Legal Question in Traffic Law in Washington

It depends. RCW 46.61.660 states that no person shall be transported on the outside of a motor vehicle. RCW 46.61.688 (2) (b) states that a person is not required to wear a seat belt if all of the seating positions are occupied but there is no seat belt available for any such seating position. The federal motor vehicle regulations control the configuration of seating in any motor vehicle sold in the U.S., including number of seats, location and restraint systems. If your truck was not manufactured with seats in the truck's bed, then you cannot just decide to install seats in that truck bed yourself because that would violate the truck's seating configuration as approved by the federal government. If you do go ahead with your plan to install any such seats in the truck's bed, you could be exposing yourself to liability and insurance problems if your truck were to be involved in an accident or collision or rollover incident and your self-installed seats came loose from their anchor points or if anyone occupying one of those seats was ejected without wearing any type of seat belt restraint or if your self installed seat belt failed. Besides being a violation of the law, your insurance company might deny coverage for any property damage and/or personal injury of any such passengers riding in the truck bed "seats" who were to be injured in an accident because the seat or seats were never installed as part of the original equipment and vehicle configuration. Therefore, you would be assuming a big potential liability if you go ahead with your plan to install seating in your truck's bed. The law says all passengers riding in a motor vehicle have to use those seats that are in the enclosed passenger compartment of any vehicle, including only the cab of a pick up truck. Good Luck!