A method of preventing movement of a locomotive while personnel are working on the locomotive. The method includes placing the brakes of the locomotive under the control of a card reading control box, and providing personnel employed to work on the locomotive with identification cards readable by the box. Each worker inserts his or her card in the box before working on the locomotive, and the control box reads the cards and in response thereto maintains the brakes of the locomotive at full service until personnel have left the locomotive and the control box is cleared by workers again inserting their cards in the box or by a master key in the position of an engineer/operator of a locomotive.