As cities and states enact stay-at-home orders to stem the COVID-19 outbreak, once-packed urban streets are now empty of cars.

Some mayors have seized that opportunity to open the pavement up to people for exercise. New York City Mayor Bill de Blasio said last week he would open a limited number of streets to pedestrians as an alternative to crowded parks, and in Philadelphia, a stretch of MLK Drive has been shut off to traffic in favor of bicyclists.

To some advocates, the street closures are a silver lining to the public health crisis: a chance to see what urban streets can do without cars on them. It could even lend more momentum to the car-free streets movement that has grown since San Francisco officially remade Market Street into a pedestrian promenade in January, inspiring cities like New York and Denver to experiment with the concept.

Pedestrian-focused street design has long been a staple in European cities, but experts say implementing such a change in the U.S. requires factors that don’t always exist in its car-centric cities. Jason Thompson, a senior research fellow at the University of Melbourne, recently analyzed the design of 1,700 cities and found the U.S. tended to have sparser road networks with less transit — conditions that do not lend themselves to car-free streets.

"They also work best in 'compact' cities where lots of people live nearby in medium to high-density apartments and are able to make more frequent, smaller purchases for their daily living," Thompson told Smart Cities Dive in an email. "There are sections … of cities that lend themselves to car-free streets, but they are overwhelmingly in inner-urban areas that make up a tiny proportion of the overall land-mass."

How can U.S. cities better position themselves for car-free streets? Creating such environments can mean infrastructure changes to physically transform the pavement and implement forward-thinking dynamic designs. But most of all, it means a mindset shift.

“It requires thinking that we’re not just moving vehicles, but moving people," Elizabeth Deakin, professor emerita of city and regional planning at the University of California, Berkeley, told Smart Cities Dive. "It changes the calculus, you start to think more about safety and public health in how policies are done. With changing generations and changing mixes of training, we have more people realizing that these options exist."

How San Francisco made it work

The idea of making Market Street more pedestrian friendly had been kicking around San Francisco for decades, but started picking up steam in 2009 when the city began exploring how to reshape the corridor, which runs through the center of the city. 

Geeti Silwal, an urban planner with the firm Perkins and Will and a key planner on the Market Street project, said the initial goal was not to remove cars entirely, but rather minimize their right of way to create something like a "promenade where people want to stroll and take in the whole city."

"We were thinking how to make sure this is a place that is loved and is a destination," Silwal told Smart Cities Dive. "We were looking at how to minimize carbon intensive modes, prioritize pedestrians and have a wider public area."

Because Market Street is a main artery, there was concern that limiting car traffic could create congestion elsewhere. The city ran experiments, creating trial traffic diversions and parceling out more bike infrastructure to see how citizens reacted. Those experiments made clear that a car-free environment could work, and in 2017 San Francisco announced plans to shut off a two-mile stretch of the street to all but commercial vehicles, TNCs and transit.

However, it’s not as easy as blocking of the cars. Making a truly pedestrian-friendly space on Market Street required sidewalk expansions, transit redesigns and installations of public art. Buses and streetcars were moved to the center lanes, and the bike lane was widened and cordoned off with benches and railings. The city integrated new trees and biodiversity, as well as furniture that could create a unified design. Even sightlines were rethought to improve wayfinding, Silwal said.

"We were thinking of how to make this street kind of a living room and a place people would enjoy," she said. Already, multimodal ridership has increased; the San Francisco Municipal Transportation Agency found bike ridership on the corridor jumped 20% the day after cars were off the street, and Populus reported that ridership of Spin scooters was up 30% in the first month of Market Street being car-free.

Elsewhere, Denver Mayor Michael Hancock recently announced a portion of a downtown street in front of City Hall would be shut off to cars starting in May. The redesigned Bannock Street, Hancock said, "expands a civic space we are already very proud of into a more welcoming gathering place for generations to come."

Even though that small stretch of the street already sits next to a public park and is frequently shut down for civic events, the city still had to do extensive analysis to study how traffic would be impacted by a permanent closure. Jennifer Hillhouse, director of transportation and mobility planning for the Denver Department of Transportation and Infrastructure, said the city decided there were enough alternatives to not add to congestion.

Now the city is exploring how to signal to residents that this is more than a traditional street. In the short term, that will mean new planters and public art, as well as new striping on the pavement, but the city is also soliciting ideas for a long-term vision that will reconstruct the space — ideas that could be used elsewhere in the city. 

"We're working to transform our streets to reduce conflict," Hillhouse said. That's included bumping out curbs on some busy streets and reducing left turns in some areas to make them more pedestrian friendly. "It presents a lot of opportunity to think about streets for people and not just for cars."

When cars come back

The failure of some pedestrian-only areas in the U.S. shows the limits to the philosophy.

In 2016, Fresno, CA shut down its Fulton Street pedestrian mall, removing the fountains and benches designed for shoppers. In that same year, Buffalo, NY revived its Main Street neighborhood by restoring traffic to some areas. Even with slow speeds (cars are limited to 15 mph) and some portions still being shut off to traffic, Mayor Byron Brown said "we are seeing Main Street rise again" because of the cars, according to the Buffalo News. 

In both cities, the pedestrian malls had been notoriously vast and empty, rather than feeling like vibrant corridors. It’s a sign that not every street can be comfortably transformed, especially wide, high-speed streets that haven’t traditionally been friendly to pedestrians. 

Thompson of the University of Melbourne said businesses and housing also determine whether a car-free environment can succeed. It helps to have an "interesting" street, and retailers that are "generally boutique or smaller versions of bigger retail stores where people expect to be able to walk / ride home with their purchases and not load 100 lbs of furniture or groceries home again."

Dynamic pavement creates new possibilities

Looking forward, some planners think any block could go car-free with just the flip of a switch. Sidewalk Labs, Alphabet’s urban innovation offshoot, has pitched a set of design principles that would reimagine streets for a multimodal future, tailoring different streets for different modes. 

Under this vision, there would be four types of streets: "laneways" that serve pedestrians; "accessways" with a speed limit of 14 mph designed for cyclists; "transitways" that include buses and trains; and “boulevards" that would accommodate cars. The fastest streets for cars would largely be on the outside of urban centers, with cars only traveling down slower-speed streets when necessary. 

That, said Sidewalk Labs mobility lead Willa Ng, is a shift from a mindset that "every street should be as fast as possible," which is unsafe and an inefficient use of space.

“We generally think of streets by protecting modes from each other. We put up a barrier of parked cars, of curbs, of bollards to protect bikes from cars,” Ng told Smart Cities Dive. Her approach imagines "a hierarchy of speeds."

Acknowledging the infrastructure challenges that come with redesigning streets, Sidewalk Labs has looked for more dynamic technology. The company has partnered with French civil engineering firm Colas on a dynamic pavement that would use slabs with embedded LED lights to signal road use. 

For example, a street could be designed for cars during rush hour, but by simply switching the light signals, the pavement could be converted into a pedestrian alley. Likewise, sidewalk space could be temporarily designated as a pickup and dropoff zone with lighting cues. 

It’s a way to reclaim street space for different modes without the massive infrastructure changes that would come from expanding curbs or building new bike lanes. The model will be tested in Sidewalk Labs' Quayside development in Toronto, and Ng said there’s been interest in trying it in smaller private developments. Models have shown that the approach could even ease traffic for individual drivers.

It's emblematic of a broader mindset shift that sees planners rethinking whether streets and avenues could be designed for people rather than vehicles. The aftermath of the COVID-19 pandemic could allow cities to rethink transit and infrastructure more broadly, and the popularity of car-free streets in some cities could raise their profile. 

"I do think Broadway in New York and Market Street are setting a precedent. If San Francisco can do it, should we do it?" Silwal said. "More and more there is a school of thought of let’s get this right, for streets that are about people and about connections."