What is a Low Emission Vehicle (LEV)?

A low emission vehicle (LEV) is one that emits reduced greenhouse gas emissions compared to others of a similar type and/or function.  For the purposes of the Buyers’ Guide, an LEV is defined as “within 25% of the best in the class”.
An important point to note is how the style of driving and traffic conditions or usage affects a vehicle’s greenhouse gas emission performance.
Should a vehicle be used predominantly for the type of stop-start traffic that is typical of city driving, then for vehicles of the same size and performance a hybrid may provide the greatest benefit.
Conversely if a vehicle is mostly driven on open roads such as highway commuting, modern turbo-diesel-engine vehicles may often be the best choice.
Other alternative fuels (e.g. LPG, biofuels) have the potential to provide limited greenhouse gas savings; however these require greater understanding and careful management to ensure optimal outcomes.
Hybrid Vehicles
Hybrid vehicles provide significant greenhouse gas savings during stop-start driving conditions due to such features as:
Diesel Vehicles
Diesel engines have an inherently more efficient operating cycle than spark-ignition (petrol) engines.  This results in less fuel energy being consumed to produce the same amount of propulsion energy for the vehicle.
A characteristic of diesel engines is the production of harmful Particulate Matter (or PM).  Although most new diesel vehicles are fitted with a variety of technologies that make them much better than they used to be, they are still not as clean as petrol engines.

As the greater efficiencies of diesel engines are most evident when the engine is operating within a narrow range of speeds, and the PM air pollutants represent a health risk for humans, diesel vehicles are best suited to highway type driving to allow for greater dispersion of the PM into the atmosphere.
Alternative Fuel Vehicles
Liquid Petroleum Gas (or LPG) is the most widely used ‘alternative fuel’ in Australia.  As with all fuel/technology combinations, the best efficiencies are obtained in vehicles designed and constructed to run only on LPG.  Less efficient are dual-fuel vehicles that are able to run on both petrol and LPG, although they can still be marginally more climate-friendly than petrol.  Aftermarket conversions to LPG are the least efficient approach, and can generally be inferior to those supplied by the manufacturer.
Biofuels (such as ethanol and biodiesel) can provide greenhouse gas reductions beyond that available from fossil fuel technologies, however this is not a guaranteed outcome.  The greenhouse gas implications of a fuel are calculated over the entire lifecycle, from the point of extraction (fossil fuels) or growth (biofuels), to the end use in the vehicle.  As a result, biofuels provide a wide range in possible greenhouse gas outcomes, due to variations in the choice of feedstock (or crop), fertilizer usage and the amount of energy needed to convert the feedstock into fuel.  Presently the fuel distribution market does not enable these differences to be discerned by the fuel user, and so the use of biofuels for greenhouse gas reduction purposes is problematic.
Regardless of these complications, ethanol is mostly sold as a 10% fraction of petrol. At this dilution, the greenhouse gas benefit even under the most favorable of circumstances is only slight, and not likely to better that of a drive-style matched hybrid or diesel.
Natural Gas is plentiful in Australia, but to date has not been employed extensively as a transport fuel, either in Compressed (CNG) or Liquefied (LNG) form. Although its’ greenhouse performance looks promising, it would need a massive investment in infrastructure to become a mainstream fuel.