And to boot: some of it is easy. You just have to bend one rail segment. Manually (which is doable with basic DIY equipment), or explosively. If you're okay with trying 5 times a large boulder positioned between the tracks where it can't be pushed aside easily has a decent chance of derailing a train. And that is a disaster. The amount of stored power in a train's movement is more than enough to destroy it. When this sort of shit happens by accident, there's usually double, sometimes triple digits dead. Targeted, you could do more. Without a few particular train lines, US oil production would slow to a crawl.

They are also far easier to destroy than to rebuild. Terror attack, and things go back to normal in a matter of hours. Sucks for the 5 people, but the economy is not going to be seriously impacted. With trains, and because there's a lot of cleanup, after which the entire line needs to be checked (and obviously not with a high speed train) a derailed train will take a week or two to fix, more on longer lines. It seems to me that disconnecting small cities in middle America from the train network and make coast-to-coast freight go a LOT slower wouldn't be out of the question for even a small organisation.