Came here to say just this. The HOT lanes in VA were allegedly going to get some of these thermal cameras to catch HOV cheaters, but AFAIK they aren't installed yet (too expensive). Since you have to use an EZPass on those lanes anyway, I'm not concerned about them being able to count occupants - they already know when you're on the road. Also, GP:
After all, who's going to get into a car with a bunch of strangers, and not have a vehicle when they reach their destination?
google "SLUG" - tons of people pick up strangers everyday near the HOV lanes in VA. Drivers get to work quicker, slugs get a free ride and don't have to pay for parking in DC - win-win.
I gooigled "SLUG." Are you referring to the unit of mass, or the shell-less terrestrial gastropod mollusk? And what does it have to do with traffic?