Abstract: A plastic sideboard for the transportation equipment industry that is lighter in weight than wood or steel sideboards, does not require painting or weatherproofing, will not split or splinter from use, and will not rust, warp, break or bend. The inventive device includes a main board section that may be formed in various heights or than can be stacked to increase overall dump box height, a top rail section that may be rounded to prevent materials from collecting on the top edge, and a bottom rail section that facilitates stable and proper placement of the sideboard into any conventional sideboard bracket. The plastic resin used can be of various chemical components with varying durometers. The plastic sideboard and components may be formed of various color plastics to match the vehicle color.