Even for jet travel, we may be able to whittle away at the problem with electric planes (or trains!) for short routes, and hydrogen for medium routes. Long routes may have to rely on artificial carbon-based fuels, as you say.
There are plenty of population centers that aren't densely urban. Cities in the 200k to 400k range seem like they're just starting to be big enough to support a regional bus system on their own, or with the support of a nearby larger city.
The problem is how infrequently they would run though. Those cities tend to sprawl just a bit as they haven't made the full transition to multi-tenant dwellings so lots of folks would have to walk multiple blocks sometimes to get to a stop.
Individually operated vehicles, namely cars, are still the name of the game for the vast majority of America. But then you run into the electrification issues I mentioned. A lot of these neighborhoods have very old electrical systems, and while we've made a ton of room by not running 60W light bulbs everywhere, I'm not sure we could handle charging 50k electric cars per night in many medium sized cities.
You can scale up electrical infrastructure relatively easily (especially compared to installing a subway or cable car system), and it will be a lot more popular politically to upgrade this infrastructure than to force people to use buses.
Obviously, transition to EV is a key necessity for getting transportation off fossil fuels. Now, international jet travel and global shipping are not going to work with electric power due to lower energy density in batteries, but here we can simply do artificial photosynthesis, based on DAC and hydrogen from water, and generate carbon-neutral fuel with no need to sacrifice agricultural land.