The U.S. Environmental Protection Agency (EPA) unveiled this week the first-ever series hydraulic hybrid diesel urban delivery vehicle. The development of the hydraulic hybrid is the result of a partnership between the EPA, U.S. Army, UPS, International Truck and Engine Corporation and Eaton Corporation.The EPA and UPS plan to evaluate the vehicle's fuel economy performance and emissions during a series of tests in 2006. In laboratory testing, the EPA's patented hydraulic hybrid diesel technology achieved a 60 to 70 percent improvement in fuel economy and more than a 40 percent reduction in carbon dioxide emissions, compared to a conventional UPS vehicle.The EPA estimated that when manufactured in high volume, the added costs of the hybrid components could be recouped in less than three years through lower fuel and brake maintenance costs.In the series hydraulic hybrid diesel, a high-efficiency diesel engine is combined with a unique hydraulic propulsion system, replacing the conventional drivetrain and transmission. The vehicle uses hydraulic pumps and hydraulic storage tanks to store energy, similar to what is done with electric motors and batteries in hybrid electric vehicles. Fuel economy is increased in three ways: vehicle braking energy is recovered that normally is wasted; the engine is operated more efficiently; and the engine can be shut off when stopped or decelerating.The diesel hydraulic hybrid truck is potentially eligible to qualify for a tax credit that is up to 40 percent of the incremental cost of the vehicle under a provision of the Energy Policy Act of 2005 for medium- and heavy-duty vehicles.