About the Green Rating

What is the Green Rating?

The Green Rating measures a vehicle's environmental friendliness on a scale of 1 to 100. The higher a vehicle's Green Rating, the "greener" it is and the lower its harm to both human health and the health of the planet.

The Green Rating was developed by Yahoo! Autos in consultation with Environmental Defense, a leading nonprofit that finds practical ways to protect the planet. The Green Rating covers all the major environmental costs of a motor vehicle, including:

• Unhealthy smog that comes from tailpipes.
• Emissions of greenhouse gases that cause global warming.
• The fuel a vehicle consumes.
• Pollution from manufacturing the vehicle and its components.

More and more car shoppers care about how their choices affect the planet. Yahoo! Autos' Green Rating makes it easy for anyone to comparison shop with the environment in mind.

Because all vehicles -- sedans, coupes, vans, SUVs, trucks, etc. -- are rated on a single 1 to 100 scale, you can use the Green Rating to find the most environmentally friendly vehicle that meets your needs. For example, a 3-point gain in Green Rating between SUVs that score 40 and 43, cuts pollution just as much as a 3-point Green Rating gain between compact cars that score 60 and 63.

You might already look at fuel efficiency when you compare vehicles. But since the Green Rating also reflects tailpipe emissions and other factors, it simplifies the task of weighing the many aspects of a car's environmental friendliness. Some car shoppers think that they need to buy a hybrid, use an alternative fuel or buy a small car in order to buy green. While such vehicles can indeed tread more lightly on the planet, the Green Ratings can help you make a greener choice no matter what kind of car you choose.

How are the Green Ratings derived?

Automobiles degrade the environment in many ways. Because vehicles stay on the road a long time, the largest effects occur during driving. Car pollution includes greenhouse gases, which cause global warming, and smog-related emissions, which trigger asthma attacks and raise the risks of heart and lung disease. Pollution also occurs when vehicles and their parts are manufactured, and again when a vehicle is scrapped at the end of its life.

A vehicle's total environmental impact

A scientific method for adding up all of the environmental damages associated with a product is known as lifecycle assessment. The Green Ratings were developed following principles of lifecycle assessment, using publicly available information to evaluate all vehicles uniformly. Thus, the ratings represent "apples-to-apples" comparisons between different makes and models. The Green Ratings rely on government-certified data and do not consider marketing assertions, "promises," or other unverifiable claims about environmental friendliness.

Major pollutants covered in the ratings include:

• Greenhouse gases, primarily carbon dioxide (CO2)
• Fine particles (particulate matter, PM)
• Nitrogen oxides (NOx)
• Hydrocarbons (HC)
• Carbon monoxide (CO)

These pollutants are emitted from tailpipes as well as during the production and distribution of fuel. Environmental impacts from auto manufacturing are incorporated by basing part of the Green Rating's derivation on a vehicle's weight.

Scientists evaluate car pollution in two broad categories: greenhouse gases that cause global warming (such as CO2) and emissions that directly harm human health (such as PM, NOx, HC and CO). The Green Rating gives equal importance to these two categories. A vehicle's global warming pollution depends largely on fuel consumption, so it is calculated from fuel economy data. A vehicle's health-harming pollution depends largely on the emissions standard that it meets, which forms the basis for that part of the calculation. In others words, a "green" vehicle is one that is both clean and fuel-efficient.

The data behind the ratings

The data used to derive the Green Ratings are a vehicle's official fuel economy numbers and emissions standards as certified by the U.S. Environmental Protection Agency (EPA), plus curb weight. Fuel economy and emissions information comes from tests performed by automakers and accepted by the EPA, with a vehicle subject to recall, penalty or withholding of the certification required for legal sale in the United States if the data are found to be false or misleading. Thus, Green Ratings are based on the most accurate and unassailable data available for all cars and light trucks, ensuring fair comparisons among competing models.

Because of concerns that the EPA miles-per-gallon (MPG) numbers overstate the fuel economy that most consumers experience, the agency is updating the way fuel economy ratings are determined. Revised MPG numbers are planned for model year 2008. Pending EPA's revisions, the Green Rating calculations adjust the fuel economy numbers downward. Because the adjustment is applied across the board, it does not bias comparisons among vehicles or types of vehicles relative to the official EPA numbers. This adjustment will be dropped in future model years once revised MPG data become available.