I love the LH books, grew up with them and made sure my kids did too. There are some known inaccuracies in "The Long Winter" but the major themes are not contested. It was a brutal winter and rail activity was shut down. The book is a treasure and I have re-read it so many times. Highly recommended.
In more recent times, there was definitely an aspect to Amtrak travel that was less weather dependent, and to some extent, can still be found. However, this is increasingly less certain. I've enjoyed many a winter excursion on the Wolverine, where driving would have been problematic and airline flights were facing operational challenges. Today, I'm realizing that this bubble, for the most part, doesn't really exist any more, or at least, shouldn't be assumed. There are a host of good reasons why and how. My thoughts on the why and how don't matter, it's more important to adjust expectations.