You seem to be comparing the cost of one additional lane to the cost of a railway. That doesn't seem fair since trains have a much higher capacity than a single lane of a highway. Perhaps I'm misunderstanding?
An HSR is like the Gravina Island Bridge project, aka, Bridge to Nowhere: https://en.wikipedia.org/wiki/Gravina_Island_Bridge
A $400m dollar bridge to replace a ferry for a town of 50 people. Yes, the bridge has a better capacity than the ferry. It still isn't useful because of all the costs associated for so few people.