Material of all kinds and all permanent structures such as buildings, walls, coal bins, tunnels, bridges, station shelter sheds, standpipes, signal masts, poles, freight platforms, and structures of like character, placed adjacent or contiguous to a track of a railroad by a county, municipal corporation, township, railroad company, other corporation, or person, shall be not less than eight feet in the clear from the center of such track, measured horizontally from the track and such lateral clearance shall be uniformly maintained vertically upward a distance of twenty-one feet from the top of rail, except in cases in which the public utilities commission finds that such placement or construction is impracticable. This section does not apply to structures in existence on August 25, 1927. The commission may prescribe rules and regulations governing all such placement and construction.