That rail would be nice to have, but it will not yield a decisive difference on the global warming time frame (~20 years).
You could go the Soviet route (had 30 cars per 1,000 people, a lot of train, bus and subway), but do you really want that? Of course, you would want to improve it because Soviet economy was hugely wasteful despite all this. Plus, all the apartment blocks are not going to build themselves, and certainly not without carbon emissions.
This is just a misleading thought framework of discounting any single item as a “decisive” silver bullet. Of course none of them are being talked about as being a silver bullet.
We need a 1000s of bullets fired at changes to avoid even higher costs of climate change on our current path.
Nothing prevents climate change unless we get more intentional and scaled investments in renewable energy and circular green economies.