WhatGreenCar.com emissions ratings

The WhatGreenCar? rating system expresses a vehicle's lifecycle environmental impact as a score out of 100 ranging from 0 for the greenest vehicles to 100 for the most polluting.

The rating system used by WhatGreenCar? is based on an assessment of the environmental impacts associated with a car's use and manufacture. This includes all aspects of producing and using the fuel - the fuel cycle (primary production, extraction, transportation, refining, and vehicle operation), as well as the vehicle's manufacture, assembly and disposal - the vehicle cycle.

The WhatGreenCar? analysis first quantifies the extent of life cycle emissions arising from the fuel and vehicle cycles (known as an emissions inventory). The air emissions assessed include the EU regulated emissions - carbon monoxide (CO), oxides of nitrogen (NOx), hydrocarbons (HCs) and particulates (PM) - and sulphur dioxide (SO2). In addition, the three main greenhouse gases associated with road transport are assessed: carbon dioxide (CO2) , nitrous oxide (N2O) and methane (CH4).

Next, the WhatGreenCar? analysis conducts an emissions impact assessment - as its name suggests, this quantifies the impacts of the emissions rather than just quantifying the amount of emissions produced. The advantage of this approach is that the varying levels of all the emissions assessed can be combined to produce an overall environmental impact - without this approach it is difficult to know how to compare (for example) a car with high CO2 and low NOx, with a second vehicle that has low CO2 and high NOx.

The emissions impact assessment is achieved by the use of an environmental rating tool first developed by the European Cleaner Drive Programme to assess the impacts associated with the fuel cycle. This rating system uses recognised 'external costs' to establish the relative weight to attach to different emissions - the external costs are values expressed in monetary terms that reflect the overall damage to the environment and to human health. The analysis used by WhatGreenCar? extends the Cleaner Drive method to include vehicle cycle (car manufacture and assembly).

Using the WhatGreenCar? rating system, the level of environmental impacts are expressed as a score between 0-100 - the lower the score, the less the environmental impact (this reverses the Cleaner Drive scores which were higher for lower emission vehicles).

Input data for the WhatGreenCar? rating methodology comes from number of reference sources including: the Vehicle Certification Agency (for vehicle or tailpipe emissions), Concawe/JRC for fuel production greenhouse gas emissions, and numerous academic papers that estimate the emissions produced during the production of materials used for vehicle manufacture. A selection of the most important references is shown below. For a detailed report on the rating methodology adopted by WhatGreenCar?, see the report entitled Life Cycle Assessment of Vehicle Fuels and Technologies, which is available for download from the Ecolane website.

For more information on the analysis used, see the report entitled Life Cycle Assessment of Vehicle Fuels and Technologies, which is available for download.

References Return to top

Just to show you that we have done our homework, here is a list of the main references on which the emissions methodology is based:

Concawe (2005/06) Well-To-Wheels Analysis Of Future Automotive Fuels And Powertrains In The European Context. Report by Concawe, Eurcar and the EU Joint Research Centre, 2005/06.

Daniels E.J., J.A. Carpenter and P.S. Sklad (2004) Automotive Lightweighting Materials. FY 2004 Progress Report. Argonne National Laboratory. Also personal communication.

ETSU (1996) Alternative Road Transport Fuels: A Preliminary Life-cycle Study for the UK, Volume 2, ETSU. London, The Stationary Office.

Funazaki A., K. Taneda, K. Tahara and A. Inaba. (2003) Automobile life cycle assessment issues at end-of-life and recycling. JSAE Review, Volume 24, Issue 4, October 2003, pp381-386.

IAI (2003) Life Cycle Assessment of Aluminum: Inventory Data for the Worldwide Primary Aluminum Industry. International Aluminum Institute, 2003.

IISI (2002) World Steel Life Cycle Inventory. Methodology Report. International Iron and Steel Institute. Committee on Environmental Affaires, Brussels, 2002.

IPAI (2000) Life Cycle Inventory of the Worldwide Aluminum Industry with Regard to Energy Consumption and Emission of Greenhouse Gases. Paper 1 – Automotive. International Primary Aluminum Institute, 2000.

MacLean, H. and L. Lave (2002) Evaluating automobile fuel/propulsion systems technologies. Progress in Energy and Combustion Science 29; pp.1-69.

Mierlo J.V., J-M. Timmermans, G. Maggetto, P. V. den Bossche, S. Meyer, W. Hecq, L. Govaerts and J. Verlaak (2004) Environmental rating of vehicles with different alternative fuels and drive trains: a comparison of two approaches. Transportation Research Part D 9 (2004) 387–399

Rydh J. and M. Sun (2005) Life cycle inventory data for materials grouped according to environmental and materials properties. Journal of Cleaner Production (13) pp.1258-1268.

Schweimer G.W. and M. Levin (2000) Life Cycle Inventory for the Golf A4. Research, Environment and Transport, Volkswagen AG, Wolfsburg, Germany.

Sullivan (1998) Life Cycle Inventory of a Generic US Family Sedan. Overview of Results USCAR AMP Project. Ford Motor Co.

Zamel N. and X. Li (2005) Life cycle analysis of vehicles powered by a fuel cell and by internal combustion engine for Canada. Journal of Power Sources. In press.