Washington Revised Code Title 46. Motor Vehicles § 46.37.215. Hazard warning lamps

(1) Any vehicle may be equipped with lamps for the purpose of warning other operators of other vehicles of the presence of a vehicular traffic hazard requiring the exercise of unusual care in approaching, overtaking, or passing.

(2) After June 1, 1978, every motor home, bus, truck, truck tractor, trailer, semitrailer, or pole trailer eighty inches or more in overall width or thirty feet or more in overall length shall be equipped with lamps meeting the requirements of this section.

(3) Vehicular hazard warning signal lamps used to display such warning to the front shall be mounted at the same level and as widely spaced laterally as practicable, and shall display simultaneously flashing amber light: PROVIDED, That on any vehicle manufactured prior to January 1, 1969, the lamps showing to the front may display simultaneously flashing white or amber lights, or any shade of color between white and amber. The lamps used to display such warning to the rear shall be mounted at the same level and as widely spaced laterally as practicable, and shall show simultaneously flashing amber or red lights, or any shade of color between amber and red. These warning lights shall be visible from a distance of not less than five hundred feet in normal sunlight.