Only a few of the hybrids available today are eligible to be driven in the carpool lane in California. The same restrictions have been subsequently placed in New York, too.
The three hybrids eligible are:
California restricts the use to only the cleanest alternative fuel, hybrid, and full-electric vehicles. Which is why Ford and GM are suing to get into the HOV lane in California. Their hybrids don't meet the eligibility requirements.
California restricts access to those hybrids getting 45 mpg or better.