Como predicaba Jane Jacobs, las autopistas de gran escala, parques y grandes edificios pueden todos dividir comunidades, desalentando la vida callejera y chuparse la vida de nuestras ciudades.
As with much urbanist lingo, we look to Jane Jacobs for its coinage. In Death and Life of American Cities, she dedicated an entire chapter to “The Curse of Border Vacuums.” Here’s the Jane-splain on what a border does:
A border—the perimeter of a single massive or stretched-out use of territory—forms the edge of an area of ‘ordinary’ city. Often borders are thought of as passive objects, or matter-of-factly just as edges. However, a border exerts an active influence.
While some borders have a beneficial effect of intensifying density, other features of the urban landscape can cut off and constrain neighborhoods that would otherwise grow. It’s not as much about the lines that are drawn, it’s the void they produce with dead-end city streets and thus a border vacuum.
Jacobs outlines a wide variety of borders that produce these vacuums. Transportation infrastructure (roads and railroad tracks) are prime offenders, as are certain kinds of buildings, like large office and housing blocks or sports stadiums. Other vacuum-generators are wide-open public spaces like parks or waterfronts, which can transform the space around them in a way that discourages pedestrians from spending time on the street at various times of day. That promotes vacancy and urban decay.
The Embarcadero Freeway: A border vacuum case study
The story of interstates and freeways slicing up cities, producing segregated urban enclaves is well documented in urbanist lore. Department of Transportation Secretary Anthony Foxx described last year how the interstates in Charlotte made his family feel cut off from the rest of the city.
It makes sense that multi-lane highway would be too tough to cross. But roads not only create a barrier—they can also produce a vacuum that leaves unused space. To demonstrate, look to the example of the Embarcadero Freeway in San Francisco. Even when a road is elevated and possible to cross, it can obstruct public use of a space, in this case the Embarcadero Waterfront.
In the photo above you can see how the elevated freeway cuts in front of the historic Ferry Building, at the end of Market Street. (The area’s early alignment can be seen the film “A Trip Down Market Street” from 1906.) In 1958, the Embarcadero Freeway was built, blocking that section of the waterfront (where it became a favorite Hollywood car chase scene location).
While waterfronts are a common natural border for a city, the Embarcadero Freeway provides a telling experiment in the mixed use of a space. Ports draw in specific uses—such as fishing, ferries, or freight—but they can also work as an amenity, luring residents or tourists to visit. But that was not going to happen when this was the view that greeted people heading towards the Ferry Building.
Much of Jacobs’ criticism of urban planning comes from how top-down views from maps obscure how people use spaces. The alignment of the waterfront and freeway look neat and parallel on paper, but the view above was what greeted people trying to walk toward the historic Ferry Building. Even green space doesn’t bring people any closer to crossing underneath the freeway to the Ferry Building. Compare that to what the waterfront looked like after earthquake damage in 1989 led to the 1991 demolition of the Freeway.
Today, the Embarcadero Waterfront is a thriving pedestrian plaza with shopping, a streetcar, and a view of the bay. It demonstrates that a road or other obstruction not only can create a physical border, but it also produces empty, unusable space that deters pedestrians, even if it’s possible for them to cross.
Why empty space puts people on edge
Border vacuums might best be explained by what is absent—small urban spaces with porous edges where people spend time throughout the day.
Jacobs’ theory explicitly builds on Kevin Lynch’s Image of the City, where she quotes his definition of an edge:
An edge may be more than simply a dominant barrier, if some visual or motion penetration is allowed through it—if it is, as it were, structured to some depth with the regions on either side. It then becomes a seam rather than a barrier, a line of exchange along which two areas are sewn together.
Even a street with scattered border features can survive small spots of urban blight so long as people can move freely amidst small city blocks on narrow streets. A border vacuum emerges when some kind of barrier seals what otherwise be accessible space to pedestrians. Ideally, parks need to beaccessed from multiple directions to succeed.
Building on Jacobs’ work, Marc Szarkowski, a planner who works with the Maryland Transit Administration, wrote a thorough rundown for Better! Cities & Towns in 2013 on the consequences of the many border vacuums found in Baltimore. In a parallel to the Embarcadero, he also points to one that didn’t get built: a proposed highway along Baltimore’s waterfront that was abandoned after fierce community opposition in the 1960s. Had it been built, the city’s marquee tourist attraction, the Inner Harbor, would not have emerged in the 1970s.
“Even the old phrase ‘the other side of the tracks’ originates from our unconscious realization that transportation corridors tended to create scars of decay,” Szarkowski tells CityLab. Poor planning can produce “the separation of economies and divergence of fortunes between communities.”
In many ways, Szarkowski says border vacuums still aren’t considered an orthodox planning consideration.
“Most planners don’t see border vacuums as a problem, attributing their symptoms to other notions.” Szarkowski says. “If a planner still believes that a city is merely a collection of ‘villages,’ then it’s very appealing to physically separate those villages with discrete, destructively-tidy divisions of one kind or another.”
Szarkowski isn’t one of those planners: He wrote a 10-part series on border vacuums, detailing the variety of urban features that can produce them. Roads and railroad tracks are the most common examples; in addition to highways, vacuum-inducing transportation infrastructure includes parking lots, arterial roads, sunken and elevated corridors, all of which all tend to produce wasted space that seals off pedestrians.
A host of architectural and urban features can create the same kinds of vacuums. Szarkowski points to housing/retail/office complexes, superblocks,college campuses, or congregation spaces like stadiums and auditoriums that can suck out all other space for development. Again, the top-down approach cannot demonstrate what you can easily observe on the ground, and the dogma of multi-use development becomes more understandable when places are poorly filled with single-use spaces. Put up a big-box store, a glitzy mega-office complex, or a high-rise apartment building and they can create monotonous blocks of blank walls that discourage people from walking.
As Jacobs put it, “Almost nobody travels willingly from sameness to sameness and repetition to repetition, even if the physical effort required is trivial.” But pepper a sidewalk with multi-purpose distractions and little cross-streets, and the street comes alive.
In Death and Life, Jacobs points to Central Park as an example of a place that could have become a border vacuum if big buildings or wide streets had lined its edges. (Michael Minn has a good analysis of what Jacobs got right and wrong about that space.) But little things can add up to combat big borders, as Jacobs lists the numerous activities that fill the park with diverse distractions, giving it multiple uses and openness to combat the vacuum.
Decades later, Jacobs’ thinking held up. William H. Whyte’s classic 1980 urbanist documentary The Social Life of Small Urban Spaces used time-lapse cameras to demonstrate how people use parks in New York. His film speaks to the same truth—the smallest observations of people can tell us big things about what works in a city. To transform a border vacuum into a seamless and vibrant public space, just take a look at it from street level.