Wadud said that cars can save a lot of energy and fuel without becoming fully automated. The important thing is that they are able to talk to each other. This will help them drive closer together without bumping into each other, and thereby take advantage of the aerodynamic drag effect.
"The majority of energy efficiency benefits can take place at lower levels of automation," he said. "You do not need self-driving cars."
The study also found that people who usually don't drive as much -- such as the elderly or those with disabilities -- might start driving more with automated vehicles. That could push down energy savings by as much as 10 percent.
The electronic demands of these new cars -- with more touch screens and TV monitors, might require up to 11 percent more energy to run as well.
Jeff Gonder, a transportation systems analyst at the National Renewable Energy Laboratory in Golden, Colo., said the energy benefits of driverless cars are still a big question.
"People are going to do what is most convenient for them, Gonder said. "If there are more cars on the road, but the train is faster, they will take the train. If they have trouble getting to the train and it adds a lot to their journey time, and can have an inexpensive automated vehicle chauffeur them door to door. They might do that."