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Intelligent Machines

A Single Autonomous Car Has a Huge Impact on Alleviating Traffic

Even intelligent cruise control systems could be used to clear up congestion.

In this replication of a phantom traffic jam, just a single car with limited autonomy (the silver SUV) is enough to clear up congestion involving 20 other cars.

It’s sometimes argued that the long-term benefits of self-driving cars, such as safer roads, may not be felt with much impact until robotic vehicles account for the majority of traffic on the road. Until that happens, those unpredictable lumps of meat we call humans will continue to exert their own effects on traffic—continuing to cause accidents, for instance. But a new study out of the University of Illinois at Urbana-Champaign suggests that the addition of just a small number of autonomous cars can ease the congestion on our roads.

You’ve likely seen the demonstration of phantom traffic jams where cars drive around in a circle to simulate the impact of a single slowing car on a road full of traffic. One car pumps its brakes for no particular reason, and the slowdown ripples through the traffic. Now, the University of Illinois research, led by Daniel Work, shows that placing even just a single autonomous car into one of those circular traffic simulations can dampen the effects of the phantom traffic jam.

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The team’s results show that by having an autonomous vehicle control its speed intelligently when a phantom jam starts to propagate, it’s possible to reduce the amount of braking performed further back down the line. The numbers are impressive: the presence of just one autonomous car reduces the standard deviation in speed of all the cars in the jam by around 50 percent, and the number of sharp hits to the brakes is cut from around nine per vehicle for every kilometer traveled to at most 2.5—and sometimes practically zero.

Because fuel use increases when when cars slow down and have to get back up to speed, the presence of the autonomous vehicle also reduces fuel consumption. According to the calculations by the team, in fact, the savings is as much as 40 percent when averaged across all the cars in the traffic flow.

It’s interesting that these improvements can occur even with a single vehicle in a flow of 20 other cars. And it’s also worth noting that the level of autonomy required to have this effect isn’t the kind that Waymo, Uber, and others are seeking to build—it’s more akin to the adaptive cruise control already featured in many higher-end cars. So while we might have to wait a little longer for all of autonomy’s effects to be felt, its ability to reduce traffic congestion could be here rather sooner than we anticipated.

(Read more: arXiv, “Technology-Induced Distracted Driving Is Pushing Up Insurance Prices,” “Self-Driving and Electric Cars Are Going to Have Tons of Strange Effects on Society”)

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