The present invention is a bi-parting door system for transit vehicles. It has two doors mounted for movement in opposite directions and a motor for opening and closing them. It has at least one lock having a lock member for locking the doors in a closed position. The lock member is biased toward the locking position and moveable to an unlocking position by an actuator controlled by a control system which also controls the motor. When the doors are closed they experience a biasing force tending to open them and this biasing force is reacted by the lock member to generate a load on the lock member which prevents it from moving as a result of a spurious signal to the actuator. Unlocking of the doors requires a door closing signal to be received by the motor to remove the load from the lock member, as well as an unlocking signal to the actuator. Hence, the doors cannot be opened by any one spurious signal to either the motor or to the actuator.