Some of the eligible cars are surprising. For example, Ford E-350 like this one qualifies for the white sticker as long as it is burning Natural Gas instead of Gasoline.
Even when running the ICE, the Karma is much cleaner and more efficient than a CNG-powered Ford passenger van, but under the rules of the CAL-ARB, that does not matter. One is Gasoline and the other one is CNG and that is all that counts. If someone out there can convert Karma's ICE to run on CNG, we should be able to get access to the HOV lanes on that basis.