AFTER WAITING @ SWITCH, 1 JEEP & 2 MANTRIPS STARTED MOVING IN LINE, JEEP BOOM CAME OFF TROLLEY WIRE CAUSING IT TO STOP, THE FOLLOWING BUS STOPPED AND WAS REAR ENDED BY 2ND BUS WHICH FAILED TO STOP IN TIME. ALL INVOLVED EE EXITED MINE UNDER OWN POWER. 3 EE FROM REARENDED BUS SOUGHT MEDICAL TREATMENT FOR BACK PAIN. NO INJURIES REPORTED IN 2ND BUS.