For Hybrid Drivers, Every Trip Is a Race for Fuel Efficiency

Evan Hirsche averages 43 mpg with his Prius, while Katie Sebastian, shown with her son, Cole, averages 41 mpg. The drivers have friendly rivalry over their mpg scores, fueled by the Prius hybrid's real-time mileage readings.
Evan Hirsche averages 43 mpg with his Prius, while Katie Sebastian, shown with her son, Cole, averages 41 mpg. The drivers have friendly rivalry over their mpg scores, fueled by the Prius hybrid's real-time mileage readings. (By Kevin Clark -- The Washington Post)
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By Michael S. Rosenwald
Washington Post Staff Writer
Monday, May 26, 2008

Katie Sebastian accuses her friend Evan Hirsche of getting better mileage than she does because he lives in Bethesda and has flatter everyday trips than she encounters in hilly Takoma Park. She suspects the Hirsche family of taking frequent long drives out of town, which also helps them.

"They claim they haven't been out of town in a while," she said, "but I know they have."

Hirsche retorts: "It is well known that Katie is a lead-footer."

Their friendly rivalry stems from the Prius effect. Both drive a Prius, the Toyota hybrid with an elaborate dashboard monitor that constantly informs drivers how many miles per gallon they are getting and whether the engine is running on battery or gasoline power. That can change driving in startling ways, making drivers conscious of their driving habits, then adjusting them to compete for better mileage. (Sebastian has 41 mpg, Hirsche 43.)

The Prius, and other hybrids with similar displays, has triggered on-the-spot learning that has the potential to change energy-consumption habits. The implications go far beyond the family car, with new devices for the home offering ways to encourage significant change in energy use.

"Once you start making fuel consumption more visible, you have something that comes to the forefront of people's minds instead of lurking in the background," said Sarah Darby, a researcher who studies energy feedback technologies at the University of Oxford's Environmental Change Institute. The monitors "show the consequences of your actions," she says. "This gives you feedback that alters actions, and encourages you to try and improve things."

In the Prius and other hybrids with energy displays, drivers can see what specific actions mean for their mileage. In some ways, it is like children learning to color in between the lines, with the teacher standing over their shoulders. Aggressive acceleration after a stoplight -- that's bad. The monitor will show mpg going down. Suddenly slamming the brakes -- also bad. Coasting to a stop -- good. That tactic lets the engine shut down, saving gas. Hills -- oh, they are real bad.

Tom Igoe, a physical-computing researcher at New York University, said the Prius mpg display is one of the best examples of technology "where green meets information systems."

"For a long time," he said, "we have known that people will change their habits if they are exposed to feedback in real time."

Now companies are introducing products that do for the home what the monitor in the Prius has done for the car. The Kill a Watt plugs into a wall and accepts plug-ins from appliances, showing exactly how much energy is being consumed. Sebastian recently bought one at a store in the District. "We want to know where our electricity is going," she said.

The Wattson, a small console designed by a British company, wirelessly connects to a home's energy meter and displays numbers showing how many watts of electricity the house is using. If the console glows blue, less electricity than normal is being used. If it glows red, it's just the opposite.

Massachusetts company Ambient Devices, a spinoff of MIT's famed Media Lab, is testing, in connection with several large U.S. utilities, a device called the Orb. It is a small frosted-glass ball that changes color based on how much demand is on the electricity grid. You can put it anywhere in the house, like a piece of modern art. When demand is high, consumption costs more, and the Orb turns red. When it's low, the cost falls, and the Orb turns green. Homeowners can adjust their consumption accordingly, perhaps not washing the dishes when the energy grid is being taxed and the Orb is red.

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