The invention comprises a set of tubular inflatable bags mounted to the underside of a transport trailer along its lower edge in front of the rear wheel assembly. The bags are pressurized by ram air inflation upon forward motion of the trailer, such that they prevent air from entering the rear wheel assembly and thereby reduce aerodynamic drag. The outer exposed sides of the bags are vertically and horizontally straightened and stiffened by horizontal ribs which are anchored by cords to the trailer. The apparatus gives way without stress when unpressurized at slow speed and when docking to avoid damage.