The top 12 greenest vehicles of 2007

2007 Ford Focus: SES
With a $13,995 base price, the Ford Focus enables one to be environmentally friendly without shelling out a small fortune. Ford / Wieck
/ Source: Forbes

You might be surprised to learn that you don't need to drive a hybrid car to do your part for the Earth.

Yes, of the year's 12 most environmentally friendly 2007-model cars — a list dominated by tiny, economical models — six are hybrids. And two gas/electric hybrids —  Toyota Motor's Prius and Honda Motor's Civic Hybrid — are tied for first place.

But half of the cars are just old-fashioned, gas-powered vehicles that happen to be small and efficient, with low emissions.

For new vehicles, the U.S. Environmental Protection Agency, whose data we used to compile our list, issues air pollution scores and greenhouse gas scores, both of which are ratings from 0 to 10, with 10 being the highest. Only the Prius and Civic Hybrid have perfect greenhouse gas scores, but many cars tie for the top ranking on the air pollution scale (no new car has an air pollution score of 10, but several reach 9.5).

To assemble our list, we took the vehicles with air pollution scores of 9.5, then ranked them based on their greenhouse gas scores. Twelve cars got nods for superior environmental friendliness, including the 2007 Toyota Camry Hybrid and the 2007 Ford Focus.

Boasting a $13,995 base price, the Focus, like many of the autos on our list, enables one to be environmentally friendly without shelling out a small fortune. In fact, the average price of a car on the list is $20,000 — down from the $21,000 average price in last year's list — and a non-hybrid Saturn Ion from General Motors will cost you less than $13,000.

Though you will pay a premium price for hybrid technology, the majority of such cars on our list are humble, such as Ford Motor's $19,000 Escape SUV, or are inexpensive stand-alone models, such as the Prius. Luxury hybrids, such as Lexus' $55,000 GS Hybrid sedan, are just now beginning to appear, and nothing on our list has a base price above $35,000.

The EPA bases a car's air pollution score on the vehicle's output of substances that produce smog and cause health problems. The major pollutants in vehicle exhaust include nitrogen oxides and non-methane organic gases, which combine in the presence of sunlight to create smog. Other pollutants include particulate matter, a lung irritant, and carbon monoxide, a poisonous gas.

A car with an air pollution score of 10 would emit none of these pollutants. A car with a score of 9 emits a maximum of 0.02 grams of nitrogen oxides per mile and 2.1 grams of carbon monoxide. A car with a score of 0, the lowest, emits a maximum of 0.9 grams of nitrogen oxides per mile and 7.3 grams of carbon monoxide. (Plenty of trucks and SUVs score 0's.)

The greenhouse gas score reflects the exhaust emissions of carbon dioxide, a greenhouse gas and one of the biggest byproducts of engine combustion. The EPA bases a vehicle's greenhouse gas score on the car's estimated fuel economy and fuel type. The lower the fuel economy, the more carbon dioxide the car emits. The amount of carbon dioxide emitted per gallon of fuel burned varies by fuel type, since each contains a different amount of carbon per gallon.

The average greenhouse gas score is 5. A car with a greenhouse gas score of 10 will emit less than half a pound of carbon dioxide per mile; a car with a score of 0 will emit 1.35 pounds or more.

In determining the entrants on our list, we evaluated only one vehicle per model range: the cleanest one. In other words, we considered Ford Motor's Escape Hybrid SUV for the list, but not the regular, non-hybrid Escape.