I'm not going to disagree with the arguments you are making as they are valid in their own right, but I will point some to some important tradeoffs your post skips over.
First, there is a fundamental tradeoff between location and transportation. Land is not a produced good, it is owned by landlords and its value comes from location.
Transportation makes prime land less valuable and outlying land more valuable, thus it redistributes value outward, allowing people to escape from the thumbs of landlords and buy their own land. Eisenhower's freeway building project and cheap gas is responsible for the American middle class, much moreso than anything FDR did, as people could move out of apartment buildings in inner cities and buy land of their own, due to the improvements in transportation technology.
For those improvements to work, you have to fan out. A rail line isn't going to get it done, but what a rail line can do is transport people to a remote place and then they fan out with roads. That is a good idea for redistributing people if an area is already densely populated and the land is bought in a large circle around the city. Then you hop on a train to take you to nowhere and there you can buy cheap land. But if the built up area is relatively small, you are better off with a network of cheap roads to carry you to where land is cheaper.
Thus the U.S., which has always had smaller cities surrounded by more open space than Europe, got more bang from its buck with roads. But the same network of roads did not have the transformative effect in Europe as it did in the U.S.
What is interesting is the shift to remote work. The internet has made communication another strong rival to location, providing another threat to land values in inner cities. So it could be that in the future, we will not need so many subsidies for transportation but for things like broadband, to help nurture the middle class and allow people to buy land in remote areas.
People - especially landlords -- are very much aware of these dynamics, which is why historically there was great opposition to roads from moneyed interests, as documented by Adam Smith. And why roads are deserving of subsidies, due to all the positive externalities. In the same way, internet infrastructure is deserving of subsidies today. Whether or not rail is deserving of subsidies in the US depends on how large the disk is of expensive land surrounding cities. In the northeast, it is large, and that's why you see rail in the northeast. In most of the U.S., it's not large at all and you can buy affordable land without traveling too far away from work. In Europe, it tends to be large as well.
With the internet, that is only getting better and both road and rail are becoming less relevant as an agent for the promotion of the middle class land ownership. They are still relevant, but I believe the window has closed on dreams of high speed rail connecting cities in the U.S. High speed internet will get the job done faster and easier, if coupled from a large shift to working from home.