At a time when hybrid passenger cars and light trucks are becoming hot consumer items, the numbers of hybrid heavy-duty vehicles, such as utility trucks and buses, are lagging behind severely, despite the availability of the technology and its potential to significantly reduce fuel consumption.

Heavy-duty vehicles are an important target for reducing U.S. dependence on foreign oil because, while they make up less than 10 percent of all the vehicles on the roads, they consume about half the fuel. But, says Bill Van Amburg, senior vice president of WestStart, a Pasadena, CA, nonprofit working to increase the adoption of advanced energy technologies in vehicles, the federal government could do much more to help get fuel-saving technology on the roads.

One exception are public transit buses. Federal subsidies for hybrid transit buses makes them a reasonable option for transit agencies, says Tom Bartley, manager of new business at ISE Corporation, Poway, CA, which makes battery and ultracapacitor-based hybrid systems for buses. Already, about 800 hybrid public transit buses are operating in U.S. cities, he estimates, and new orders suggest that number could rise to 3,000 in a couple of years.

But transit buses are a thin slice of the heavy-duty vehicle market. For the huge number of school buses, non-public transit buses and garbage, utility, and delivery trucks, the news is not good. “Somehow these need to be more strongly supported to get [hybrid] technology to where it can support itself,” says Bartley.

Indeed, such buses and trucks represent a significant untapped opportunity for fuel savings. For example, while hybrid buses consume about 20 percent less fuel, according to Van Amburg, fuel consumption in electrical utility trucks can be reduced by 50 percent with hybrid technology, in large part because, rather than idling the engine at a worksite to power the hydraulic lift used by linemen, the system can be run by batteries, which is much more efficient than idling a large engine. Eaton, based in Cleveland, OH, has already built and tested such a truck, and expects to have 24 of them in operation this year.

An even more immediate impact could come from retrofitting vehicles such as garbage trucks and delivery trucks with hydraulic hybrid systems. While conventional hybrids capture energy from braking and store it in a battery or ultracapacitor, these systems store energy produced by braking by using hydraulic fluid to compress nitrogen gas. The energy in the compressed gas can then be released to power acceleration. Van Amburg says these can be relatively easy and inexpensive to install – an important consideration for a system to be fitted into an already depreciated vehicle.

Currently, several companies are trying out prototype hybrid utility trucks and delivery trucks. But, says Bartley, “It’s not clear you can make a business case for it yet. But I think that, with a little bit more push on the technology and a little bit more economies of scale, we’re reasonably close.”