I saw this post the other day but didn't follow. Ironically, YouTube had other ideas for me because this popped up for me to watch.
https://m.youtube.com/watch?v=7YwZFm3RrFw
It is from the History Channel, and as with anything from them very in-depth. I enjoyed it being that I love the architecture and the story overall. I had forgotten something I read in my much younger days about the Pennsy being the powerhouse that it was. It really was the Railroad of Railroad's and k think this video really states states it clearly.