Russian to English Tech/Engineering Transport / Transportation / Shipping Railways

An excerpt from Russian building regulations (SNiP), and the proximity of pipelines to railways:
Расстояние от газопроводов и тепловых сетей до ***начала остряков***, хвоста крестовин и мест присоединения к рельсам отсасывающих кабелей должно приниматься не менее 3 м для трамвайных путей и 10 м для железных дорог.
The first paragraph of this section (4.16) was the angle at which pipelines must cross railways and roads. One thing not clear to me is whether the pipelines are above or below ground (I presume it's the latter).
Multitran gives a large number of possibilities for остряк, but without seeing a picture, I cannot tell which it is.