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