RULE 15. EXCESS OVERTIME, TURN-AROUND RUNS.    For the purpose of avoiding payments of excess overtime on turn-around runs in passenger service when any part or leg thereof is over 80 miles, the railroad will be privileged to rearrange runs, combine pools or sets of runs, and may establish interdivisional runs excepting when this may be prohibited by provisions of existing agreements, such runs to be paid for in accordance with the mileage of this schedule but in no case less than the combination of trip rates in effect April l,1929.