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Center for Transportation Studies

Programs & Labs

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Summer 2011

Seminar: Can fuel-economy displays promote safe, fuel-efficient driving?

The power to increase fuel efficiency isn’t up to auto manufacturers alone. Efficient driver behavior can also help achieve large reductions in fuel consumption. In a recent study funded by the National Highway Traffic Safety Administration, ITS Institute researchers investigated fuel-economy display (FED) devices that provide feedback on driver behavior to determine their contribution to fuel savings.

At a recent research seminar, Justin Graving, a research fellow at the ITS Institute’s HumanFIRST program, presented his work evaluating how features of fuel-economy displays affected fuel consumption during simulated driving. Study results indicated that the presence of a fuel-economy display promoted fuel-efficient driving, but also showed that when instructed, drivers were able to reduce their fuel consumption without the aid of a display.

The U.S. Department of Energy suggests that driving sensibly (no hard braking, reducing aggressive driving, and reducing rapid acceleration) can improve a car’s fuel efficiency by 33 percent, and observing the speed limit can improve it by 23 percent. Other behaviors that can help improve fuel efficiency include not idling for longer than 20 seconds at a time, using cruise control and overdrive gears, avoiding changes in momentum, and keeping the windows up at speeds of 40 mph or higher.

If such drastic results can be achieved through driver behavior alone, the obvious question is: How do we get people to drive more efficiently? The answer, Graving said, is either through training or by providing feedback to drivers through fuel-economy displays.

Graving’s project set out to accomplish two primary goals. The first, to document the design range of FEDs, aimed to determine the similarities and differences across the many different devices in the marketplace, where there are no existing guidelines for design. Building on this work, the second goal was to identify common display components that helped drivers improve their efficiency and present recommendations to auto manufacturers for inclusion within larger stylistic changes.

“There’s a wide range of potential designs out there and a lot of times the manufacturers just follow what they think the consumers want...but there’s no clean, clear evidence that those displays actually help,” said Michael Manser, director of the HumanFIRST program and member of the project team.

The project team selected three key components to include in the test FEDs: combined short-term (e.g., instant mpg meters) and long-term (e.g., trip average mpg meters) measures, one or more unique measures (e.g., ambient meters that change color based on rates of fuel consumption, and meters to show how acceleration affects fuel consumption), and an indicator of driving impacts on fuel consumption. Incorporating these components into six unique displays, the researchers presented images of them to 13 human subjects and asked them to rank how easy it was to comprehend the information in each of the displays.

Based on their feedback, the researchers created two FEDs—one showing how acceleration affected fuel efficiency (too low or too high), and one showing instant fuel economy. Both displays also included a trip average indicator. Graving and his team then evaluated the impact these displays had on fuel economy within the context of simulated driving. Thirty human test subjects were asked to drive fuel efficiently in the HumanFIRST driving simulator and were assigned the acceleration display, the instant fuel economy display, or no display at all. None of the subjects were given instructions on how to drive fuel-efficiently.

The study results showed that both the FED group and the control group members (who were only asked to drive more efficiently) were able to increase their mpg significantly (11 percent and 4 percent, respectively). Graving concluded that in an environment with little or no traffic, a fuel-economy display could be an effective tool for increasing miles per gallon. “Within an urban environment when traffic is present you may have a benefit in mpg with a fuel-economy meter, but the features of the display could prove distracting, depending on the design,” Graving said. Further research is needed to support a conclusion that having a fuel economy display in a vehicle compromises driving safety by contributing to distraction, because its presence may not be problematic. It’s important to develop and test other ways to deliver fuel economy information, such as with auditory messages, that do not lead to looking away from the road frequently, Graving said.