Why Speed Kills Cities

Urban speed limits are tumbling.

Urban speed limits are tumbling. Mica Weber/Shutterstock


Connecting state and local government leaders

U.S. cities are dropping urban speed limits in an effort to boost safety and lower crash rates. But the benefits of less-rapid urban mobility don’t end there.

“Slow the hell down.” That’s the message New York City Mayor Bill De Blasio delivered on Twitter as he announced the revival of the city’s speed camera program. The cameras went live in July with expanded hours, issuing hefty tickets to any driver who creeps above 36 miles per hour—that’s 11 mph above the city’s 25 mph posted limit—in 750 school zones throughout the city’s five boroughs.

New York City, which has been struggling to get its Vision Zero safe-streets program back on track after a 2019 surge in cyclist deaths, has also been the most prominent American city to test the idea of a “neighborhood slow zone”—a relatively infrastructure-light path to safer streets that drops speed limits to 20 mph on interior roads in residential areas. It will soon be joined by Philadelphia, where the inaugural designation of two slow-speed corridors, modeled after the New York City program, was overwhelmed with more than two dozen applications.

Elsewhere in the U.S., urban speed limits are tumbling. Portland, Oregon, just wrapped up a campaign installing more than 2,000 new signs to bring residential streets down to 20 mph, along with educational “20 is plenty” signs. After lowering its default speed about two years ago to 25 mph, Boston wants to go further down to 20 mph; Washington, D.C., could follow suit. Imposing tighter limits on leadfoots is a key part of the Vision Zero campaign for reducing traffic deaths and injuries, because of the dramatic safety benefits associated with reducing vehicle velocity.

Does this add up to evidence that fast-paced Americans are ready to embrace the virtues of city life in the slow lane? The case for a fundamentally slower city has gained traction recently, especially in places where the rise of micromobility, the promise of autonomous vehicles, and the very-much-already-here problem of road congestion have converged, slowing drivers to a furious crawl. (The average car in Midtown Manhattan goes 4.7 miles per hour.)

Seeing cities scramble to accommodate shared electric scooters on conventional streets, Gabe Klein, the author of Start Up City, advocated for the idea of urban “slow lanes” in Forbes—non-separated but narrower travel lanes with a 15 mph speed limits that would prioritize non-cars. New York’s Financial District Neighborhood Association suggested the idea of creating an entire Euro-style “slow streets district” in a big chunk of Lower Manhattan, full of wide sidewalks and Dutch-style woonerfs, or shared streets. Others have suggested a wholesale woonerf-ization of the whole Manhattan street grid.

That might sound suspiciously European for a nation that has spent the last half-century-plus plowing high-speed thoroughfares into and around its metro regions. Nationwide, highway speed limits have grown dramatically since OPEC-era federal speed controls—bowing to cheaper gas, pressure from driver lobbying groups, and Sammy Hagar—were fully lifted in 1995. And many big-ticket urban transportation projects are hyped on the promise of trimming travel time, often for a relatively elite class of users: Elon Musk’s “Express Loop” project would would hurtle riders under Chicago at 150 mph (and cost $1 billion) to shave 30 minutes off a downtown-to-airport run, while “flying taxi” promoters can’t stop touting the eye-popping travel times available to future riders of their nonexistent vehicles.

But when the most exciting urban transportation innovation of the decade is cheap little rented vehicle that struggles to hit 15 mph, perhaps it’s time to admit that urban mobility solutions don’t necessarily involve flying taxis or Teslas-in-tubes. The tortoise can win this race.  

The most obvious immediate benefit to a fundamentally slower city is the safety boost it delivers. Reducing speeds is the best, easiest, and fastest way to quickly radically improve safety, for both drivers and anyone in front of them. A recent report from the Insurance Institute for Highway Safety estimates that rising speed limits in the United States have led to an additional estimated 37,000 deaths over the past 25 years. “We know that very small changes in speed can have big consequences for pedestrians,” says Jessica Cicchino, the vice president of research at IIHS. “A pedestrian struck at 25 miles per hour has 25 percent chance of being seriously injured—but that climbs to a 50 percent chance at 33 miles per hour.” Importantly, lower speed limits also reduce the number of crashes, as an IIHS study found last year in Boston after it lowered its default speed in 2017.

Speed kills in a more abstract sense, too. Building urban roads that can handle a large number of vehicles traveling at 35 miles per hour and up means making them wider, with fewer curves. High-speed highways and street-level limited-access urban thoroughfares famously do a host of bad things to those who live nearby or underneath these big hostile barriers. What’s less discussed is what they’re doing to the people inside the cars. In his recent book Building and Dwelling, the planner and urban scholar Richard Sennett writes about how going faster in cities has lead urbanites to value “space” over “place.”

“You move through a space and you dwell in a place,” Sennett told CityLab’s Ian Klaus last year. “It’s a distinction for me that has to do with speed and automobiles. When people start driving at a certain speed, they lose awareness of where they are. … Where this gets reflected in urbanism is the more we create spaces where people move fast, the less they understand about what those spaces are. At about 28 or 30 mph people, moving through an urban environment stop being in a place and are in space instead.”

The time benefits one gets from boosting speeds in urban areas can end up being surprisingly modest: In downtown streets, the difference between a 25 mph commute and 45 mph commute is roughly an addition 48 seconds for every three-quarters of a mile traveled, according to Nelson\Nygaard. It’s also worth remembering that even urban “rapid transit” often isn’t really all that fast. (The New York City subway averages 17 miles per hour.)

When human- or animal-powered urban movement was the norm, there was much less anxiety about losing time in traffic jams, Sennett writes; in the twisted streets of old cities, congestion was accepted as just an fact of life. Only when cities like Paris transitioned from narrow lanes to wide Haussmann-style boulevards did urbanites began to associate speed with freedom of movement—witness reports of widespread road rage that sprouted up in Paris in the 1870s and early 1880s. Urban traffic jams today are a visceral sign that something has gone wrong—the city wasn’t working. Like not being physically touched in public, the desire to move freely—and not be stuck in traffic—is a sensation we take for granted as natural. But it’s a historical construction of our auto-centric sensibilities.

In his prescient 1973 essay, “The Social Ideology of the Motorcar,” André Gorz makes a similar point about how private cars turned speed into a commodity that, when introduced into the city, created havoc: “When everyone claims the right to drive at the privileged speed of the bourgeoisie,” he wrote, “everything comes to a halt, and the speed of city traffic plummets.”

Sennett also uses traffic flows to show the problem of scaling from the local to the urban—a theme in the debate to how to create an “open city.” He compares Lewis Mumford’s top-down garden city urbanism with Jane Jacobs’s bottom-up street-ballet localism. Both Mumfordand Jacobs famously loathed the impact of the automobile, but Mumford argues that you can’t build infrastructure bit-by-bit, the way Jacobs sees the urban fabric: When you’re engineering how to circulate millions of vehicle trips, you have to plan at a bigger scale. By that logic, perhaps urbanists shouldn’t demand slow lanes or slow neighborhoods: They should ask for a slow city.

To get one, simply dropping speed limits isn’t the answer; street design itself—not enforcement or signage—is the most powerful governor of driver behavior. When Streetsblog compared studieslooking at neighborhood slow zones in New York and London, the Big Apple didn’t see a significant drop in injuries, but London enjoyed benefits because they implemented serious traffic-calming infrastructure changes, such as raised crosswalks and street-narrowing curb extensions.

A lot of bike and pedestrian advocates will also argue that Americans are just doing speed limits wrong. Most state DOTs typically follow a rough measure known as the 85th percentile rule. Traffic engineers conduct studies measuring the average speed of drivers on a road, then they set speed limits so that 85 percent of those drivers would be traveling under the speed limit. That idea, as FiveThirtyEight detailed in 2015, effectively sets a minimum speed rather than a maximum. In 2017, the National Transportation Safety Board recommended that the Federal Highway Administration scrap the guideline in favor of other road factors like crash history or pedestrian counts.

Advances in technology might prove to be a key that unlocks the city-healing powers of pokiness. The micromobility revolution not only highlights a burgeoning need for more slow lanes: It can vividly illustrate the people-moving power of very modest speeds. When a dude on a electric scooter that rarely goes over 10 mph handily beats a BMW across town at rush hour, it’s easier to see how the scale of cities supports more-but-slower vehicles.

Another argument for slowness: It could allow autonomous vehicles to actually work without killing us all. If we can reconceptualize autonomous vehicles as low-speed machines trundling around downtown rather than interstate-eating robots tasked with making complex split-second driving decisions at highway velocities, everything gets less difficult. In a way, the robo-shuttles in action in places like Las Vegas and Brooklyn, which operate at speeds under 25 mph, are low-key Trojan Horses for traffic calming. “A lot of the roads where we operate already are in congested places where traffic speeds are already slow,” says Alisyn Malek, the chief operating officer and co-founder of May Mobility, which is operating shuttles in Detroit and Columbus. “If we can use the curiosity and excitement with autonomy to drive goals about pedestrian safety and bike lanes to make cities AV-ready when the time comes, that’s great for everyone.”

Billy Riggs, an assistant professor at the University of San Francisco School of Management and a planner who consults on the future of transportation, says autonomous vehicles, and lower speeds, could allow cities to devote less room to cars by redesigning street infrastructure. “It’s speed and uncertainty that requires such wide roads for human-operated cars,” says Riggs. AV-optimized streets would require fewer signals and intersections—and fewer conflict points between different travel modes. “If city traffic travels slow enough, you could imagine a yielding pocket for vehicles to engage with smoother and operating on much less roadway. A gracious road for pedestrians and cyclists is promising as a feature for autonomous vehicles.”

In other words, it’s like that old Navy Seal adage: Slow is smooth, smooth is fast. That’s also the idea behind “green wave” signal timing, which is now getting a pilot in New York City. Traffic flowing at 15 mph allows for fewer red lights.

The most stubborn barrier to slowing down the city may be the psychological one: It involves changing user expectations for how roads are supposed to operate. Some states have what are called level of service standards, which require roads to carry a certain number of vehicles per hour, or they place restrictions on cities from lowering speed limits. Riggs says that means city leaders need to expend political capital to fight for those changes. “If you talk at any public meeting about slowing streets, you have citizens who are going to be asking if they going to be delayed. There’s going to be friction as we apportion our street in a way that facilitates the future of traveling.”

That friction has been something Riggs has run into firsthand on the streets of Palo Alto, where Waymo’s autonomous vehicles have been testing. “I was behind an autonomous car on my drive back from the hardware store, and I was so frustrated. Why? Because it was obeying the law. I wanted to go 40 mph, but it was a 30 mph street.”

When he finally passed the AI-driven car, Riggs raised his hand to make a familiar gesture of human impatience. But it was a futile one.

“There was no one paying attention in that seat,” he says. “There is a tendency to want to travel faster than we should, and in unsafe ways. Hopefully, we’re going to be able to engineer out that risky behavior.”

Andrew Small is a freelance writer in Washington, D.C., and author of the CityLab Daily newsletter.

NEXT STORY: City Will Try Keeping Public Toilets Open Overnight to Help Curb Poop Problems