Oregon Revised Statutes Oregon Vehicle Code § 801.140

“Balance trailer” means every trailer, other than a self-supporting trailer, pole trailer or semitrailer, designed so that its weight and that of its load is substantially balanced upon its axle or axles and so that it couples to the towing vehicle with a device other than a fifth wheel hitch. The definition in this section is based upon design features and, except as otherwise provided in this section, does not prohibit a balance trailer from fitting into another classification of trailer based on use.