One perceived benefit of self-driving vehicles is their ability to create better traffic flow, helping to reduce traffic congestion. A recent study suggests that this benefit could be realized early in the development of autonomous vehicles, since stop-and-go traffic waves were eliminated with the incorporation of a small percentage of self-driving vehicles.

Traffic waves, also known as phantom traffic jams, are congested conditions that occur as a result of traffic volume and human behavior rather than construction, accidents, or other incidents affecting road conditions. A driver unexpectedly hitting their brakes causes drivers behind them to slow down, creating a wave-like effect that eventually causes a traffic jam.

A team of researchers recently sought to determine what effect an autonomous vehicle could have on traffic jams when mixed into the traffic flow with human drivers. The study was funded by the National Science Foundation's Cyber-Physical Systems program.

Drivers were asked to drive around a small circular track in Tucson, Ariz. Stop-and-go traffic can naturally form on circular test tracks, since traffic waves that form in this constricted area will eventually impede the ability of drivers to proceed. The experiment included one autonomous vehicle among 20 vehicles driven by humans.

By controlling the pace of the autonomous vehicle, researchers found that they could create a smoother traffic flow for the other vehicles on the track. The study concluded that integrating a small number of autonomous vehicles into the traffic flow would not only be simple to do, but could also eliminate traffic waves and reduce fuel consumption by 40 percent.

"Our experiments show that with as few as 5 percent of vehicles being automated and carefully controlled, we can eliminate stop-and-go waves caused by human driving behavior," said Daniel B. Work, lead researcher on the study and assistant professor at the University of Illinois at Urbana-Champaign.

The researchers noted how some currently available technologies already have the ability to make a positive impact on traffic flow. Adaptive cruise control, which adjusts a vehicle's speed to maintain a safe following distance from the vehicle in front of it, is considered a precursor to fully autonomous driving.

"Fully autonomous vehicles in common traffic may still be far away in the future due to many technological, market, and policy constraints," said Benedetto Piccoli, a researcher from Rutgers University. "However, increased communication among vehicles and increased levels of autonomy in human-driven vehicles is in the near future."

Benjamin Seibold, associate professor of mathematics at Temple University, cautioned that it will be more difficult to integrate self-driving vehicles into traffic flow dominated by humans in the short term. The researchers also intend to study the effect of autonomous vehicles on denser traffic patterns as well as the effect of giving them a wider range of functions, such as the ability to change lanes.

"The proper design of autonomous vehicles requires a profound understanding of the reaction of humans to them, and traffic experiments play a crucial role in understanding this interplay of human and robotic agents," said Seibold.