49 C.F.R. § 213.321 Vegetation.
Title 49 - Transportation
Vegetation on railroad property which is on or immediately adjacent to roadbed shall be controlled so that it does not— (a) Become a fire hazard to track-carrying structures; (b) Obstruct visibility of railroad signs and signals: (1) Along the right of way, and (2) At highway-rail crossings; (c) Interfere with railroad employees performing normal trackside duties; (d) Prevent proper functioning of signal and communication lines; or (e) Prevent railroad employees from visually inspecting moving equipment from their normal duty stations.
Title 49: Transportation
PART 213—TRACK SAFETY STANDARDS
Subpart G—Train Operations at Track Classes 6 and Higher
§ 213.321 Vegetation.