Notwithstanding the provisions of N.H. Rev. Stat. § 266:44, the tail lamps and reflectors on trailers may be located at a height of less than 20 inches from the ground, measured from the ground to the center of the vehicle, provided they are placed in such manner as to indicate the extreme width of the vehicle and load, and the visibility of reflectors is not impaired at any time and they reflect rays of light thrown upon such reflectors.