Actually, I think that carpool lanes are mostly a scam. If the reasoning behind carpool lanes is to increase the number of people on the road by reducing the number of cars on the road, then an HOV lane should require two people with drivers licenses and cars. Ie, it should mean that someone who could be driving, is instead not driving. Sorry, mommy and her baby in a child seat doesn't count. Daddy and his car full of the girls jv soccer team doesn't count.
Granted, the point of HOV lanes may be to encourage a variety of behavior, as can be seen with the recent electric car and hybrid car access permits. In that case, I can see "filling gaps in public transportation" would allow for the types of carpool pickup/drop offs that are common for the SF Bay bridge and in DC (pick up a stranger).
Hmm, this NCDOT study gives the following objectives for HOV lanes:
So, #2 and #6 follow my point. Now, #3 might hold for non-driver passengers in the case where you otherwise wouldn't "fill" your HOV lane with those meeting #2,#5 & #6.
Of course, for some people you can just be willing to pay the fine. Which is why I sit in the 3rd lane and watch all the non-carpool cars in the carpool lane.