Diane Berger has a Chevy Volt plug-in hybrid with green carpool stickers that allow her to legally drive solo in California diamond lanes.

But as the software engineer commutes from the East San Jose foothills to Campbell, she seldom sees other cars with green stickers.

Only 9,022 green decals have been issued -- well below the cap of 40,000 and a far cry from the 85,000 now-defunct yellow stickers issued to owners of cars like the Toyota Prius and Honda Civic hybrids. That perk ended in 2011, partly because state carpool lanes were filling up and federal transportation officials were threatening to withhold federal aid unless traffic speeds improved in those lanes.

An additional 21,770 white carpool stickers have been given out to owners of all-electric vehicles and those running on alternative fuels like compressed natural gas.

But that program has been in place more than a decade and considering there are more than 30 million registered vehicles in the Golden State, those are not huge numbers. With the improving economy, increasingly jammed freeways and the popularity of the yellow-sticker program, the lukewarm response is not what was anticipated.

"I'm surprised so few green stickers have been issued," said Berger, 53 "I didn't buy my Volt because of the sticker, but I didn't hesitate to apply for one when I got the car."

Also surprised by the low number of carpool stickers is Aaron Neargarder of San Jose, owner of an all-electric Nissan Leaf.

"I was expecting there to be a greater demand just so people could use the carpool lane, especially after seeing how popular the Prius became," he said. "I am guessing the cost of the electric and plug-in hybrid is keeping people from buying the cars."

Plug-in hybrids and electric cars can cost up to $10,000 more than the Prius or Civic hybrids, which run on gas but switch to batteries at low speeds or when idling. Plug-ins run entirely on batteries for the first 11 miles or so, then switch over to gas.

"The bar is high to get the coveted stickers," said Pat Tanti of Campbell. "It will be years and a drastic drop in prices before people make the move."

The carpool sticker program will end Jan. 1, 2015, and many think it is unlikely to be extended because of the low demand as well as the push to convert many carpool lanes into toll lanes that solo drivers use for a fee.

But with 40 percent of all plug-in vehicles in the U.S. registered in California, some state officials think demand will increase. The sticker lure, they say, is worth the effort to showcase high-mileage cars that some buyers might otherwise not consider.

"While we certainly like anything that gets people into the showroom, or considering a plug-in type of vehicle, it's more important to have happy customers beyond the carpool lane benefit," said John Swanton of the state Air Resources Board. "The simple fact is that at some point, this incentive is simply not going to be available and the vehicles will sell or not sell on their own merits."

Requests for green stickers increased late last year, with 1,364 mailed in November. That is the most of any month in 2012, and reason for Swanton to say more plug-ins with green stickers will soon be using our freeways.

"I would say by the end of the program, it will be maxed out just like the yellow stickers were," Swanton said.

As for Berger, she hopes the sticker program will be extended beyond 2015, even if it means more cars fighting for space in the diamond lanes.

"I like being able to use the carpool lane when the regular lanes are backed up," she said. "I may not need to every day, but it's nice to have the option when I do."

Contact Gary Richards at 408-920-5335.

STICKER COUNT

Green stickers for plug-in hybrids: 9,022. Limit: 40,000. Expire: Jan. 1, 2015
White stickers for electric vehicles and those running on alternative fuels: 21,770. Limit: None. Expire: Jan. 1, 2015.
Yellow stickers for hybrids: 85,000. Ended July 1, 2011.

Source: Department of Motor Vehicles.