" If the goal of HOV lanes is to increase use of mass transit and to increase carpooling, I would say they are very successful."
Unfortunately that goal is not served by allowing people with children in their cars to count. The system only "works" if it causes someone else (another driver) to elect not to drive but instead ride with someone else.
Agreed, but in the general case, I see plenty of people who carpool and use mass transit to take advantage of the HOV lanes. It would be hypocritical not to allow certain cars with more than one person (a parent and child) and allow other cars with more than one person (two adults) simply on the basis that the two adults are both drivers and "probably" would drive separately otherwise.