The extension may be a sign that the green sticker program hasn't been as effective as expected. As of January, less than a quarter of the 40,000 green stickers that were to be made available had been given out, reflecting what was believed to be a lower-than-expected adoption of plug-in hybrids in the state. In July, Green Car Reports estimated that, in the US, pure electric vehicles outsold plug-in hybrids by about 15 percent during the first half of the year, and those numbers are likely similar in a state with by far the largest number of plug-in vehicles.
California also previously had a yellow sticker program that allowed drivers of hybrids such as the Toyota Prius drive solo in HOV lanes. That program was discontinued in 2011 after the state had given out 85,000 stickers.