Bi-fuel and dedicated natural gas vehicles

Dedicated natural gas vehicles (NGVs) are equipped to run only on natural gas, and perform better than bi-fuel vehicles. Bi-fuel vehicles can run on either natural gas or conventional fuel (diesel or gasoline) because they carry two separate fueling systems. Learn more about natural gas vehicles on the Energy Office alternative fuels page.

Flex-Fuel Vehicles

Flex-Fuel vehicles are those equipped to run on either gasoline or E85. Manufacturers upgrade components coming into contact with fuel, including the fuel tank, fuel lines and injectors, computer system, anti-siphon device and dashboard gauges, to be resistant to corrosion from ethanol. Learn more about E85 at the Energy Office's ethanol page.

Hybrid (Electric, Hydraulic)

Hybrid electric vehicles (HEVs) combine a combustion engine with a battery and electric motor to achieve higher fuel economy. They can be fueled by gasoline, diesel, hydrogen, CNG, or other alternative fuels. The batteries do not need to be plugged in to recharge, as they are recharged using regenerative braking or by using an on-board generator.

Hydraulic hybrid vehicles are largely in research and development stages at this time. This technology uses a hydraulic energy storage and propulsion system (instead of the battery system used in HEVs), capturing and storing most of the energy normally wasted in vehicle braking. This energy is used to help propel the vehicle during the next vehicle acceleration and allows the engine to operate more efficiently. The EPA has developed this technology, and is partnering on demonstrations with these vehicles in delivery fleets such as UPS. Visit the EPA's hydraulic hybrid engine page for more information.

Idle Reduction Technologies and Policies

Idle reduction describes technologies and policies or practices that reduce the amount of time vehicles idle their engines. Reducing idle time saves fuel, engine wear, and money, while reducing emissions and noise. Idle reduction can come in a combination of forms:

·         Behavior Change (Policies and Practices)

Idle reduction can be achieved through rule-making or legislation. Many local governments have passed ordinances to limit idling in municipal fleets or metropolitan areas. School districts have instructed bus drivers to turn off engines to reduce fuel consumption and reduce emissions that negatively effect children's health.

·         Technologies

There are two main types of technologies for trucks and trains:

• Mobile technologies include on-board computer systems that shut off engines after certain time periods and/or run processes (heating, cooling, etc.) on separate generators while the engine is shut off.
• Stationary technologies include those where a vehicle pulls up to a unit and plugs into an external power source.

More information about available idle reduction technologies can be found here.