shaking is also variable and depends on flat spots, tamping, the head of the rail, etc.
perfectly round wheels and perfect welded track would have no vibrations at all.
i'm not trying to say you can't detect a train coming, but factor in how hard it is to feel gorund vibrations when walking on ballast, the possibility of being in a loud or breezy environment, and having a false sense of security from maybe not seeing trains all the time and it can be difficult to know you are going to get hit.
train crews can also have a hard time seeing the person. we sit so high we are looking at a small object in contrast with the dark rail, light ties, and gravel, often at night. a drunk dude passed out on the tracks looks exactly like a trash bag until just before you hit him and we see things and animals on the tracks all the time so there isn't anything a train crew can do about it
good news is you can't get hit by the train unless you are standing in a very specific ten foot wide lane, so just walk to the side lmao