Tesla Roadster with CA Clean Air Vehicle sticker -- flickr user jurvetson
No, it's not just because there are too many hybrids in the carpool lane.
New hybrid owners have already been denied those coveted yellow carpool stickers for some time but those with the stickers continue to enjoy driving solo in the carpool lane—for another 15 months, that is.
California's program for single-occupant carpool lane use stickers has been much loved by hybrid drivers, along with the automakers and dealerships that sell hybrids. And in some localities like around the San Francisco Bay or on the 405 in Los Angeles it's hard to miss the constant stream of yellow stickers in the left lane.
But the program has been maligned by both those who actually do carpool in reasonably fuel-efficient vehicles. Opponents also argue that the program has encouraged solo commuters to go out and get a hybrid rather than seek a carpool.
The stickers were created by a 2004 law—AB2628—intended to encourage consumers to purchase hybrids and other advanced-tech vehicles. Although a cap of 85,000 stickers was reached in 2007, the state continues to issue stickers for natural gas or electric vehicles. So far 9,500 of the stickers (white, rather than yellow) have been given out to those types of vehicles.
CA 'Access OK' Clean Air Vehicle carpool lane sticker
The original program was slated to expire in 2008 but was extended to January 1, 2011. The sticker system itself might be extended, but most 'mainstream' hybrids like the Toyota Prius or Honda Insight would not qualify for a revised future system, according to the LA Times.
Any hybrid that gets a combined fuel economy of more than 45 mpg was eligible for the original program. Competing bills to extend the sticker program would either up that mileage cutoff to 65 mpg or exclude gasoline-electric hybrids altogether, only allowing those that use natural gas, other alt fuels, or electricity alone.
To see which vehicles did qualify, consult the California Air Resources' list of eligible vehicles.