The fuel efficiency in autonomous vehicles could improve by up to 10 percent if vehicle testing is updated for self-driving capabilities, according to a recent study.

Researchers at the College of Engineering at Carnegie Mellon University determined that the bump in fuel economy would result from changes to the Environmental Protection Agency's fuel economy and emissions standard tests. These updates would take into account any early autonomous vehicle designs that are likely to appear as automotive companies develop self-driving technology.

The study also warns that vehicle efficiency could degrade if autonomous technology is not considered in EPA testing. Researchers suggest that fuel economy could fall by up to 3 percent, depending on the programming of the autonomous vehicle.

"Because existing standardized tests don't consider AV technologies, there are limited incentives for car manufacturers to design cars for optimum fuel efficiency," said Constantine Samaras, assistant professor of civil and environmental engineering at Carnegie Mellon University. "The EPA can use our research as a starting point in redesigning fuel economy testing for autonomous vehicles."

The study was conducted by Samaras as well as Avi Chaim Mersky, a Ph.D. student. The researchers say the EPA tests currently do not take semi-autonomous technologies, such as adaptive cruise control, into account. They sought to determine how fuel efficiency would be impacted by including these features in the testing, as well as future technologies as autonomous developments shift more functions from the driver to the vehicle itself.

Samaras and Mersky say connected autonomous cars could have a particularly strong effect on fuel economy in self-driving cars. Connected vehicle technology allows vehicles to better predict traffic behavior, potentially leading to smoother acceleration and deceleration and more efficient fuel use.

The study simulated a variety of tests that included autonomous technologies, including how self-driving cars will perform when sharing the road with conventional vehicles and how connected vehicle technology can affect fuel economy by conveying information to other vehicles. Researchers found that connected vehicle technology allowed vehicles more time to plan their actions, and that this resulted in an increase in fuel efficiency.

"What we have quantified is that fuel economy testing will need to account for AV technologies in the not-so-distant future," said Mersky.

Other organizations have also suggested that autonomous vehicles will improve fuel economy for a variety of reasons. A 2014 report by the Intelligent Transportation Society of America predicted that autonomous technologies can cut fuel use and greenhouse gas emissions by 2 to 4 percent each year for the next decade as these features become more common.

Julia Pyper, writing for Scientific American, says several developments could result in this benefit. These would include additional connected car technologies, such as traffic signal synchronization and systems to reduce the time a driver spends looking for a parking spot; adaptive cruise control and other features to create free-flowing traffic conditions and alleviate congestion; and the ability of vehicles to travel closer together, thereby improving aerodynamics.

There have been some suggestions that autonomous vehicles could increase fuel use and emissions by altering road use. Will Troppe, writing the Rocky Mountain Institute—a nonprofit organization dedicated to the sustainable use of resources—says self-driving vehicles may encourage people to live farther away from their workplace or make additional trips. He says the ability to read, sleep, or otherwise avoid active driving during travel might also cause people to favor autonomous vehicles to public transportation.

However, Troppe says other factors could favor the opposite trend. In addition to the improved efficiency of vehicle operation, autonomous vehicles could accommodate more lightweight and fuel-efficient vehicle designs. Troppe says autonomous vehicles could also support expanded car sharing programs, allowing multiple people to use the same vehicle for everyday trips.