A school bus has a hinged stop arm, a bidirectional electric motor operatively connected to the hinged stop arm for pivoting the hinged stop arm between a stored position adjacent the school bus and a deployed position extending outwardly of the school bus, and a motor control module for controlling the bidirectional electric motor. A retainer arrangement is attached to the school bus for retaining the hinged stop arm in the stored position positively and a second control module is operatively connected to the motor control module. The retainer arrangement includes a servo motor and a lock member that is moved by the servo motor between a lock position retaining the hinged arm in the stored position and a release position allowing the hinged stop arm to be pivoted outwardly by the motor. The motor and the servo motor are operated by a common switch. The switch is moved to a first position when the hinged stop arm is in the stored position to move the lock member to the release position and after a predetermined time delay to automatically pivot the hinged stop arm to the deployed position. The switch is moved to a second position when the hinged stop arm is in the deployed position to pivot the hinged stop arm back to the stored position and after a predetermined time delay to automatically move the lock member to the lock position.