I know of several non-freeway HOV lanes in California. Do the stickers allow us to drive in those lanes as well? I haven't been able to find any information on this.

I used to live in the San Jose area, where several expressways have HOV lanes.

Now live in LA area, where there are some surface streets with HOV lanes too (Figueroa near USC/downtown LA for example).

Yes, you can use them. It's the private toll roads that you have to pay.

i use mine on trafic meters getting on the freeway also.

Oh Yeah I drive by about 30 cars waiting to get on the 10 at Milliken in the afternoon, and they all look like they want to kill me