Hybrid Electric Vehicle (HEV)

A hybrid electric vehicle (HEV) is a type of hybrid vehicle and electric vehicle which combines a conventional internal combustion engine (ICE) propulsion system with an electric propulsion system. The presence of the electric power train is intended to achieve either better fuel economy than a conventional vehicle, or better performance.

Modern HEVs make use of efficiency-improving technologies such as regenerative braking, which converts the vehicle kinetic energy into electric energy to charge the battery, rather than wasting it as heat energy as conventional brakes do. Some varieties of HEVs use their internal combustion engine to generate electricity by spinning an electrical generator (this combination is known as a motor-generator), to either recharge their batteries or to directly power the electric drive motors. Many HEVs reduce idle emissions by shutting down the ICE at idle and restarting it when needed; this is known as a start-stop system. A hybrid-electric produces less emissions from its ICE than a comparably-sized gasoline car, since an HEVs gasoline engine is usually smaller than a comparably-sized pure gasoline-burning vehicle (natural gas and propane fuels produce lower emissions) and if not used to directly drive the car, can be geared to run at maximum efficiency, further improving fuel economy.
Source: Wikipedia

Advantages of HEVs
HEV technology decreases emissions
Decreases fuel consumption
Strategic Stepping Stone Technology
Less Life Cycle Cost

However HEV technology, is more expensive than conventional vehicles.
Have more references on the following topics:
Hybrid Technology
Improving Efficiency, Reducing Emissions
Comparison of Current Technologies

External References
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