Earlier quoted context omitted.
People always say this, but a) even countries known for good transit like Japan still have a ton of cars for various things, and b) there's no getting around that the money going into self-driving cars vs public transit isn't something that can really be swapped. It's coming from a different place for a different reason. We absolutely could invest into more trains even with the SDC money flowing anyway, it's not like…
A better idea would just be to let drivers pay the real price for the infrastructure they occupy and their negative externalities. Then people would likely not have a issue with public transit.
Not everyone can do that. Many areas also completely lack the public transit infrastructure needed to support a normal life.
E.g., a couple of days ago, I was shocked to learn just how bad the UK public transport system really is, apparently, outside of major metros (https://news.ycombinator.com/item?id=49445286)