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Bye-bye traffic lights

When self-driving cars rule the roads, lots of things will be different: You won’t have to worry about finding a parking spot, it will be hard to earn a speeding ticket, and, according to some forward-looking thinkers, there will no longer be a need for traffic lights.

The proposal to relegate red lights comes from MIT’s Senseable City Lab and is described in a paper published in March in PLOS ONE. Instead of drivers lining up behind traffic lights and waiting their turns, the MIT team envisions what they call “slot-based” intersections, where self-driving cars regulate their speed to arrive at a crossing just at just the right time, threading the needle of oncoming traffic.


“When sensor-laden vehicles approach an intersection, they can communicate their presence and remain at a safe distance from each other, rather than grinding to a halt at traffic lights,” explains Carlo Ratti, director of the Senseable City Lab, in an email. “By removing the waits caused by traffic lights, slot-based intersections create a system that is much more efficient.”

Along with the article describing their proposal, Ratti and his colleagues produced a video simulation of slot-based intersections. In place of a dreary four-way stop, it shows cars shooting through an intersection like high-speed photons, with a precision that would be impossible to achieve with human beings behind the wheel. Compared to the tedium of waiting for the light to turn green, it’s a marvel.

To achieve such futuristic efficiency, Ratti says, cities will need just a few technological ingredients: self-driving cars, of course, which seem to be well on their way, plus a good internet connection to synch data from each car. Thomas Van Woensel, a professor of freight transport and logistics at Eindhoven University of Technology in the Netherlands, thinks there may be other technological hurdles to work out. In particular, he imagines there will need to be some central system that organizes overall traffic flows, like air-traffic control for the roads.


“You’ll need centralized decision-making that organizes flows and intersections. Car-to-car sharing of information is extremely local, while I think global information about the network itself is also extremely important,” he says.

Slot-based intersections may feel impossibly far removed from our current driving reality, but Ratti predicts they’re coming, and soon. He reports that the Senseable City Lab has been working with the Committee on Autonomous Road Transport in Singapore to experiment with the transportation possibilities that emerge with self-driving cars.

Van Woensel also thinks these kinds of transportation changes are on the near horizon. He sees the rise of systems like slot-based intersections as consistent with the way in which transportation infrastructure will continue to migrate from the public space to the private confines of a vehicle. Already, he says, some cities are considering reducing road signage, because it’s unnecessary at a time when everyone’s navigating by GPS. Soon it may be time for traffic lights to make their exit, too, their once formidable signal permanently set to red.

Kevin Hartnett is a writer in South Carolina. He can be reached at kshartnett18@gmail.com.