The provisions of section 6-2-2 of this chapter shall not apply to any fire engine or fire truck, police car, ambulance, vehicles of the armed forces of the United States of America or Idaho state guard, vehicles used in line of duty by any duly licensed physician, surgeon or nurse, or to any duly authorized emergency vehicle operating in the necessary circumstances, and in all cases shall be equipped with dim headlights and rear light coverings approved by the chief of police of the city, and no other lights shall be used on any such vehicle. (1961 Code)