UPS announced that it has placed an order for seven hydraulic hybrid delivery vehicles to be introduced between 2009 and 2010, Autopia reports, in what will prove to be a high-profile test of a little-known, EPA-developed technology that mates a diesel engine with an innovative hydraulic propulsion system.

"In most hydraulic hybrids, according to Design News, the diesel engine powers a pump that charges an accumulator, which drives pump motors connected to the wheels," the article said. "Without a conventional drivetrain and transmission, the engine can run at maximum efficiency at all times. During braking, the pump motors are reversed and can recapture at least 70 percent of braking energy—nearly three times the amount that can be recaptured in the regenerative braking systems found in electric hybrids."

That means a 50 percent increase in fuel economy compared to regular UPS trucks, along with a 30 percent decrease in harmful emissions. UPS plans to test the seven vehicles in Minnesota over the next 18 months. "There is no question that hydraulic hybrids, although little known to the public, are ready for prime time use on the streets of America," UPS chief operating officer David Abney said in a company statement.