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When Will AVs Actually Start to Smooth Traffic Flows?

A study by Carnegie Mellon University found that if at least 20 percent of cars are autonomous vehicles, traffic systems may start to see the operational improvements these vehicles are expected to bring.

Digital illustration of connected autonomous vehicles navigating an intersection as seen from above.
Autonomous vehicles have the ability to make traffic move smoother. But first, they need to be more widely deployed. And that means creating the right regulations for the right cars.

At least 20 percent of the vehicles on the roadways will need to be autonomous in order to realize the traffic operational gains that come with connected vehicles, according to new research from Carnegie Mellon University.

“One of the goals of our work was to quantify the amount of AVs [autonomous vehicles] under which we would begin to realize these traffic and congestion benefits; surprisingly, we found that only 20 percent are needed,” said Carlee Joe-Wong, one of the authors of the report, Mixed-Autonomy Era of Transportation: Resilience and Autonomous Fleet Management. “And that 50-ish percent AVs was sufficient for realizing most of the gains.”

The gains Joe-Wong speaks of include the smoother, more choreographed flow of traffic that comes from having the vehicles talking to each other, making collaborative decisions around speed, routing and other factors. AVs have the ability to form a sort of transportation network altogether unlike the solo “selfish behavior” of human drivers, according to the report.

“We envision AVs as being ‘collaborative’ in the sense of having the ability to communicate with each other and make joint decisions,” Joe-Wong explained.

It’s unknown how far into the future you have to look to see streets humming with the smooth, coordinated flow of self-driving cars. Industry observers continue to push that vision further and further out. Today, fully autonomous cars are often conflated with those that include automated driving systems (ADS) — common on a number of cars and requiring a human sitting behind the wheel.

Perhaps clouding just when that future vision — where at least 20 percent of traffic is made up of AVs — comes into focus is today’s regulatory landscape, which has not caught up to the technology, said Allante Whitmore, director of the AV initiative at SAFE.

“What’s missing is, I think, right now, is the consideration of this new technology,” said Whitmore, explaining that regulatory agencies, from the earliest days of auto regulation, have been structured around human-operated cars.

“We have to really think about creating a new approach, because we have a new technology that is disrupting the way transportation’s been thought of up until now,” said Whitmore, speaking on a recent panel discussion hosted by the Urban Institute on Sept. 22. The forum was discussing recent research by the institute into the many issues surrounding autonomous vehicles.

“Maybe we should just introduce a self-driving vehicle as kind of its own,” continued Anil Lewis, executive director of Blindness Initiatives for the National Federation for the Blind. “Because that’s also the problem within the regulatory process as well, because we’re in the process of trying to adapt existing regulations.”

Organizations like the National Association of City Transportation Officials (NACTO) have urged federal regulators like the National Highway Traffic Safety Administration (NHTSA) to develop regulatory rules specific to automated driving systems (ADS), arguing they need their own regulatory environment.

“Forcing ADS into the existing regulatory scheme is inappropriate,” wrote Corinne Kisner, executive director of NACTO, in a Sept. 21, 2022, letter to NHTSA, which has also been charged with developing regulations for fully autonomous systems.

Clearly, transportation systems, the cars themselves and the regulatory environment guiding them, will have to be developed simultaneously because it’s not conceivable that one technology will suddenly replace another. Fully autonomous cars will share the road with vehicles equipped with advanced driver assistance systems (ADAS) and older model cars operated entirely by a human.

“We’re not that far off from some AVs being on roadways,” said Joe-Wong, pointing to the emergence of AV taxi services being deployed in some select cities. “But we’re quite a ways off from having roads solely dedicated to AVs.”
Skip Descant writes about smart cities, the Internet of Things, transportation and other areas. He spent more than 12 years reporting for daily newspapers in Mississippi, Arkansas, Louisiana and California. He lives in downtown Yreka, Calif.