Chrome exhaust pipeEnlarge Photo
Most of the acronyms definitions below come courtesy of the Environment Protection Agency (EPA) and/or the California Air Resources Board (CARB). They apply largely to model years through 2017; classifications will be modified for 2018.
Vehicles manufactured for sale in California and the other states that have adopted its emissions rules often have longer warranties on emissions control equipment, and are manufactured to slightly different standards than the same vehicle sold elsewhere.
California law also requires a lower sulfur content for gasoline sold in California. These rule variations mean a car that earns a Partial Zero-Emission Vehicle (PZEV) rating in California might be classified as a Super Ultra-Low Emissions Vehicle (SULEV) in another state.
National Plug-In Day 2012: San Francisco, with 60 Nissan Leafs in front of the Golden Gate BridgeEnlarge Photo
ULEV: Ultra-Low Emission Vehicle. This is a vehicle that meets the California Air Resources Board standard of 0.125 grams per mile of non-methane organic gas and nitrogen oxide (NMOG + NOx). Virtually all hybrids, and even some non-hybrid vehicles sold today, qualify as ultra-low emission vehicles according to the EPA.
SULEV: Super Ultra-Low Emission Vehicle. To qualify as a SULEV, a vehicle must produce emissions 90 percent lower than an equivalent gasoline-powered vehicle. SULEV is a stricter standard than LEV (Low Emission Vehicle) and ULEV (Ultra-Low Emission Vehicle), but not as strict as PZEV (Partial Zero Emission Vehicle).
PZEV: Partial Zero-Emission Vehicle. PZEVs run on gasoline; by definition they must have zero evaporative emissions from their fuel systems and a 15-year (or at least 150,000-mile) warranty on emission system components. They don't necessarily provide higher gas mileage than other vehicles, but they are much cleaner.
PZEV badge on Ford FocusEnlarge Photo
AT-PZEV: Advanced Technology Partial Zero-Emission Vehicle. A PZEV with the ability to run at least some of the time without emissions. Most plug-in electric vehicles qualify as AT-PZEVs.
ZEV: Zero Emission Vehicle. ZEV is both an emissions standard and a program of sales requirements in California. A standard ZEV produces no emissions from its on-board source of power. Battery electric cars like the Nissan Leaf, Ford Focus Electric, Mitsubishi i-MiEV, and Tesla Model S all qualify as zero-emission vehicles. So do hydrogen fuel-cell vehicles, most notably the Honda FCX Clarity sedan.
MPGe: Miles per Gallon Equivalent. MPGe is a method used by the EPA to rate the efficiency of a non-gas powered car in terms familiar to gasoline drivers. It is simply the distance in miles that an electric or fuel-cell vehicle can cover on the same amount of energy--33.7 kilowatt-hours--that's contained in 1 gallon of gasoline.
Because electric vehicles use energy much more efficiently than combustion-engine cars, their ratings are generally 80 to 125 MPGe. For 2017, the 2017 Hyundai Ioniq Electric is the most energy-efficient car sold in the U.S.: it has an EPA rating of 136 MPGe combined.
2017 Hyundai Ioniq ElectricEnlarge Photo
HOV - High-Occupancy Vehicle: This is the formal term in bureaucratese for what's better known as a carpool, a vehicle with more than one person in it. Carpool lanes for multiple riders are known as HOV lanes; zero-emission vehicles get access to those lanes in California and some other states.
Biodiesel - Biodiesel is a form of diesel fuel manufactured from vegetable oils, animal fats, or biological sources, including algae. It is a specific fuel formulation, and by its nature it has ultra-low sulfur content. It is safe and biodegradable but is more expensive to produce than petroleum based diesel fuel, with which it is often blended. Common blends include B2 (2 percent biodiesel), B5, and B20. Most of today's clean diesels are only warranted for up to B5, though some (including the new 2014 Chevrolet Cruze Diesel and a number of diesel heavy-duty trucks) can handle up to B20.
The term "biodiesel" is also sometimes used to refer to recycled restaurant oils and greases. While older diesels from the 1970s through 1990s can be retrofitted to run on these as a fuel, modern high-pressure injection diesels cannot--and the fuels and automotive industries do not consider filtered fryer oil to comply with their specifications.