide the thematic direction of the replacement bridge and to establish just what the city was looking for. The international design competition held in 2012 was the city’s attempt to find a design and a firm that could meet all those goals, Mata said, and HNTB’s design succeeded on all counts.

The new bridge is wider, more welcoming, more connected, safer, and will have more amenities, such as wider walkways for pedestrians and bicyclists, Mata said. The old bridge was just 46 feet wide and the road had no shoulder. The new design is also straighter, which will remove the kink found in the old bridge. “There’s going to be some improved connectivity between the bridge deck and the ground beneath it,” Mata said. “Right now, if you get on the bridge, or most bridges, you just have to go from one end to the other. [On the new bridge,] there are going to be some stairs and ramps that connect the bridge deck to the ground beneath.”

It’s common for spaces beneath bridges to be neglected in urban design and as a result those spaces are often aesthetically unappealing. According to the broken windows theory, neglected areas signal to passersby that criminal or anti-social behavior is more acceptable there, which can maintain or escalate crime rates and make a bad situation worse. Looking at the new bridge design holistically was a major consideration for the city and the city’s Department of Cultural Affairs played a role in seeing that the new bridge would be more than just a bridge. Mayor Villaraigosa and City Councilmember Jose Huizar appointed nine community leaders and professionals to a Design Aesthetic Advisory Committee (DAAC) to provide insights on the structure’s aesthetics, associated roadways beneath the structure, and integration of city and community monuments.

Individuals selected for the DAAC include residents of the Arts District, and members of organizations like the UCLA Department of Architecture and Urban Design, the Boyle Heights Chamber of Commerce, design firm Point C, the Boyle Heights Technology Center, Friends of the Los Angeles River, Eric Owen Moss Architects, and Suisman Urban Design. The idea was to include locals who knew about sustainable, modern design and to make sure the new bridge would become a welcoming and accessible place.

In keeping with the old bridge’s design, which features arches over the river crossing, the new bridge features an undulating ribbon of arches of various sizes. The ribbon of arches shows that the bridge connects more than just land from east to west, but also connects multiple levels on a vertical axis, providing people with access to both sides of the river and direct access to the water itself. There will be multiple stairways and ramps down to areas beneath the viaduct, as well as stairs leading up to the top of one or two of the taller arches, providing visitors with a new view of the city.

The creation of a new bridge like the one the city has designed could also lead to new opportunities not yet imagined. There have been talks of new rail stations being built in the Arts District, and one argument supporting such a project is the existence of a community-friendly Sixth Street Viaduct. If the bridge can serve as a community attraction, it would provide an impetus for the development of more projects in the area and more jobs in the community.

The Sixth Street Viaduct is more than 80 years old, so it’s natural that people will miss it. It’s on the National Register of Historic Places. It’s gritty, industrial, and photogenic. At night, the Sixth Street Bridge made the perfect ominous backdrop for the time-traveling robot T-1000 in the 1991 blockbuster Terminator 2, and during the day, the viaduct was the perfect landscape for a car chase or race like the one in Grease. The old viaduct is symbolic of the America of yesteryear – rugged and utilitarian. But that’s quickly eroding, giving way to a new generation of ideals.

Renderings Credit: HNTBThis story was originally published by FutureStructure.com

Colin Wood Colin Wood  |  Staff Writer

Colin has been writing for Government Technology since 2010. He lives in Seattle with his wife and their dog. He can be reached at cwood@govtech.com and on Google+.