It used to be that hybrids such as the Toyota Prius and Honda Civic Hybrid qualified for stickers to drive in the state's high-occupancy-vehic​le (HOV) lanes, and at least 85,000 drivers of such vehicles took advantage of the program from 2005 to mid-2011, when the California Air Resources Board (CARB) instituted stricter regulations and barred their eligibility. Now, only drivers of electric vehicles and plug-in hybrids can travel solo in the lanes if their vehicles meet the state's tough zero-emissions or partial-zero-emissio​ns requirements.

How tough? When the Chevrolet Volt debuted for 2011, CARB barred the plug-in hybrid from its HOV list, forcing General Motors to modify its gasoline engine enough to pass for the 2012 model year.

So far, nearly 5,600 of the new stickers have been issued. Up to 40,000 plug-in hybrids will be offered a green HOV sticker, including the Prius Plug-In, Ford Focus Electric and Fusion Energi, Honda Fit EV and the Volt. An uncapped number of electric vehicles such as the Nissan Leaf, Tesla Model S and Mitsubishi i-MiEV will be awarded white HOV stickers, in addition to some earlier-model electric, natural-gas and hydrogen fuel-cell cars. Both stickers are set to expire in 2015. (A full list of eligible vehicles is here.)

California isn't the only state offering incentives to drivers who get behind the wheel of a green vehicle; Maryland, New York and Virginia also offer single-occupant HOV-lane stickers. However, California has more HOV lanes (roughly 1,400 miles worth) than any other state.