MOW TAMPER ON MAIN1 TRACK TRAVELING WEST SHOVING A CART, DERAILED THE CART FOULING MAIN 2. S TACLPC119 TRAVELING MAIN 2 EAST BOUND STRUCK THE MOW CART. TRAIN DID NOT DERAIL. NO INJURIES. DERAILMENT IS DUE TO ENGINEERING RESPONSIBILITY MISSING AN OPPORTUNITY TO FIND AND REPAIR THE PUSH CART AFTER POOR CART TRACKING WAS REPORTED BY MACHINE OPERATOR.