PEOPLE ARE LINING UP to buy hybrid cars and sport utility vehicles. In the future, refuse fleets could be lining up for hybrid garbage trucks. A couple of projects now are demonstrating refuse trucks with hybrid hydraulic technology that can save fuel and brakes, plus reduce pollution.

Refuse trucks stop and go hundreds of times each day. Every time the throttle is applied to get a vehicle moving, additional fuel is used. When brakes are applied, energy is lost in the form of heat. Regenerative braking can reduce fuel use by recovering, storing and using a large portion of braking energy to assist the vehicle's engine during initial, high-fuel-consumption acceleration.

Regenerative braking is a key feature of most electric and hybrid-electric vehicles. When drivers step on their brakes, heavy — and expensive — battery packs are used to store braking energy that otherwise would have been wasted as heat. However, there is another way to capture braking energy. Hydraulic regenerative braking recovers energy and stores it as high-pressure hydraulic fluid in an accumulator, rather than in a battery.

The typical hydraulic hybrid uses a combination hydraulic pump/motor built into a vehicle's drivetrain. During braking, the pump/motor operates as a pump using braking energy to pressurize hydraulic fluid that is stored in a high-pressure accumulator while slowing the vehicle. During acceleration, the high-pressure hydraulic fluid is fed back through the pump/motor, which then acts like a motor, to supply additional torque so that the engine has to work less and use less fuel.

Besides providing a 25 percent to 35 percent improvement in fuel economy and reductions in emissions and greenhouse gases, hydraulic regenerative braking reduces brake wear. Also, the greater power density of hydraulic systems improves vehicle acceleration.

In hybrid-electric vehicles, batteries eventually must be replaced. On the other hand, the accumulators in hydraulic regenerative braking systems should last for the entire life of the vehicle. While the best fuel economy improvements will occur when hydraulic regenerative braking is designed into new trucks, retrofitted vehicles could see significant improvement as well.

The U.S. Environmental Protection Agency (EPA), Washington, D.C., has led hydraulic research in the United States and is licensing the technology to companies whose goal is to market hydraulic hybrid vehicles. For example, Eaton Corp., Cleveland, Ohio, has developed Hydraulic Launch Assist (HLA). Eaton's HLA system can potentially be used in Class 2B through Class 8 commercial vehicles.

Both Eaton and Dana Corp., Toledo, Ohio, are targeting frequent stop/start applications, including refuse trucks. Recently, Eaton worked with Peterbilt Motors Co., Denton, Texas, to develop a Class 8 hydraulic hybrid refuse truck using the HLA system installed in a Peterbilt 320 chassis. Eaton predicts the system could be production-ready in two to three years.

In early 2005, Dana plans to demonstrate its hydraulic hybrid in a Mack Trucks LE 613 refuse truck. Dana's system is based on the Ballina, Australia-based Permo-Drive Technologies' Regenerative Drive System.

This Mack truck will be demonstrated in the Los Angeles Basin for up to a year and run on liquefied natural gas. The project is sponsored in part by California's South Coast Air Quality Management District (SCAQMD), Diamond Bar, Calif.; the U.S. Army's National Automotive Center, Warren, Mich.; Mack; and Houston-based Waste Management. According to Dana, the system will create fuel and brake-repair cost savings on par with hybrid-electric vehicles. The lifetime cost will be less than one-third of electric-based systems. Dana expects to have a developed and tested product in volume production by 2009.

According to SCAQMD, fleet managers can expect fuel savings of at least 25 percent and can expect to cut brake maintenance in half. These brake and fuel cost reductions could enable the hydraulic-hybrid technology to pay for itself in about two to three years.

With savings like these, why would any fleet manager stop for another technology?