RCW 46.16A.440
RCW 46.16A.440: Private use, single-axle trailers—Reduced license fee.
Private use single-axle trailers of two thousand pounds scale weight or less may qualify for a reduced vehicle license fee described in RCW 46.17.350 (1)(k). To qualify for the reduced vehicle license fee: (1) The trailer must be operated upon public highways; (2) The vehicle license fee must be collected annually for each registration year or fraction of a registration year; and (3) The trailer must be operated for personal use of the owner and not held for rental to the public or used in any commercial or business endeavor.