Abstract: A cargo trailer safety lock is set forth for securing typical trailer doors of piggy-back type trailers. A first embodiment includes an upwardly biased "U" shaped bracket oriented into a latch position by an "L" shaped spring-like lever secured to a plate attached to an associated railroad car to maintain latching of the trailer doors until removal of the trailer. A second embodiment includes an elongate sliding latch directed upwardly upon positioning of an associated piggy-back trailer onto a freight car into a latch orientation relative to trailer doors associated with a trailer. A third embodiment includes a generally "U" shaped pivotal latch mechanism with upstanding orthogonally oriented legs maintained in a locking position relative to trailer doors of an associated trailer.