I don’t see how it could be made better without having to do billions or trillions of taxpayer-funded upgrades to every road

This seems like a good-faith comment, so I'll try to keep the snark to a minimum. Honestly, when I hear this sentiment, I think that somebody believes that roads are naturally-occurring phenomena. They just sort of... grow? appear? form from the bedrock?

Good lord, no! Roads are highly resource-intensive structures, and roads for cars have a finite lifetime, typically figured in the range of about 30 years before they have to be re-constructed. And that's not counting perhaps several rounds of re-surfacing and maintenance in that span. In fact, Strong Towns often points out that when businesses acquire a capital asset, they have to book the cost of future maintenance as a liability. Municipal governments, by contrast, book roads as an asset, and ignore the future maintenance liability. If they followed GAAP, most cities and towns would be bankrupt. Hence, the reason the American Society of Civil Engineers grades our roads as D+. As a country, we keep building roads that we can't afford to fix.

That is a long way of saying, "We have a backlog of trillions of dollars of maintenance to roads already!" They have to be re-built regularly, anyway, and lots are overdue. One of the major reasons that we can't afford to do it, and the reason that there are so many lane-miles of road to maintain, is cars. The simple geometry of the space needed for cars means that everything has to be far apart in order to fit the roads, and the parking lots, and the drive-thrus in between.

So, we're on the hook for a backlog of trillions of dollars of taxpayer-funded basic maintenance to roads, and we can't afford it. Wouldn't it be better to re-construct our cities and towns—which again, have to be re-constructed no matter what—around more opportunities for walking, biking, or transit? It would be way cheaper. And without all that pavement for cars, we could put things closer together. Walking to the local grocery would be convenient, because the nearest grocery wouldn't have to be 5 miles away, on the edge of town, where land for a parking lot is cheap enough. We could be healthier, stopping by the grocery for a few minutes on the way home a couple of times a week to pick up fresh, healthy ingredients, instead of loading up the car with a pallet of highly-processed food from CostCo every two weeks. We could have better weak ties with neighbors by seeing them from time to time at nearby places, which science shows is critical to addressing our mental health crisis. We could let our children, elderly, and disabled people have independence again. And the buses could be fast and convenient, if they didn't have to go so far and get stuck in private car traffic all the way.

Anyway, I've gone on long enough, but I hope that this is a peek at just how bad our car-based system is, and how it could be made better, and for cheaper.