When it comes to measuring a car's environmental impact, there's more to consider than just fuel economy.

Every year, the American Council for an Energy Efficient Economy (ACEEE) releases lists of the "greenest" and "meanest" vehicles on sale, based on comprehensive environmental ratings.

DON'T MISS: 2014 Smart ForTwo Electric Drive: What It's Like On The Road

The scores are based on fuel efficiency and emissions, as well as estimations of environmental impact from manufacturing, the materials used, and the distribution of fuel.

Topping the list of greenest cars for the 2015 model year was the Smart Fortwo Electric Drive. This was the electric minicar's second year in a row at the number-one spot, although its environmental-impact score rose to 61 (out of 100) from 59 in 2014.

2014 Chevrolet Spark EV - First Drive, Portland, July 2013

2014 Chevrolet Spark EV - First Drive, Portland, July 2013

Electric cars made a strong showing this year, with the Smart edging out two more electric cars for the top spot.

The Chevrolet Spark EV and Fiat 500e came in second and third, respectively. Low sales numbers kept them off the list last year, and each earned a score of 59 this year.

The only non-electric car to crack the top five was the Toyota Prius C hybrid. It took the fourth spot with a score of 57, matching the Nissan Leaf and putting it three points ahead of the sixth-place Prius Plug-In Hybrid.

ALSO SEE: 2015 Ford F-150 Has Lowest Lifecycle Carbon Footprint: Study

The ACEEE also compiles a list of "greener" vehicles representing the top widely available, gasoline model in each major class.

Still, it should look familiar after viewing the other list.

The top three models were the Toyota Prius C, non-plug-in Prius (with a score of 54), and non-electric Smart Fortwo (53).

2015 Fiat 500e

2015 Fiat 500e

At the other end of the scale, the Ram 2500 heavy-duty pickup truck was named the "meanest" 2015 model, with a score of 17.

It was followed by the mechanically-identical Chevy Express 2500 and GMC Savanna 2500 cargo vans (18), and the Bugatti Veyron which--despite a massive 8.0-liter, quad-turbocharged, W-16 engine--managed to stay out of the worst spot with a score of 19.

RELATED: In Just One Year, Electric Cars Have Gotten Cleaner: How'd They Do That?

This split between large trucks and exotic cars continued through the rest of the "meanest" list, which also included both dated body-on-frame SUVs like the Mercedes-Benz G550 and Nissan Armada, and performance cars like the Lamborghini Aventador Roadster and Ferrari FF.

The complete list of "greenest," "greener," and "meanest" rankings--as well as ratings for virtually every 2015 model--will be available on the ACEEE's newly-updated greenercars.org website. Head over there to see how your next potential car purchase stacks up.


Follow GreenCarReports on Facebook, Twitter, and Google+.