Derailment

YNP23R-27, DURING HUMP OPERATIONS, OVERSPEEDS OCCURRED IN THE NORTH MASTER. SHQX3006 WAS THE LEADINGCAR, FOLLOWED BY SHQX1167, SHQX3119, AND SHQX3025. THE EXCESSIVE SPEED PREVENTED THE RETARDERS FROMEFFECTIVELY CONTROLLING THE MOVEMENT. IN ADDITION, CONTAMINATION FROM ANOTHER CUT OF CARS CONTRIBUTED TO THE INABILITY TO PROPERLY REGULATE THE MOVEMENT THROUGH THE RETARDER SYSTEM. THE MOVEMENT EXITED THE EAST END OF EAST BOWL TRACK 123 AND CONTINUED EASTWARD TO APPROXIMATELY MP 285. THE UNCONTROLLED MOVEMENT STRUCK THE DISPATCHER-CONTROLLED DERAIL, WHICH WAS IN THE RAISED POSITION. ONLY THE FIRST TWO CARS DERAILED. THE DERAIL FUNCTIONED AS INTENDED AND STOPPED THE MOVEMENT FROM ENTERING THE MAIN TRACK.