August 2, 2022
Bridging the Divide Between the Possible and the Impossible
The viaduct—it mostly crosses land not water—runs 3,500 feet, linking the eastern edge of downtown Los Angeles to the palisades of Boyle Heights, one of the city’s oldest neighborhoods, and home to generations of Latinx families, as well as recent immigrants. The 100-foot-wide structure hopscotches a riparian littoral, entirely remade into a plain of warehouses, cold-storage plants, metal fabricators, railroad tracks, rainwater run-off culverts, tire-retreaders, power lines, and a six-lane freeway. The new viaduct has ten pairs of arches that lean outward from the road deck, gesturing toward the somewhat bleak landscape immediately below, but also framing panoramas of downtown’s skyline and the hills beyond. One can peer through the 300-foot-long arches to watch trains chug to and from Union Station, follow the trickles of water dripping into the concrete river channel, absorb the continuous roar of cars speeding down the highway, or just ponder the in-between space such a long span provides. In a sense, the 6th Street Bridge reflects the zeitgeist of modern Los Angeles. As Michael Maltzan, the bridge’s architect (working with a design team that included HNTB, Hargreaves Jones, and AC Martin) says, the design “preserves directness. Its ambition is to prove that infrastructure can be extremely ambitious in its form and still be infrastructure left in a natural state. It doesn’t have to be rarified.”
There was no alternative to replacing the 1932 viaduct, which suffered from a form of “concrete cancer.” The aggregate used in the concrete had caused a chemical reaction known as Alkali Silica Reaction. Twenty years after the bridge was completed it was already decomposing. The new viaduct, the largest bridge undertaking in the city’s history, cost $588 million dollars and took nineteen years to complete, arriving three years late and costing $100 million more than originally expected. It has ten sets of arches—echoes of the original bridge’s pair of steel truss arches—with seven sets 30 feet high, two 40 feet, and two 60 feet. The cables supporting the roadway had to be tensioned like tuning the strings on a violin, over and over, until they reached equilibrium. Construction consumed 27 million pounds of falsework and required liquid nitrogen to cool the concrete as it was being poured, to prevent the curing concrete from overheating and become a welter of cracks. Deceptively simple looking, the bridge is an engineering feat, resting on a set of base isolators—massive friction-pendulum bearings that isolate the bridge from the ground upon which it rests. In an earthquake the bridge will wobble independently, then the bearings will settle into their original positions, stabilizing the massive structure. The viaduct is believed to be the only bridge in the world designed to handle seismic forces greater than required by code: a 1,000-year event of magnitude 9.
The viaduct is more than a roadway in one other key respect. The space below will be a 12-acre public park and arts plaza when its landscaping is completed by the end of 2025. Underneath will assume as much importance as up above—perhaps more to the locals who, it is hoped, will adopt the greenfield and its playgrounds as their own. This will not be an uncomplicated future, however. Already, city officials have had to close the bridge to car traffic because, as elsewhere in Los Angeles, posses of drivers have etched burnt rubber cycles into the pristine concrete and taggers have graffitied the arches. Several critics, meanwhile, have suggested making the bridge pedestrian-only.
Metropolis spoke with Deborah Weintraub and Michael Maltzan about the viaduct. Weintraub is Chief Deputy City Engineer for the Los Angeles Bureau of Engineering and the highest-ranking architect in the City of Los Angeles. She spearheaded the city’s effort to build a new bridge that would be not only functional and beautiful, but become a public space in its own right. Los Angeles-based Maltzan is known for his museums, civic and urban designs, and his commitment to livable housing for the homeless.
Greg Goldin: You’ve just completed the most expensive bridge in the city’s history. Usually, people think of infrastructure, especially in Los Angeles, as characterless, mundane. You’ve managed a bridge that is anything but routine, and seems already to have captured the city’s imagination. How’d you pull this off?
Deborah Weintraub: Thinking about making a bridge something more than basic infrastructure happened a long time ago. It began nineteen years ago. The discussion then was: Is there a way to preserve the much-beloved historic bridge, which was suffering from alkali silica reaction? Experts from all over the world concluded there wasn’t. So, ten years ago we held an International Design Competition that would think about how a new span would impact the city and the neighborhoods it was going to cross over and touch down in. We wanted to know what the bridge would look like from underneath and from a distance, but we also wanted to know what it would be like to traverse it, and what it could offer to communities on the spaces underneath it. We tried to reframe the discussion so that it was about infrastructure, architecture, and community.
GG: This was not a universally accepted view in the city at the time. There was considerable opposition to tearing the bridge down. Wouldn’t it have been cheaper and easier to capitulate and preserve the old bridge?
DW: That certainly was what opponents wanted. The city’s Cultural Heritage Commission and some members of the city council said, “Okay, yes, alkali silica reaction is seismically unsafe. But let’s just rebuild the old bridge [as it was.]”
GG: They wanted a new bridge to be a carbon copy of the old one?
DW: Yes. But then we held a council hearing and architects from across the city spoke to the importance of doing something of our moment, of our time, using concrete – to join the suite of the remaining bridges across the river. It was pivotal to have the architecture community speak forcefully. The then-mayor, Antonio Villaraigosa, got very much behind the idea of the International Design Competition, which put design and architecture in the foreground.
GG: Wasn’t there something that nevertheless resonated from the plea to preserve the 6th Street Bridge? As you know, the 6th Street Bridge was iconic. It was well-loved. The double-set of riveted, slouching arches, spanning the concrete-enclosed Los Angeles River, somehow embodied the gritty, un-Hollywood spirit of Los Angeles. Did the sense that the old bridge somehow was a paean to the real city help create a mandate to build a new monument to Los Angeles?
Michael Maltzan: Clearly, the old bridge captured some part of the city’s ongoing identity. It was certainly connected to the past and to the suite of concrete bridges built by Merrill Butler [L.A.’s longtime Engineer for Bridges and Structures, who built nine concrete-arch bridges over the Los Angeles River between 1923 and 1933] up and down the river. It had a life that was greater than the basic, pragmatic role of a bridge. So, the role of the old bridge meant that the new bridge also had to project an identity around the future of the city as well as the past.
DW: Absolutely. Merrill Butler’s bridges were the precedent for making the new bridge a landmark. Taking down a much-beloved concrete bridge led directly to building a new concrete bridge that demonstrates the concrete technology of our time.
MM: But much of our work was trying to find the right connection between what the bridge would represent locally to its neighbors and what it stood for in the city at large. The two goals – citywide and street level – don’t naturally align. Our answer was to connect in some way to the history of the Sixth Street Viaduct and what that bridge meant to the community. We did that by taking the original arches of the Merrill Butler bridge and amplifying and multiplying them, so those arches became the major thematic element of the bridge as a whole.
GG: Right. There’s the bridge as you see it from afar and there’s also the bridge you experience if you drive or walk across it. It’s a sequence of open, differently-sized arches, framing all kinds of city views. But then, because the space beneath the bridge will become a park, you created ramps that allow someone to walk from the deck to the space beneath.
DW: We spent $100 million acquiring the ground beneath the bridge, and Michael took the mandate to get you from above to below, and created the corkscrew ramp and the paperclip ramp [a 790-foot-long spiral and a 640-foot-long switchback], pedestrian and bikeways that cross under the bridge, which give you the fantastic experience of being close to this massive piece of infrastructure. That, by the way, was a hurdle. I remember talking with Caltrans [California Department of Transportation, which helped fund the project]. They looked at that and said, “Isn’t there another way to do this?” And I said, “No, no. This is the only way to do this.” This was about beauty, and it is beautiful.
GG: It’s not just beautiful, it’s exciting. We rarely get to crawl underneath bridges.
MM: This is one of the places where I think the different disciplines of architecture and engineering really connected. Those ramps are of course creating accessibility. But they also create a different type of access. You’re able to experience the full weight and the thrill of this structure being very close to you physically. You’re able to get very close; to almost feel like you are touching engineering and infrastructure and something that is big and monumental and iconic.
GG: You’ve also made the base isolators, which allow the bridge to sway thirty inches in any direction in an earthquake, part of the ground show.
MM: We’re continuing to work to make those seismic bearings visible and to allow them to remain exposed in places, because they’re a huge part of the story. They may be very pragmatic at one level. They are about an engineering response to the inevitable earthquakes we have in Southern California. But they’re incredibly interesting things at a scale that you rarely get to see. That potential to pull back the curtain a bit and to see and touch and experience something at this scale – to experience infrastructure at this level – I hope becomes something that helps to cement a personal connection between people and the bridge. It may seem strange to believe that you might have a personal connection to something that’s so big, but I think that’s where structures at times start to take on the more iconographic characteristic of a city. It’s because individuals get to somehow make it their own. It gets woven into their own personal story. And of course, it’s everybody’s hope that the bridge will have that kind of life.
GG: I know this is an enormously complex project but what was its most difficult aspect?
MM: We literally had to find places for the bridge to touch down all the way across the full length of the site. You’re crossing multiple rail lines, you’re crossing the L.A. river, which is controlled by the U.S. Army Corps of Engineers. We had to coordinate with power lines that run over the bridge. We cross a highway as well as a number of city streets. We bisect and span all kinds of other utilities. I began to say the bridge was like an actual cross-section of the full complexity of the city at a political, social, and economic level. That was a challenge in and of itself.
GG: Which leads me to ask, was there a specific moment when, in dealing with so many different agencies, each with a say in the design process, when you had to say, no, we will not yield? This is a make-it-or-break it part of the design?
MM: Naturally, there were any number of them, but the one I think of most is the street lighting.
GG: That’s not something one would immediately think of.
MM: The city’s street lighting bureau was insisting that the lighting of the bridge would be accomplished with a series of standard city light poles that would march down the bridge. We were totally opposed to that. We didn’t want a series of poles that would be visually obtrusive; we wanted the arches to remain aesthetically pure, which would be more in keeping with the simple, plain-speaking spirit of the bridge as a whole. We wanted lighting to wash the deck rather than illuminate it from above. We weren’t just concerned about visual clutter. We didn’t want people walking across the bridge to feel as if they were under surveillance, or trapped in a corridor of street lamps. We were trying to make the bridge deck into a place, somewhere that wasn’t just a conduit or vestibule that could get you from here to there, but a place that you could really occupy.
DW: We had to build a mockup of Michael’s lighting design, and demonstrate it. And, still, after that, the Bureau of Street Lighting called me in and said, “We still want to put the poles on.” And I said, “Not over my dead body.” That certainly wasn’t resolved in one meeting!
GG: That brings me back to my earlier question. The bridge spans a spot on the eastern edge of downtown that’s essentially industrial and, frankly, the opposite of beautiful. Wouldn’t it have been simpler to build a typical freeway overpass-type bridge?
MM: You’re spending significant taxpayers dollars on infrastructure of this kind. The idea that we wouldn’t demand that it do as much as possible – that it do more than what most highway overpasses do…we need to change that attitude.
DW: I think we tend to silo the disciplines of engineering and design. And it’s to our detriment. With Merrill Butler, every bridge was different; each had a different aesthetic and each explored what concrete form work and concrete shapes could do. I think we should see this new bridge as an avatar of the potential for that kind of integrated thinking. And for the value of beauty.
MM: We should remember that the Merrill Butler was influenced by the City Beautiful movement, and that moment passed. That tells you that it’s not automatic, it’s not inevitable. It’s worth keeping in mind now that the visionary thinking behind the 6th Street Viaduct, as Deborah was saying earlier, stretches back nineteen years. It’s easy to think we solved the problem this afternoon. But I think one of the great takeaways of what’s been accomplished here is it’s not only a two-decade-long process but one where individuals in the city, from people in the Bureau of Engineering all the way up to the mayor, set the bar for a level of ambition for the city in the future. And when they did, it was a long way away.
GG: We began this conversation with the notion that infrastructure is now more than a concrete span permitting cars to get from one side of a city to another. I know in your view this bridge is not just a bridge.
DW: Well, here’s one example. Three years from now, the park beneath the bridge will be open. And kids from Boyle Heights will play their soccer tournaments under the bridge, using the shade of the bridge to provide some relief from the sun. As Michael said, it’ll be part of their lives. So, it’s more than a bridge.
MM: I think that’s huge. To my mind, we’ve accomplished a huge first step by opening the bridge, but the parks and the public spaces on both sides below are absolutely key. The goal of the bridge is to weave multiple lives of this part of the city together. And that park is not an extra, it’s absolutely essential, absolutely integral to the overall vision of what the bridge project is.
DW: I would also add one more thing. The original concept that Michael and HNTB had for this series of arches and a cable stay system to support the roadbed, have allowed the roadbed to be very slender. The arch system and the cables are also engineering feats that give the distinct shape to the entire bridge. And I’d be remiss not to add one more thing, because it’s important to me. This was a team who built this bridge led by a woman, largely female with a female construction engineer there the whole time. I don’t know of any other infrastructure project in the world that’s been led predominantly by women at this scale. And that’s important to me. Just to deliver it, to get it built, to deliver.
MM: I think, in some sense, that’s the real story we’re telling here. As a culture, I think we think about the complexities, the number of people who have to be involved in something like this, and we throw up our hands and we say, “it’s impossible. We need a benevolent dictator to make these things happen.” But that’s exactly the beauty, the power of infrastructure. It does take so many people. It is the result of the broadest and most extraordinary group of individuals that have to come together to make this happen. It is the result of many, many people. And that maybe is the most important story of all, especially at a moment like today.
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- AC Martin
- Deborah Weintraub
- Greg Goldin
- Hargreaves Associates
- Iwan Baan
- Los Angeles
- Michael Maltzan
- Sixth Street Viaduct
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