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Frequently Asked Questions

Carpool Lane


Plug-in Electric Vehicles and Charging:

Visit our new Plug-in Electric Vehicle Resource Center for answers to all your PEV questions.


Vehicle Emissions


Fuel Economy and Environment Label Ratings


Vehicle Technologies & Performance




What cars can use the carpool lane with one passenger?

California law allows single-occupant use of High Occupancy Vehicle (HOVs) lanes by qualifying clean alternative fuel vehicles. Use of these lanes with only one occupant requires a Clean Air Vehicle Sticker issued by the California Department of Motor Vehicles. Visit California's carpool lane eligibility webpage for more information. Learn More >

Are carpool stickers for hybrids still available?

Yellow Clean Air Vehicle Stickers that had been given to hybrid vehicles expired on July 1, 2011. White and Green Clean Air Vehicle Stickers are still available, however, and valid until January 2019. White stickers are available to an unlimited number of qualifying Federal Inherently Low Emission Vehicles (ILEVs). Cars that meet these requirements are typically certified pure zero emission vehicles (100% battery electric and hydrogen fuel cell) and compressed natural gas (CNG) vehicles. Green stickers are available for qualifying plug-in hybrid electric vehicles up to the first 40,000 applicants. Learn more >


What is the Fuel Economy and Environment Label?

The U.S. Environmental Protection Agency and the U.S. Department of Transportation have adopted a new Fuel Economy and Environment Label that is required on all vehicles beginning in model year 2013. The new federal label can help you compare smog and greenhouse gas emissions no matter which vehicle technology type you choose. Learn More >

What is a Smog Rating?

This is a rating for vehicle tailpipe emissions of those pollutants that cause smog and other local air pollution. This information, listed as “Smog” on the Fuel Economy and Environment Label, will be displayed using a slider bar with a scale of 1 (worst) to 10 (best). The scale is based on the U.S. vehicle emissions standards, which incorporate specific thresholds for nitrogen oxide, non-methane organic gas, carbon monoxide, particulate matter, and formaldehyde. For those vehicles that run on electricity, the tailpipe emissions are zero. Learn More >

How can I reduce my car's smog emissions?

There are several things you can do to reduce the smog emissions from the car you are driving now. Learn More >

What is a Greenhouse Gas Rating?

The federal Fuel Economy and Environment Label assigns each vehicle a rating from 1 (worst) to 10 (best) for fuel economy and greenhouse gas (GHG) emissions (i.e., how much carbon dioxide the vehicle’s tailpipe emits each mile). Consumers may note that higher fuel economy is associated with a better GHG emissions profile. Learn More >

How can I reduce my car’s greenhouse gas emissions?

Any time you are using less gasoline, you are releasing fewer greenhouse gases into the atmosphere and therefore, reducing the major contributor to global warming. The Fuel Economy and Environment Label is also a great tool to compare vehicle emission because it provides a rating from 1 (worst) to 10 (best) for fuel economy and greenhouse gas (GHG) emissions right on the window of every new vehicle. Learn More >

What is the difference between Smog and Greenhouse Gas Ratings? Is one more important than the other?

The short answer is that they are caused by different pollutants, and have different effects on the environment. But, both types of emissions are equally important to reduce.

The Smog Rating corresponds to the amount of smog-forming emissions from a car. These emissions consist of nitrogen oxide, non-methane organic gas, carbon monoxide, particulate matter, and formaldehyde, and they cause more localized, immediate pollution. Smog can cause respiratory health problems, inhibit plant growth and cause damage to crops and forests.

Whereas, the Greenhouse Gas Rating is associated with the amount of carbon dioxide that leads to climate change. Greenhouse gas emissions are the chief contributors to global warming, causing a more collective disruption of climate stability, such as warmer oceans, greater temperature extremes, and altered wind patterns. Transportation is also the largest end-use source of greenhouse gases (including direct emissions and emissions from electricity use), and accounts for 45 percent of the net increase in total U.S. greenhouse gas emissions from 1990-2010. Visit the US EPA website for more on Climate Change.

When choosing a new car and comparing Smog and Greenhouse Gas Ratings, it's a good idea to take both into consideration. Comparing vehicles with a combined rating in mind is a good way to determine the overall environmental effect. Learn More >

How does fuel economy factor into ratings?

Consumers may note that higher fuel economy is associated with a better greenhouse gas emissions profile. Each gallon of gasoline you burn creates 20 pounds of CO2. That's roughly 5 to 9 tons of CO2 each year for a typical vehicle. For more information on how climate change is associated with your vehicle, visit

How can the same make and model vehicle have different ratings?

Two cars may look identical, but their engines could be very different. Auto manufacturers certify their vehicles by their engines, which are given a test group number. For example, a vehicle with a manual transmission could have a different test group number and pollute much more than the same car with an automatic transmission. Different technologies can also have a range in greenhouse gas and smog emissions. For instance, not all hybrids have reduced smog emissions. The best way to make sure you are buying the cleanest version of the new car you want is to look at the Fuel Economy and Environment Label.

If buying an older car, you can find the test group number posted on the Vehicle Emissions Control Information label found underneath the hood. Then, look up that number on the test group search and find out the Smog Rating. The higher the rating, the cleaner the vehicle. Learn More >

When I'm at the dealership, how can I tell which cars are cleanest?

That distinction is very easy because the Fuel Economy and Environment Label rates each car's Smog and Greenhouse Gas emissions on a scale of 1 (worst) to 10 (best). You can compare ratings right here before you go to the dealership by visiting the Vehicle Search.

Why aren’t Greenhouse Gas Ratings posted for older vehicles?

The requirement for Greenhouse Gas ratings to be posted on vehicles didn’t come until the passage of Assembly Bill 1229 in 2005. AB 1229 required the California Air Resources Board (ARB) to redesign the Smog Index Label that had been appearing on vehicles since 1998, and include Greenhouse Gas emissions. Now the federal Fuel Economy and Environment Label provides both Smog and Greenhouse Gas Ratings on a scale of 1(worst) to 10 (best) in order for consumers to compare vehicle emissions. Learn More >

Why worry about comparing Smog and Greenhouse Gas Ratings when ALL new vehicles have gotten much cleaner?

Cars have certainly gotten much cleaner over time, however motor vehicles are still a big contributor to smog and global warming. This is because there continues to be a growing number of cars on California's roads driving more miles every year. Right now Californians drive 825 million miles every day – producing 5.4 million tons of smog forming pollutants daily.

With the federal Fuel Economy and Environment Label it is easy to compare emissions of vehicles and choose something cleaner. Buying vehicles with HIGH Smog and Greenhouse Gas Ratings makes a tremendous difference in how much we pollute.

How well do clean technology cars perform? And are they available in different sizes?

There are a variety of advanced technologies that have come to market in rapidly increasing numbers the last few years. Battery electric, plug-in hybrid, hybrid electric, compressed natural gas (CNG), ethanol (E85) flex fuel, clean diesel and cleaner gasoline vehicles are all available to consumers in a range of makes and models. Hydrogen vehicles are on the horizon as well and are expected in showrooms in 2015.

The way these vehicles perform will vary between make and model just as traditional vehicles do. Clean technology vehicles are comparable in power, style, luxury and amenities to traditional gasoline vehicles. And, they have an added bonus of reduced emissions, and usually better warranties and some really great tax incentives. Learn More >

Search what's on the market today.

Is a NEV a viable option for me?

A neighborhood electric vehicle, or "NEV" is a battery electric vehicle that is zero emission, and a great choice for local, low speed transportation. People who drive regularly on streets with speed limits of 35 miles per hour or less, and need to go less than 30 miles on a charge are good candidates for a NEV. NEVs typically have a top speed of 25 miles per hour and are easily charged in a standard 110-volt wall outlet.

Search for NEVs.

Is a CNG vehicle a good option for me? Where and how would I refuel a CNG car?

A compressed natural gas (CNG) vehicle is a great option for many people. They have all the capabilities of gasoline vehicles, with much less pollution and the ability to drive in the carpool lane with just one passenger in California (and some other states). CNG vehicles are also very similar to gasoline vehicles in the method and time it takes to fuel, and have comparable driving range. It’s easy to find fueling stations as well, with more than 200 already in California.

Learn more about CNG vehicles and find fueling stations at the California Natural Gas Vehicle Coalition web site.

Search for CNG vehicles.

Are ethanol cars good for the environment?

This really depends on how the ethanol, or “E85” is made. Typically, E85 vehicles have similar smog-forming emissions and fewer global warming emissions. Also, since the fuel is produced domestically, it helps to reduce our dependence on foreign oil. Learn More >

Search for E85 vehicles.

Find E85 fueling stations.

Are diesel cars coming back?

Growing numbers of "clean diesels" are coming to market, offering improved fuel economy and reduced greenhouse gas emissions compared to gasoline vehicles. While diesels still have room to improve when it comes to smog emissions, they are expected to meet more stringent emission standards over the next few years. Learn More >

Search for diesels.

Is using biodiesel in a diesel car good for the environment?

It depends. Emissions of oxides of nitrogen can increase with the use of biodiesel in a conventional diesel engine. Biodiesel blended with conventional petroleum derived diesel at concentrations up to 20 percent (B20) is currently used in some diesel engines. Using either blended or pure biodiesel in a diesel (compression ignition) engine will reduce emissions of unburned hydrocarbons, carbon monoxide, sulfates, and particulate matter.

Since the feedstock for biodiesel can be domestically produced, it reduces the nation's dependence of foreign oil. Learn More >

Find biodiesel fueling locations.

How can I find out how much my current car pollutes?

If you have a 2000 model year or newer vehicle, you can search your car's Smog Ratings in the Make/Model Search section. Using Smog Ratings is the only way the environmental impact of older vehicles can be compared, since Greenhouse Gas Ratings only became available for 2009 model year vehicles and beyond.


What happened to the terms we used to hear when it came to clean cars, like ZEV, AT PZEV, PZEV, SULEV, ULEV, and LEV?

These terms are the California Air Resources Board’s (ARB) emission standards that are still used in California's motor vehicle regulations. However, the federal Fuel Economy and Environment Label provides a simpler way for consumers to compare vehicles – by a 1 (worst) to 10 (best) smog and greenhouse gas rating system. California's emission standards correspond to a Smog Rating found on the Fuel Economy and Environment Label.

What types of vehicles qualify for incentive money?

Incentives are available for many advanced technology vehicles – from rebates, discounts and tax breaks to free parking and HOV lane perks. Battery electric, plug-in hybrid, hybrid, CNG, hydrogen and others typically qualify for some sort of incentive or benefit. Learn More >

Search incentives.




Find Clean Vehicles

Slide arrows to view vehicles by rating. Rating of seven or higher are the cleanest.

Greenhouse Gas

Smog Rating

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