No owner shall permit the drivers or operators of their buses to remain on duty for a period longer than 10.5 consecutive hours, and, whenever such driver or operator has been constantly on duty for ten and one-half hours, he shall be relieved and shall not be required or knowingly permitted to again go on duty until he has had at least 10 consecutive hours off duty. No driver who has been on duty 10.5 hours, in the aggregate, in any 24-hour period shall be required or knowingly permitted to continue or again go on duty without having had at least ten consecutive hours off duty. No driver or operator shall be required or knowingly permitted to be on duty more than one 144 hours in any consecutive 21-day period, or more than 54 hours in any consecutive seven-day period. (Ord. 2179 §6, 1946).