The U.S. Environmental Protection Agency and Chrysler have teamed up to make hybrid minivans that could be cheaper than current hybrid systems, which get energy in part from braking to charge the battery. What the EPA and Chrysler are working on is a way to capture energy with a hydraulic system - this system can get more energy from braking than conventional systems. From MIT's Technology Review: "To make the system work in minivans, engineers will need to find ways to incorporate bulky air storage tanks--which take up more space than the car's gas tank--without eating into cargo or passenger space, and without compromising safety." There already are some big vehicles with this kind of hybrid system, like garbage trucks. They can "save more than 1,000 gallons of fuel per year on average, reduce emissions by up to 20 percent, and, by reducing the use of friction brakes, extend brake life by up to 300 percent."

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