Most people know that it’s possible to save tons of gas and money by driving more efficiently, and most people completely ignore this and just tear-ass around at whatever speed won’t get them maximally arrested. But EcoSpeed, an app forthcoming on iPhone, Android, and so forth, translates energy-saving theory into action you can take in the real world. And it can save you up to 30 percent on fill-ups.

The app creates routes which privilege the best fuel mileage (as opposed to something like Google Maps, which will only give you the shortest or quickest routes). Then it monitors your driving while you’re on the road, in order to provide you with the optimal speed to drive and other energy-saving feedback.

EcoSpeed is meant to balance sometimes-competing desires like spending less money on fuel, helping the environment, and getting to a destination on time. The company’s demo offers route options ranging from “faster speed” to “greater savings.” The “EcoSpeed” option is the middle option — the porridge that tastes juuuust right.

I played around with the demo briefly, and none of the routes I tried changed at all depending on whether I chose speed, savings, or EcoSpeed. The real-time feedback could be useful, though. It’s not clear if the driver’s meant to be looking at her phone to see the optimal speed or at the road or if there’s another communication mechanism. Our advice: Do not buy this app if you are the type of person who gets annoyed at the GPS and starts yelling at it. But maybe do buy it if you’re more likely to yell at the gas pump numbers for going up too high.

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