Hours of Service for the interstate bus driver.

As I understand the ruling from the governments own website, off duty time is, and I quote, "not included in the 15-hour period." And so again, as I understand it, an interstate bus driver can drive a group of some 55 passengers for 5 hours to a particular destination, spend 8-10-12-14 hours (supposedly off duty) hanging out on the bus in some parking lot waiting for his passengers to return, and then spend 5 hours returning them to their point of origin. Sounds like someone was asleep at the wheel when they wrote that rule up. If anyone has a definitive ruling on this, I sure would appreciate knowing what it is .