Will the rise of self-driving vehicles signal the death of the traffic light?

International Technology Transportation
(Courtesy MIT Senseable City Lab)

The dawn of self driving cars promises to be an exciting new era for transport. However, what exactly lies ahead is still up for debate. Researchers at the Massachusetts Institute of Technology (MIT), the Swiss Institute of Technology (ETHZ), and the Italian National Research Council (CNR) have outlined how traffic signals could be rendered obsolete if automated vehicles get their way. The development is known as “slot-based intersections,” and if realized, would significantly reduce queuing, delays, and pollution.

If evidence from any science fiction movie is anything to go by, it’s that humans have very little trust in automated technology. It’s easy to picture: panic as your self-driving car appears to be careering into another, only to miss by a a tiny margin, all perfectly predicted by an automated system of course.

That may be an exaggeration, but Professor Carlo Ratti, Director of the MIT Senseable City Lab and his team have produced a model that shows cars zipping through a four-way intersection both without stopping or slowing down and remaining unscathed.

“Traffic intersections are particularly complex spaces, because you have two flows of traffic competing for the same piece of real estate,” he said in a press release regarding the study, published in detail here. “But a slot-based system moves the focus from the traffic level to the vehicle level. Ultimately, it’s a much more efficient system, because vehicles will get to an intersection exactly when there is a slot available to them.”

Trust in such a system would have to be high. Communication between cars would have to be flawless and safety measures for failure would also have to be in place. That said, if implemented, the system would speed up journey time and also reduce pollution by cutting down on the time spent idle at traffic signals.



Of course, signal-less interchanges already exist, they’re called roundabouts. But the possibility for human error (and hence collisions) still exists in the roundabout, along with the need to give way to others.

“Slot-based intersections are similar to slot-based management systems used for air-traffic control,” say the team. “Upon approaching an intersection, a vehicle automatically contacts a traffic management system to request access. Each self-driving vehicle is then assigned an individualized time or “slot” to enter the intersection.”

Speed limits could also change. If a perfect system can plot every movement, why not travel at the fastest, yet safest, possible speed? This is just one of the questions arising as self-driving cars become more and more likely to enter our lives. Would car lanes also be made thinner? Vehicles won’t be making mistakes so why not cram as many in as we can and maximize efficiency?

In terms of having a central traffic organizing system, getting different car manufacturers to be completely open with each other is another major bridge that would need to be crossed.

And as for the more pressing issue of automated vehicles’ interaction with humans, MIT’s Senseable City Lab responds by saying: “slot-based intersections are flexible and can easily accommodate pedestrian and bicycle crossing with vehicular traffic.”

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