Figuring out vehicle emissions ratings is like listening to a commencement speech given by a 90-year-old librarian. It makes your head hurt, and you really aren’t sure you understand it, but you know – somewhere in the letters and acronyms, the dull forest of techno-gabble – there’s important stuff to be had. You just have trouble getting your head around it. When it comes to the cars that burn the cleanest, there are two sets of unbelievably confusing ratings to pay heed to. So – buck up, and we’ll try to make it at least a little more understandable. The two exhaust emission rating systems come from the Federal Environmental Protection Agency (EPA), and the California Air Resources Board (CARB). Cars sold in the US must meet the EPA’s guidelines, and cars sold in California, Maine, Massachusetts, New York and Vermont must also meet the CARB requirements. The EPA uses a Tier and Bin method of grading vehicles, Tier meaning the overall requirements and Bin being the vehicle’s clean classification within the Tier. Bins start at 10, which is the least clean, down to 1, for most clean, with 5 being average:

Tier 2, Bin 10: Least clean…
Tier 2, Bin 9-6: Getting cleaner…
Tier 2, Bin 5: Average…
Tier 2, Bins 4-2: Getting even cleaner…
Tier 1, Bin 1: Cleanest, equivalent to CARB’s ZEV standard (see below)

California has chosen an alphabet game to label exhaust emissions, with the idea of making it more consumer friendly. It’s not, in fact, it’s probably more confusing than the federal standards. Currently, CARB is on phase 2 of its requirements, which are set up based on “Emissions Vehicle,” or EV, with an alphabet description tagged onto the front:

LEV-II: Low Emissions Vehicle, meaning least clean…
ULEV-II: Ultra Low Emissions Vehicle, fifty percent cleaner than LEV-II…
SULEV-II: Super Ultra Low Emissions Vehicle, cleaner than ULEV-II…
PZEV: Partial Zero Emissions Vehicle, the same as SULEV but with a near-zero evaporative emissions standard and a 15-year, 150,000 mile warranty on emissions equipment…
ZEV: Zero Emissions Vehicle, which means absolutely, positively, we promise NO tailpipe emissions

For car shoppers who want the cleanest possible vehicle, the reality is that they would shop for SULEV or PZEV cars/Tier 2, Bin 2-4. Most vehicles qualify in Tier 2, Bin 5, so anything lower than 5 is a cleaner-than option. Among the cleanest on the road, according the EPA classification is the 2006 Honda Civic Hybrid, which qualifies at Tier 2, Bin 2 – one Bin higher than even the Toyota Prius. The Prius, meanwhile, comes in at a CARB rating of PZEV, and an EPA rating of Tier 2, Bin 3. Either are basically the cleanest cars you can currently purchase.

You don’t have to shell out for a hybrid to drive clean, however. In fact, many carmakers offer PZEV and Tier 2, Bin 3 or better cars without the hybrid powertrain premium. Smart shoppers with emissions as a priority would do well to take a look at these vehicles, among others. Also, check out the American Council for an Energy Efficient Economy and their Green Car Guide, for more information about choosing a clean-running vehicle:

Small cars:
2006 Chevy Cobalt
2.2-liter engine, PZEV
MPG: 24/32

2006 Volkswagen New Beetle
2.5-liter engine, Tier 2, Bin 2 / PZEV
MPG: 23/32

2006 Ford Focus
2.0-liter engine, Tier 2, Bin 3 / PZEV
MPG: 26/32

2006 Mazda Mazda3
2.0-liter engine, PZEV
MPG: 26/34

Mid-size cars:
2006 Honda Accord
2.4-liter engine, Tier 2, Bin 2 / PZEV
MPG: 24/34

2006 Mazda Mazda6
2.3-liter engine, PZEV
MPG: 24/31

2006 Nissan Altima
2.5-liter engine, PZEV
MPG: 23/29

2006 Toyota Camry
2.4-liter engine, PZEV
MPG: 24/34

SUVS:
2006 Ford Escape Hybrid
2.3-liter engine, Tier 2, Bin 4 / PZEV
MPG: 36/31

2006 Lexus 400h/Toyota Highlander Hybrid
3.3-liter engine, Tier 2, Bin 3 / SULEV-II
MPG: 33/28