It’s generally accepted that more lanes does not equal less traffic, and can often lead to the opposite effect due to the effect of induced demand [1]. I personally believe providing multiple alternative transport options is more effective but obviously that’s a matter of opinion...
Serious question but is there a reason more isn't invested in public transport? I've only ever lived in the UK before Tokyo but America is rich enough I don't see why they can't do what those places do.
The major reason seems to be a lack of cultural support. Despite everything, people still largely dislike the idea of public transit. I read a very good article that said to generate interest, transit must preemptively provide better service... its a catch 22
Simple: sprawl and ultra low density. Public transport thrives in areas where a single bus stop serves hundreds or more of people, but in rural areas it's cost-prohibitive.
The implicit context of this argument is that space is limited and we can't indefinitely expand roads. We almost certainly can indefinitely lay more fiber.
That said, the logic does apply to wireless spectrum, which is a limited resource. If we allocate enough spectrum that people can replace wired connections, there will definitely be significant and unsustainable demand for even more bands.
[1] https://en.m.wikipedia.org/wiki/Induced_demand