RCW 46.04.181: Farm vehicle.

"Farm vehicle" means any vehicle other than a farm tractor or farm implement which is: (1) Designed and/or used primarily in agricultural pursuits on farms for the purpose of transporting machinery, equipment, implements, farm products, supplies and/or farm labor thereon and is only incidentally operated on or moved along public highways for the purpose of going from one farm to another or between locations supporting farming operations; or (2) for purposes of RCW 46.25.050, used to transport agricultural products, farm machinery, farm supplies, or any combination of these materials to or from a farm.