Washington Revised Code Title 46. Motor Vehicles § 46.44.036. Combination of units--Limitation

Except as provided in RCW 46.44.037, it is unlawful for any person to operate upon the public highways of this state any combination of vehicles consisting of more than two vehicles. For the purposes of this section a truck tractor-semitrailer or pole trailer combination will be considered as two vehicles but the addition of another axle to the tractor of a truck tractor-semitrailer or pole trailer combination in such a way that it supports a proportional share of the load of the semitrailer or pole trailer shall not be deemed a separate vehicle but shall be considered a part of the truck tractor. For the purposes of this section a converter gear used in converting a semitrailer to a full trailer shall not be deemed a separate vehicle but shall be considered a part of the trailer.