RCW 46.61.615: Obstructions to driver's view or driving mechanism.

(1) No person shall drive a vehicle when it is so loaded, or when there are in the front seat such a number of persons, exceeding three, as to obstruct the view of the driver to the front or sides of the vehicle or as to interfere with the driver's control over the driving mechanism of the vehicle.

(2) No passenger in a vehicle shall ride in such position as to interfere with the driver's view ahead or to the sides, or to interfere with his or her control over the driving mechanism of the vehicle.