Package delivery giant UPS (NYSE: UPS), which already is operating 2,022 alternative-fuel vehicles in its fleet, will purchase 130 additional hybrid-electric vehicles (HEV).

The trucks, to be purchased from Freightliner Custom Chassis Corp., will include a hybrid drive system from Eaton Corp.

“Hybrid electric technology has proven itself to be effective in the field,” said Mike Britt, UPS’s director of vehicle engineering. “We are eager to receive these new HEVs in 2011 and get them on the road. Continued investment in fuel-efficient technology is a part of UPS’s overall environmental strategy.”

To be delivered early next year, 100 of the trucks will be deployed in California with the remaining 30 to split between New York and New Jersey. UPS estimates they will save 66,085 gals. of fuel and 671 metric tons of CO2 annually.

UPS’ alternative-fuel fleet includes hybrid-electric, compressed natural gas, liquefied natural gas, propane and all-electric trucks. The company has 250 HEV delivery vehicles operating in the U.S. currently.

The trucks are identical to Big Brown’s iconic delivery trucks, but inside there are big changes. The hybrid-electric power system utilizes a conventional diesel engine combined with a battery pack. The energy generated from braking is captured and returned to the battery as electricity. The combination of clean diesel power and electric power, supplemented by regenerative braking, allows dramatic improvements in fuel savings and emissions reductions, the company said.