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How self-driving cars could make traffic lights obsolete, in one unsettling video

We've only begun to think through how self-driving cars could one day reshape our roads, cities, and lives — for better and for worse.

They might, for example, make traffic lights obsolete. Which... is actually a bit unsettling.

In the video above, researchers at MIT’s Senseable City Lab demonstrate how streets full of autonomous vehicles wouldn't necessarily need stoplights. If the cars were all communicating with each other, they could simply slow down a bit and "slot" their way through intersections at steady speeds without ever causing a collision.

The model for "slot-based intersections" is described in this recent paper in PLOS One. The researchers found that reducing reliance on stoplights would greatly cut down on delays and congestion. No more waiting for the light to turn green. Cars would lower their speed to fit into a "slot" and then breeze right through the intersection without stopping. Sounds wonderfully efficient, right?

Except this also raises some difficult urban-planning questions. Slot-based intersections obviously don't work for places where pedestrians need to cross. Or for bicycles. So what do you do there? More broadly, accommodating people who walk or bike is going to be a major challenge for autonomous vehicles (AEVs). There's a real risk that in an AEV-centric future, roads could end up catering far more to cars than they do today — pushing everyone else out.

Granted, this technology is still a long, long ways off, as Kevin Hartnett nicely points out in the Boston Globe. Cars will first need to be able to communicate not just with each other but likely with a central traffic controller. And roads would have to be filled entirely with autonomous vehicles — if you had even one human driver, that could muck up the flow. A stoplight-free future is decades away, maybe more.

Even so, it's a good example of how radically self-driving cars could remake our transportation systems, in positive and not-so-positive ways. As my colleague David Roberts says, it's wrong to imagine that AEVs will simply replace conventional vehicles on the road in a 1-1 fashion and all else will stay equal. All else won't stay equal. Massive systemic changes are likely to emerge from a future filled with AEVs — changes that are very difficult to predict in advance. It's much like how the advent of the internet didn't simply replace the postal service.

The end of stoplights is one example of a possible systemic change with far-reaching implications. No doubt there will be many more.

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