DRIVE: California's Alternative and Renewable Fuel and Vehicle Technology Program

Medium- and Heavy-Duty Vehicles

Medium- and Heavy-duty vehicles account for 16% of the states’ petroleum consumption and 16% of the transportation sector GHG emissions, yet only comprise about 4% of California’s total vehicle fleet. Major vehicle manufacturers are seeing an increase in purchase orders for natural gas- and propane-fueled refuse and drayage trucks, shuttles, and transit buses. School districts have also shown interest in converting their fleets to natural gas and propane. The Energy Commission supports the conversion of fleet vehicles to alternative fuel use and has awarded over $35 million to design, develop and deploy a variety of heavy duty natural gas and liquefied natural gas trucks in Southern California. An additional $10.8 million was awarded to provide public and fleet fueling stations. In the coming year, the Energy Commission will continue to support the deployment of propane medium-duty vehicles and natural gas medium and heavy-duty vehicles.

Below are some definitions of engine technologies relevant to greening medium- and heavy-duty vehicles:

Hydraulic Hybrid

Hybrid refers to a vehicle having more than one power source.  A hydraulic hybrid vehicle uses a fluid rather than a battery to store energy.  As the vehicle begins to slowdown or stop its forward momentum is used to force hydraulic fluid into the accumulator where it is stored under pressure by compressing a gas. The stored pressurized fluid is released as the vehicle accelerates driving a hydraulic motor to help the vehicle accelerate on takeoff.


A microturbine is much like the engine seen on a jet airplane and consists of three parts a compressor, combustion chamber and turbine.  Air from the compressor is fed into the combustion chamber where it is mixed with fuel and ignited.   The combusted gas is then directed through a nozzle cross the turbine blades, spinning the turbine which powers the compressor and turns the compressor shaft.  The mechanical energy from the compressor shaft can be captured to drive an electrical generator or move the vehicle.

Auxiliary Power Unit (APU)

An APU is a portable device which can supply power and climate control to a vehicle to reduce idling.

Cold Ironing

Cold ironing provides shore-side electrical power to a ship at berth while its main and auxiliary engines are turned off. Cold ironing allows emergency equipment, refrigeration, cooling, heating, lighting and other equipment to operate while the ship loads or unloads its cargo.

Truck Stop Electrification

Truck stop electrification provides a parking space allowing truckers to use electrical power to operate on-board equipment such as air-conditioning, heating, or appliances without idling the truck.  In some cases a stand-alone system can provide heating, and cooling directly to the sleeper compartment along with internet and TV connections.

Find out more about our medium- and heavy-duty projects

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