Fuel consumption and emissions reductions

The hybrid vehicle typically achieves greater fuel economy and lower emissions than conventional internal combustion engine vehicles (ICEVs), resulting in fewer emissions being generated. These savings are primarily achieved by three elements of a typical hybrid design:

1. relying on both the gasoline (or diesel engine) and the electric motors for peak power needs resulting in a smaller gasoline or diesel engine sized more for average usage rather than peak power usage.
2. having significant battery storage capacity to store and reuse recaptured energy, especially in stop-and-go traffic.
3. recapturing significant amounts of energy normally wasted during braking etc. (regenerative braking) This is a mechanism that reduces vehicle speed by converting some of its kinetic energy into another useful form of energy, dependent upon the power rating of the motor/generator;

other techniques that are not necessarily 'hybrid' features, but that are frequently found fuel saving measures on hybrid vehicles include;

1. shutting down the gasoline or diesel engine during traffic stops or while coasting or other idle periods;
2. improving aerodynamics ; (part of the reason that SUVs get such bad gas mileage is the drag on the car. A box shaped car or truck has to exert more force to move through the air causing more stress on the engine making it work harder. Improving the shape and aerodynamics of a car is a good way to help better the gas mileage and also improve handling at the same time.
3. using low rolling resistance tires ; (tires were often made to give a quiet, smooth ride, high grip etc. but efficiency was a lower priority. Tires cause mechanical drag, once again making the engine work harder, consuming more fuel. Hybrid cars may use special tires that are more inflated than regular tires and stiffer or by choice of carcase structure and rubber compound have lower rolling resistance while retaining acceptable grip, and so improving fuel economy whatever the power source.

These features make a hybrid vehicle particularly efficient for city traffic where there are frequent stops, coasting and idling periods. In addition noise emissions are reduced, particularly at idling and low operating speeds, in comparison to conventional gasoline or diesel powered engine vehicles. For continuous high speed highway use these features are much less useful in reducing emissions.

An addition to the hybrid market is the Plug-in Hybrid Electric Vehicle (PHEV). The PHEV usually consists of a gasoline-electric hybrid with increased energy storage capacity (usually Li-ion batteries). It may be connected to mains electricity supply at the end of the journey to avoid charging using the on-board internal combustion engine.

This concept is attractive to those seeking to minimise on-road emissions by avoiding - or at least minimising - the use of ICE during daily driving. As with pure electric vehicles, the total emissions saving, for example in CO2 terms, is dependent upon the energy source of the electricity generating company.

For some users, this type of vehicle may also be financially attractive so long as the electrical energy being used is cheaper than the petrol/diesel that they would have otherwise used. Current tax régimes in many European countries use mineral oil taxation as a major income source. This is generally not the case for electricity, which is taxed uniformly for the domestic customer, however he/she uses it. Some electricity suppliers also offer price benefits for off-peak night users, which may further increase the attractiveness of the plug-in option for commuters and urban motorists.