The benefits that hybrid versions of cars, light-duty pickups, and SUVs bring to the environment–as well as to the driver's wallet, given today's fuel costs–soon will extend to medium-duty fleet operators. Several truck manufacturers are developing hybrid work trucks, with a few aiming to release theirs to the North American market in the next year.

International Truck and Engine is among the many manufacturers that are developing diesel-engine hybrid trucks for medium-duty applications. Such trucks feature greater fuel efficiency and lower emissions than traditional diesels. Peterbilt, International Truck, Kenworth, Mack Trucks, Volvo, Mitsubishi Fuso, and Freightliner are in various stages of developing diesel-electric hybrid trucks for medium-duty applications. Some are developing models for utility and delivery applications, while others are initially focusing on refuse collection. Most manufacturers expect to develop hybrids for additional applications, including materials distribution and delivery.

Medium-duty hybrids offer greater fuel efficiency and lower emissions than standard systems with equal or better performance, manufacturers report. Hybrid systems are most valuable to those operating in urban environments because they use "regenerative braking." During braking, a hybrid's electric motor is used to slow the truck by operating in reverse, generating energy that is then stored in the batteries for later use, such as at the next move away from a stop. "In stop-and-go situations, there will be substantial fuel savings, and the emissions reductions are good," says Dan Cutler, executive director of product development for Isuzu Commercial Truck of America (circle 108). (Isuzu sells hybrid trucks in Japan and is considering bringing models to the Americas.) Regenerative braking also reduces wear and tear on brake components.

A January 2006 study by the American Council for an Energy-Efficient Economy reported that Class 3 through 8 short-haul trucks could realize a 50% gain in fuel economy from hybridization. Such hybrid vehicles, the study concluded, would recover incremental purchase costs through fuel savings over the life of the vehicle. Prices for a medium-duty hybrid are expected to be higher than a standard equivalent, but as there are no models on the market yet, manufacturers are unwilling to say just how much they'll cost. The same study also found that Class 2b trucks (those falling between 8,500 and 10,000 GVWR) also can benefit from hybrid systems in the form of fuel-economy improvements of 50% to 66%. Manufacturers indicate their hybrids may qualify the purchaser for a tax credit under the Energy Policy Act of 2005.

Tony Greszler, vice president of advanced engineering for Volvo Power Train, warns, however, that fuel economy will always depend on a truck's duty cycle. Until manufacturers increase production volumes, the upfront cost of a hybrid may be prohibitive for many businesses, so alternative fuels will likely remain a more affordable, though not universally accessible, way for dealers to reduce emissions and fuel costs for the next few years.

There are several alternative fuels in production and available for use in medium-duty diesel trucks, including biodiesel blends made from various renewable sources, liquefied petroleum gas (LPG or propane), and compressed natural gas (CNG). Using low-level biodiesel blends such as B2 (2% biodiesel, 98% diesel) or B5 (5% biodiesel) does not require engine modifications, but using B100 (100% biodiesel) may. LPG and CNG do require engine modifications.

Alternative fuels produce fewer greenhouse gas emissions and particulates, but most do not deliver the same energy levels that gasoline or diesel provide, making them slightly less efficient. However, the Energy Information Administration (EIA), the statistical agency of the Department of Energy, says that in low-level blends such as B2 or B5 biodiesel, the impact on truck performance and efficiency is barely noticeable. Guy Rini, director of advanced propulsion systems for Mack Trucks, agrees that although standard diesel is the most efficient fuel available, any decrease in efficiency and performance from a switch to an alternative fuel is minimal. For example, biodiesel's energy content is 10% less than standard diesel No. 2, which equates to using 1.1 gallons of biodiesel to get the same power provided by one gallon of standard diesel.

The cost of biodiesel is comparable to No. 2 diesel, although this depends on the blend, its source, and on local market conditions.

It's important to note that though hybrids will offer the greatest efficiencies, emissions advantages, and performance advantages compared to other vehicles, even those using alternative fuels, hybrid and alternative fuel technologies are not mutually exclusive, says Doyle Sumrall, director of strategic operations for the National Truck Equipment Association. "You could have an alternative-fuel hybrid vehicle. There's an awful lot of technology that we're really just learning how to control and integrate with various elements, and integrate into various work applications," he says.

–Stephani L. Miller