Four principles for the future of city streets
This piece was co-written with Graduate Associate Landry Doyle-Wiese.
In the 1920s, American cities debated a question that would shape urban life for decades: “Who is the street for?”
Streets had, for ages, existed not just as thoroughfares but as vibrant hubs of commercial and social activity. And so, at first, the answer was almost everyone: adults, children, horses, buggies, streetcars, vendors, and more.
But the automobile changed that concept. At first, the new technology was seen as a dangerous invader of places where children played, streetcars crossed, and pedestrians strolled — with good reason. In 1925, cars killed over 15,000 people a year. But by the end of the decade, thanks in part to the careful machinations of the car lobby (which went so far as to coin and promote the word “jaywalker” to liken wayward pedestrians as uncouth bumpkins, or “jays”), streets became conduits that get people where they need to go — in fast vehicles.
As Peter Norton explains in his book, Fighting Traffic: The Dawn of the Motor Age in American Cities, cities were “physically destroyed and rebuilt to accommodate automobiles.” Curbs, crosswalks, and traffic lights were installed for the first time to ensure that pedestrians remained in their small portion of the street’s real estate — and crossed only when it was most efficient for vehicles.
These kinds of measures have only escalated over time. To handle peak, rush-hour demand, engineers today will often add more vehicle lanes to cities. And to ensure the safety of pedestrians and cyclists on these high-speed streets, they design even wider vehicle lanes (to account for drivers who drift or veer) and include buffer spaces like shoulders, medians, and parked cars. These acres of pavement — empty for most of each day and night — are neither pleasant to walk around nor conducive to the types of welcoming urban spaces that encourage street life.
Worse, despite all these efforts, our streets are neither efficient nor safe. In 2018, due to congestion, nearly every major U.S. city recorded a downtown last-mile travel speed below 20 miles per hour. In 2017, more than 6,700 pedestrians and cyclists died on U.S. streets due to automobile crashes.
In response to this stark reality, the complete streets movement has pushed forward important design solutions for cities to improve safety and sidewalk activity — while still making sure people can get where they need to go. Cities like Boston and Toronto, for example, have published Complete Streets Guidelines to promote design standards that allow pedestrians, bicycles, and public space to co-exist with cars safely. In 2017, NACTO released its Blueprint for Autonomous Urbanism to “proactively guide the [self-driving car] technology to prioritize people-first design.”
At Sidewalk Labs, we think that there is an opportunity to push this critical thinking even further. We are on the cusp of a new era where new technological capabilities are about to converge. These include autonomous vehicles, which can be programmed to follow speed limits or take certain routes; new mobility services like ride-hail and bike-share services, which reduce the need for parking space; and flexible infrastructure, which makes it possible to use street spaces in a variety of ways. These advances have put cities in a position to completely re-imagine streets — and who they are for.
With these trends and capabilities in mind, we’ve developed four principles that have guided the ways we approach street design — and that we think could guide the design of streets in the future. (You can learn more about them, and download the full report on the principles, here):
- Principle 1: Tailor streets for different modes.
- Principle 2: Separate streets by speed.
- Principle 3: Incorporate flexibility into street space.
- Principle 4: Recapture street space for the public realm, transit, bikes, and pedestrians.
Principles 1 and 2 go hand in hand: different street types could prioritize different modes — and adjust their width and speed limit accordingly. So do Principles 3 and 4: we can use new technologies to make lanes more flexible — and give space back to people whenever possible.
To illustrate these admittedly abstract concepts, let’s examine how they’d play out in practice on different street types.
Let’s start with streets that prioritize pedestrians. We’ve called these streets Laneways — they’re very narrow and limited to 4mph. Pedestrians would feel comfortable to stroll or linger here.
Streets that prioritize cyclists — Accessways — are slightly wider and have a speed limit of 14 mph; here, cyclists can travel naturally, without being hemmed into “safe zones,” since the majority of space on that street type is dedicated to cyclists’ use.
Another street type — called Transitways — are wider still. They allow for all modes except cars and always give priority to public transit through dedicated lanes and signal priority.
Finally, we’ve called streets that allow for all modes, including cars, Boulevards. Consistent with “complete streets” principles, they include barriers and have a speed limit of 25 mph.
Although cars would only be allowed on Boulevards, emergency, disabled access, and connected autonomous vehicles would be allowed on all street types (more on that last point below).
These four street types, with their corresponding designs and speed limit interventions, would already go a long way to improving the safety and vibrancy of the public realm. But with new technologies, even more could be achieved.
Raised concrete curbs could be removed in favor of curbless, LED-embedded pavement that can — with the flick of a switch — signal a change in the number of lanes, the width of the “sidewalk,” or even the direction of the street. At rush hour, street space on a Boulevard could be reserved for high person-throughput modes, such as transit. At off-peak hours, or perhaps on a designated holiday, it could be easily converted into public space. With these dynamic curbs, Boulevards could be narrower overall and still serve multiple uses, based on demand.
Managing this new curbside demand would require a system that understands congestion patterns in real-time. Low-cost sensors and machine-learning simulation models can together inform a mobility management system that adapts to new and predicted conditions by reallocating lanes, changing speed limits or pricing, or adjusting signal timings to keep all modes moving — and safe.
Much like Barcelona’s superblocks, we imagine that higher-speed Boulevards would form a perimeter around a network of lower-speed Accessways and Laneways. But to truly ensure speed and efficiently for all users, connected and autonomous vehicles (CAVs) would be critical. CAVs — including e-bikes and e-scooters — can be programmed to follow speed limits, to stay out of areas that are restricted, to interact safely with cyclists and pedestrians, and to operate in narrow streets. What’s more, speed limits and navigation technology should lead CAVs to naturally select the faster, wider streets for the most efficient trip. And pedestrians and cyclists would similarly select the streets designed for them, where they could comfortably get where they needed to go without worrying about interacting with dangerous modes.
In the coming year, we’ll test our principles — and the street designs they inform — by installing prototypes and gathering feedback from experts and communities. The goal of these prototypes will be to gauge how drivers, pedestrians, and cyclists react to these designs and, in particular, the dynamic elements.
Our hope is that, as cities enter the 2020s, that old question of whom streets are for will be resolved. The street will once again be a place to stroll, play, and get around safely — for everyone.
If you’re a mobility engineer, planner, advocate, provider, disrupter, or enthusiast, we want to hear from you. Help us drive towards the next version of these designs by sending your feedback to firstname.lastname@example.org.
April 26, 2019