Code of Federal Regulations Title 49. Transportation § 49.299.307 Vegetation

(a) Become a fire hazard to track-carrying structures;

(b) Obstruct visibility of railroad signs and signals along the right-of-way;

(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.