Abstract: An auto rack car has an improved door locking mechanism for heightened security in auto rack car doors which rely on upper and lower lock assemblies for security. The improved locking mechanism is lightweight and inexpensive and is adaptable for retrofit installation to lock assemblies which are currently in use on auto rack cars. The locking mechanism thus provides a commercially viable means to prevent unauthorized intrusions into the car involving unlocking of an upper lock assembly and subsequent flexure of the door while a lower lock assembly remains locked.