So what exactly IS a "green car"?

At both the Los Angeles Auto Show and Detroit Auto Show, you could find the word "green" all over the place. LA has been pitching itself for years as the greenest auto show, with fewer muscle cars and more hybrids, clean diesels, and so forth than any other U.S. show.

Judging from the signs, it appears that carmakers believe the new definition of "green" is a model that gets 30 miles per gallon or more on the EPA highway test cycle. We were curious how many cars exceeded that level.

2010 Toyota Prius

2010 Toyota Prius

2010 Volvo C30

2010 Volvo C30

2009 BMW 335d

2009 BMW 335d

2010 Kia Soul

2010 Kia Soul

Green Mustang?

In fact, Ford plastered big "30 MPG 305 HP" stickers on the sides of the 2011 Ford Mustang V-6 it launched at the Los Angeles Auto Show. Given its substantial horsepower, 30 mpg highway is indeed impressive from any V-6 Mustang (with six-speed automatic).

We're just not entirely sure that the 2011 Ford Mustang is exactly ... green. Especially if you use the acceleration it's endowed with, which the EPA test cycle doesn't.

150 cars over 30 mpg highway

Indeed, for the 2010 model year, there are more than 150 separate models listed as achieving that magic metric, out of the several hundred vehicle-engine-transmission combinations tested by the EPA.

The 30-mpg-plus vehicles range from a trio of 2010 Volvos (the C30,  S40, and V50, all with front-wheel-drive) that sneak in at 20 mpg city, 31 mpg highway to the undisputed mileage champ and greenest car, the 2010 Toyota Prius hybrid (51 mpg city, 48 mpg highway).

Adding city mileage

If we stay at more than 30 mpg highway, but raise the bar to require city mileage of more than 25 mpg, the number of contenders falls from 151 to 61.

The bottom end of that range (yes, the 2010 Prius stays on top) are four cars of three models (the 2010 Kia Soul, 2010 Nissan Versa six-speed, and the discontinued 2010 Pontiac Vibe), all at 26 mpg city, 31 mpg highway.

Raising the bar

Raising highway mileage alone to more than 35 mpg cuts the number sharply, from 151 to just 29. Bottom of that list is the 2010 BMW 335d clean-diesel sedan, at 23 mpg city, 36 mpg highway--hardly the sort of bare-bones high-mileage miser you might expect.

Adding city mileage of more than 25 mpg cuts that still further, to just 23 cars. Just sneaking in is the 2010 Kia Rio automatic, at 27 mpg city, 36 mpg highway.

And if you tighten the screws even further, to city mileage over 30 mpg, you'll have a grand total of exactly eight vehicles to choose from. The most prolifgate of those are the 2010 Smart ForTwo coupe at convertible, at 33 mpg city, 41 mpg highway.

We say: 26 mpg city, 31 mpg highway

So we'd like to propose our own definition of green car: One rated by the EPA at better than 25 mpg in the city, and better than 30 mpg on the highway cycle.

That 2011 Ford Mustang? It may get 30 mpg on the highway, but it's projected to get only 19 mpg in the city.

We'd like to know what you think qualifies a car as "green". Tell us your thoughts in the Comments, below.