The Clean Air Index is based on a score for each pollutant: maximum for very low emissions; zero (or even negative score) for high emissions. The scale is currently based on values which make it very difficult for modern petrol and diesel cars to score highly in this part of the assessment. Such cars cannot compare with those which emit no tailpipe emissions, such as battery electric vehicles.
The Energy Efficiency Index is calculated on a ‘tank to wheel’ basis and represents only the efficiency with which the electrical or chemical energy stored in the car is converted into motion, assuming fixed values for the energy content of fuels like petrol and diesel. Upstream efficiencies (vehicle assembly, sourcing of raw materials etc) and downstream energy usage (recycling, re-use) are not yet considered.
Green NCAP currently assesses vehicles on a ‘tank to wheel’ basis, meaning that it looks only at the products emitted by the car itself when in use. Any ‘upstream’ impact on the environment, such as the gases emitted during the production of the vehicle or its energy source (petrol, electricity etc) are not considered at this time.
Green NCAP looks at three of the most important greenhouse gases: Carbon Dioxide (CO2), Nitrous Oxide (N2O) and Methane (CH4). Other gases emitted by the vehicle which may have a ‘greenhouse effect’ are not measured.
For its laboratory tests, Green NCAP currently uses the same road load data used for legislative testing. A methodology is under development to verify this data.
Green NCAP’s test laboratories measure particulates with a 23 nm (nanometer) cut-off filter, as required by the latest legislative standards. However, such equipment cannot detect the very injurious super-tiny particles which are emitted in large numbers by some vehicles (particularly petrol-engined cars which do not have a gasoline particulate filter). Green NCAP will use 10 nm cut-off filters in the future but, for now, the rating is based on current measurement technology.
A Life Cycle Assessment is a method to estimate the material and energy flows of a car to analyse environmental effects, like Greenhouse Gas emissions, over the entire lifetime of the car from cradle to grave. It is very complex to obtain information on material sourcing and assembly of the vehicle at the beginning of its lifetime and also on recycling or reuse at the end of its lifetime. Green NCAP will be working in the mean-time with ‘tank to wheel’ and ‘well to wheel’ emissions and fuel/energy flows.