Germany also has both reasonable public transport and good accommodation for private vehicles. You can totally find some people who are on the margin between the two and could be persuaded either way relatively easily.

But even granting that part of your argument, I don't see how you can't offset it? You could either be non-specific and just buy enough carbon offsets. Or if you want to specifically offset public transport use, just bribe some people to move to place with better public transport.

Even the mention of more density or less road for people’s private cars will cause a public outcry that will shut the project down. And it takes years if not decades to construct public transport, so that political will has to run through multiple elections.

My proposal was about changing what people do on the margin. And assuming that we can offset behaviour anywhere on the globe. Ie that you can get more people in Germany on public transport to make up for your sins in America.

(Btw, buses don't need much of a change to the road layout.)