Are you sure about that? I've never looked up the law, but my understanding is that, for most (all?) of its routes, Amtrak is running on privately owned track, and, on such track, freight has priority.
(I'm surprised at the number of downvotes. The replies indicated that I'm wrong, which is awesome in the sense that I like riding Amtrak and want it to have priority, and so I understand the frustration; but I think that I cannot be the only one who has heard from every Amtrak rider they've talked to that freight has priority, and surely it's a good thing to seek an authoritative answer? Maybe it looked like I was rhetorically saying that someone was wrong rather than honestly seeking clarification.)