Even a small number of autonomous vehicles can ease congestion
Researchers at the University of Illinois at Urbana-Champaign have found that the addition of a small number of autonomous vehicles to the roads has a significant effect on easing congestion. Examining phantom jams, in which a single slowing car can cause a slowdown throughout the traffic, Daniel Work and his team found it was possible to reduce the amount of braking performed in a cue of traffic by using a single autonomous vehicle that controlled its speed intelligently. The other vehicles involved also saved as much as 40% in fuel consumption. 
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”)