Abstract: A self-propelled and contained trailer washing machine, operable by one individual, which machine is comprised of an integrally powered and steerable wheel mounted rigid frame structure configured to straddle the height and width dimensions of a typical over-the-road commercial trailer so that when the washing machine is operator-aligned to straddle a trailer and then driven along the longitudinal dimension thereof, on such a single driven pass the exterior surfaces of the trailer are automatically washably cleaned by the operator first activating a selected material application pump which supplies an operator controlled amount of a suitable fluid cleaning material directed through a spray arch from one of a plurality of tanks mounted within and carried upon the rigid frame structure, followed by operator activation of a set of spaced frame structure mounted laterally adjustable vertical rotary brushes which simultaneously engage and by opposing rotary motion scrub the respective trailer sides concurrent with