Abstract: A trailer floor assembly includes a pair of longitudinally extending side rails supporting a plurality of self-mating transverse panels. The plurality of transverse panels includes extruded aluminum panels interspersed with roll-formed steel panels at locations where extra strength is desired (e.g., king pin, landing dollies, and rear door). The extruded panels include T-shaped slots in a bottom wall thereof to allow the extruded panels to be fastened to the side rails by fasteners engaging the bottom wall of the panel but not the top wall the panel. The assembly eliminates transverse cross-beams used to support longitudinal panels in the prior art, and thereby provides improved aerodynamics.