Depends what you mean by double shift, 2-8 hour shifts, or 2-12 hour shifts? I think you should be able to work 16 hours if you want, but not back to back.
As far as the other question about cameras, I think it should be up to the drivers. Here in Suffolk, it's been proven that a cabbie without a partition gets more in tips then one with a devider because they're able to "connect" more. I know you guys don't have the option, but I think it could be applied to cameras.