Low Emission Vehicle (LEV): This is the average vehicle, the minimum that you can legally drive in California.
Ultra Low Emission Vehicle (ULEV): ULEVs are described as 50% cleaner than the average new vehicle for the model year. For those of us looking to buy cleaner cars, this should be the minimum standard to consider when new car shopping.
Super Ultra Low Emission Vehicle (SULEV): SULEVs are 90% cleaner than the average new vehicle for the model year. The Honda Insight falls into this class.
Partial Zero Emission Vehicle (PZEV): To obtain a PZEV rating, a car must meet SULEV standards, have zero evaporative emissions, and have a 15 year, 150,000 warranty. My hubby's new Mazda 3 meets these guidelines, as do the Chevy Cobalt, Saturn Ion, and others.
Advanced Technology Partial Zero Emission Vehicle (AT PZEV): To get this rating, a car has to meet all of the above requirements, plus have advanced technology, such as a plug-in hybrid or an engine that runs on compressed natural gas. [Source: DriveClean]