All bus hazard warning strobe lamps must meet the Class 2 requirements of SAE Standard J1318, and may only be used as follows:

(1) School buses may be equipped with a single additional hazard strobe lamp in addition to the eight lamp warning system. Such lamps must:

(a) Be mounted on the centerline of the roof in the rear one-half of the bus.

(b) Be clear and less than eight inches in height.

(c) Not be mounted any closer than six feet from the rear of the bus measured from a vertical plane tangent to the rearmost point of the bus body. However, if the bus is equipped with a roof hatch falling within six feet of the rear of the bus, the strobe lamp may be located directly behind the roof hatch.

(d) Be activated by a switch independent of all other lamp switches. This switch must be plainly labeled and have a pilot lamp that must indicate when the lamp is in operation.

(e) Only be used when the bus is occupied with school children and one or more of the following conditions exists:

(i) The bus is in motion in inclement, sight obscuring conditions, including but not limited to rain, fog, snow, and smoke;

(ii) There is a need to improve the visibility of the bus when stopping, standing, or starting onto a highway;

(iii) There is limited visibility caused by geographic hazards such as winding roadways, hills, trees, buildings, etc.

The strobe lamp must not be activated solely because of darkness.

(2) Municipal transit vehicles (as defined in RCW 46.04.355) may be equipped with a single additional hazard strobe lamp. Such lamps:

(a) May be mounted on the centerline of the roof in the rear one-half of the bus so long as the lamp is clear and less than eight inches in height.

(b) Be activated by a switch independent of all other lamp switches. The hazard strobe lamp switch must be plainly labeled and have a pilot lamp that must indicate when the lamp is in operation.

(c) Only be used when the bus is occupied with passengers and one or more of the following conditions exists:

(i) The bus is in motion in inclement, sight obscuring conditions, including but not limited to rain, fog, snow, and smoke;

(ii) There is a need to improve the visibility of the bus when stopping, standing, or starting onto a highway;

(iii) There is limited visibility caused by geographic hazards, such as winding roadways, hills, trees, etc.

The strobe lamp must not be activated solely because of darkness.