The term “hybrid vehicle” typically brings to mind small, oddly shaped passenger cars like Toyota's Prius, not a beefy 64,000-lb. truck. Yet that's what the Mack Trucks division of Sweden's Volvo Group is delivering to the U.S. Air Force: a prototype Granite dump truck that sports an electric motor paired with a 365-hp. diesel engine. It's equipped with what the OEM calls “ultra-capacitors” instead of massive batteries to boost fuel economy anywhere from 30% to 35%. By burning less fuel, there are emissions benefits as well.

It's the latest in a line of six heavy-duty hybrid truck models Volvo and Mack have built for the Air Force as part of a $6.8-million contract. Though hybrid vehicles of this size and scope are very expensive compared to their strictly diesel-powered brethren, both Volvo and Mack see great future potential in the commercial market if government incentives can spur enough initial purchases.

“There are a lot of customer benefits to heavy-duty hybrids,” Paul Vikner, president and CEO of Mack trucks explained at a special event in Washington D.C. at the Swedish embassy in Washington, DC, last month. “It starts with … fuel savings of 30% to 35%. Then by burning less fuel, you are reducing emissions. You're also looking at having an auxiliary power source that, for refuse and other vocational operations, may eliminate the need for a PTO [power take off],” he said.

However, Vikner is well aware of the cost concerns customers have about hybrids. “The initial cost of the technology is the biggest” he said. “There's also the long-term reliability of hybrids; these are concerns we're working on now.”

The Mack hybrid truck is slated for full field tests in 2008, with full production scheduled for 2009.

According to Volvo Group CEO Leif Johansson, “The cost calculation for these vehicles is also very application-dependent. The more stops and starts a vehicle has, the more savings a hybrid generates. We think a hybrid in such an application — such as a refuse vehicle — could have a one- to three-year payback. That is what would make this technology commercially viable.”

“In a refuse vehicle application, we're using electricity just to launch the vehicle, to get it up to 4.5 mph, at which point the diesel engine comes on,” said Guy Rini, Mack's director of advanced propulsion system. “You're getting the truck up to a speed where it's much more efficient to then activate the diesel engine. Look at the fuel efficiency we're talking about here. In an industry where a 3% fuel savings is a big deal; we're looking at over 30% and more in many cases. That's a huge cost savings.”