Abstract: When the air brake line on a semi-trailer is disconnected, a plunger is thrust down through the semi-trailer bottom plate to obstruct access to the semi-trailer hitch pin. Reconnection of the air brake line withdraws the plunger.

Abstract: Highway trailer for hauling cargo has air actuated brakes. Valve mounted on the trailer connected in the air line maintains brake-on air pressure in the line while trailer is parked. Valve has locking handle to inhibit trailer theft.

Abstract: A real time, instant replay time-motion analysis system of work measurement that utilizes computer assisted video techniques to simultaneously record and display an operator at work and the elapsed time for the performance of each elemental step in his work task. An observer provides an input signal each time a step is completed and a subsequent step initiated, thereby causing the display of elapsed time relating to the first step to freeze and a display indicating running time for the second step to be generated. Input relating to interruptions occurring during the work process are manually and audibly provided to the system by the observer. The time related data generated during the study is calculated in a microprocessor, and presented as graphical illustrations on the video monitor during replay of the recorded information.