It has happened to all of us. We are driving on the highway when all of a sudden traffic slows to a crawl. We assume there is an accident ahead but often traffic resumes its normal speed for no apparent reason. “What was that all about?” we wonder. A new study headed by Daniel Work, an assistant professor at the University of Illinois at Urbana-Champaign, finds that having just a few autonomous cars on the road could reduce or eliminate such slowdowns. “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,” he says.
The study was funded by the National Science Foundation’s Cyber-Physical Systems program. It utilized the talents of a multi-disciplinary team of researchers with expertise in such diverse fields as traffic flow theory, control theory, robotics, cyber-physical systems, and transportation engineering. The study highlighted how important a deeper understanding of the dynamic between these autonomous vehicles and the human drivers on the road will be in designing future traffic control systems.
The research was conducted on a test track in Tucson, Arizona. A single autonomous vehicle circled the track continuously with at least 20 other cars operated by human drivers. Under normal circumstances, human drivers naturally create stop-and-go traffic even in the absence of bottlenecks, lane changes, merges or other disruptions. This phenomenon is known as the “phantom traffic jam.”
The researchers found that by controlling the pace of the autonomous car, they were able to smooth out the traffic flow for all the cars. The study showed that even a small percentage of autonomous vehicles can eliminate those waves and reduce the total fuel consumption by up to 40 percent. “Before we carried out these experiments, I did not know how straightforward it could be to positively affect the flow of traffic,” Sprinkle said Jonathan Sprinkle, an associate professor of electrical and computer engineering at the University of Arizona. “I assumed we would need sophisticated control techniques, but what we showed was that controllers which are staples of undergraduate control theory will do the trick.”
This study suggests that adaptive cruise control systems can improve the flow of traffic even before there are large numbers of autonomous vehicles on the road. “Fully autonomous vehicles in common traffic may be still far away in the future due to many technological, market and policy constraints,” says Benedetto Piccoli, a professor of mathematics at Rutgers. “However, increased communication among vehicles and increased levels of autonomy in human-driven vehicles is in the near future.”
Programming cars for autonomous operation is more challenging when there are only a few of them on the road than it will be in the future when vehicle to vehicle connectivity is more common. “The proper design of autonomous vehicles requires a profound understanding of the reaction of humans to them,” says Benjamin Seibold, associate professor of mathematics at Temple University. “Traffic experiments play a crucial role in understanding this interplay of human and robotic agents,” he says.
The researchers say the next step will be to study the impact of autonomous vehicles in denser traffic with more freedom granted to the human drivers, such as the ability to change lanes.
Source: Electric Vehicles Research Photo credit: University of Illinois