A lot of this feels "citation needed". Unlike streets, building software that can scale up is not necessarily more costly - often it means a cleaner architecture that yields benefits from day 1. The examples of cut-and-cover BART and freeway widening are in direct opposition to each other - sometimes we use a cheap construction approach that involves disruption, or an expensive one that reduces it. It's telling that the author doesn't even see anything unusual in the idea that no expense should be spared for the roads, but subways should be built as cheaply as possible.