I personally dont think there should be an exception for Hybrid drivers, as the main point of the carpool lane incentive is to reduce the amount of traffic/congestion on the road during commutes. Less pollution is a secondary goal, a natural consequence of less cars. The proposed bill in CA attempts to limit the HOV from overfilling by limiting the hybrid HOV users to a set number of decal holders far below the number of 45+mpg cars sold, but if there is no guarantee that buying a hybrid will enable access to the carpool lane, it won't motivate more people to buy hybrid cars anyway.