Urban Planning and Design

Smart intersections won’t help cities without smart policy

The first thing that should pop into mind with the future of mobility is people, not cars.

By Eric Jaffe

Illustration of city intersection

Light Traffic | MIT Senseable City Lab

There's a lot you won't see in this fun video of an autonomous vehicle "smart intersection" from MIT's Senseable City Lab making news rounds. You won't see long lines of cars forming at traffic lights. You won't see traffic lights at all. The slot-based intersection uses sensor data from oncoming vehicles to coordinate their safe-but-nonstop movements. You won't see congestion delay, because it no longer exists.

What you also won't see are pedestrians. This omission occurs despite the fact that the smart intersection was derived from Massachusetts and Columbus avenues in Boston, a crossing typically filled with plenty of people in the city's South End. The official video description insists the intersection "is flexible and can be designed to accommodate pedestrian and bicycle crossing with vehicular traffic." But just how that's the case is one more thing that's hard to see.

That's not to jab at the fine folks at Senseable City. As I've pointed out, other smart intersection models have also left out people. These exercises come with the best of intentions: help reduce the congestion that makes daily travel so frustrating for metro area residents. But their mistake is suggesting that technology alone can solve urban problems. On the contrary, smart intersections without smart, people-first policies will only make things worse.

City history offers a perfect parallel. Long before the dream of autonomous intersections, Chicago implemented a technology back in 1926 that also promised to end traffic: signal optimization. This engineering innovation, as well as its unintended social impact, is chronicled by Peter Norton of the University of Virginia's Center for Transportation Studies in his masterful 2011 book, Fighting Traffic.

Before that time, traffic lights along a corridor all changed at once, sometimes at the manual control of a police officer. This approach brought great order to roads but also created lots of congestion. So an emerging crowd of traffic engineers took charge of the problem, studying traffic volumes on each block and timing the signals for optimal flow --- with "optimal" defined as whatever created the least amount of vehicular delay.

Chicago brought this engineering marvel to life on February 7, 1926. Traffic lights at 49 intersections were connected to timers and wired to "a central electromechanical brain in the basement of City Hall," writes Norton. The result was a huge improvement in car flow. Drivers could travel a full four (!) straight intersections without stopping. News reporters described the system from a driver's perspective as "an instant and unqualified success."

But the people who had once been able to cross these city streets freely saw things differently. Here's Norton (my emphasis):

To most traffic engineers, well-timed signals maximized a street's vehicular capacity. Pedestrians were left out of their equations. Many city people faulted coordinated signals for making it more difficult than ever to cross streets. Cars sped along faster, giving pedestrians fewer safe opportunities to cross at mid block or at red lights. In the Chicago system's first week, the Tribune reported that "the walker found life one succession of heart thrills, dodges, and jumps." ... Because signal timings in coordinated systems were based on vehicle speeds, they helped to redefine streets as motor thoroughfares where pedestrians did not belong.

The point is not that the technology of timed lights ruined cities. Technology on its own has no such power. Rather, the point is that the "smart intersections" of 1926 were paired with misguided public policies that gave cars dominion over city streets. The consequences of this car-first framework still linger today: curb designs and lane widths that facilitate high speeds, metrics that evaluate street success on reduced auto delay, even traffic itself.

If technologists and urbanists start preparing together for a driverless future with these lessons in mind, then tomorrow's city streets might be smart after all. You can imagine a regulatory framework that prices roads to reduce excessive use and congestion, and that incentivizes vehicle sharing and clean energy to reduce pollution. And you can imagine policy that pushes fast traffic to the fringes, freeing the urban core for pedestrians.

But you can't imagine any of that unless the first thing that pops into mind is the people.