I don't think that will be a problem. With property taxes what they are and rising constantly with land values and the number of people already here it should be no problem to pay for the roads. The problem is that growth keeps occurring even when there is not really space for it. They keep trying to cram more and more houses into the suburbs and it's turning things into a mess. I really wish the population density would drop to about what it was in the 1980s. I love the suburban single family home environment and loathe high density cities. I recognize the need for them but a city like New York or London is about the last place in the civilized world I'd want to live.
I do like a big home, but there's no reason it needs to be built like suburbia.
I bought a house recently, which is 10 minutes walk from a few convenience stores, takeaways and about 15 from the actual centre of town walking, less than 5 on a bike. It's a detached house, it has a large garden and driveway, and for a British home it's pretty decently sized (not American size, but those are uncommon here anyway.) It's like this because it was built in the 30's and the environment evolved around it, rather than it being planned as part of a massive estate.
The problem is that you see so many estates where it's literally just identikit house one after another after another. And then nothing but huge Wal-Marts with parking for 1,000 cars to serve them. The whole environment is actually hostile to walking. Many of these surburban neighbourhoods have no cut-throughs, to allow for quick travel, you have to walk around the roads. (This is usually because a fear of alleyways is that they will attract crime, but statistically there's very little evidence for this. And there's no reason the paths have to be small -- they can be large green spaces with footpaths with good visibility.) And even once you leave, you likely walk straight onto a four-lane dual carriageway type road with a 45+ mph speed "limit". Those roads are just unpleasant to walk along. They're loud, polluted, cars kick up stones and other crap, and kinda scary if the footpath is small. Cycling is also often, at best, accommodated by a small painted bike lane, which offers barely any protection to the cyclist compared to cycling in the lane.
These areas are built to be dependent upon the car; if you don't have a car, you pretty much can't live there. The
stroads that link them split up neighbourhoods, and limit pedestrian traffic.
Compare, for instance, Toronto's central single-family homes:
https://www.google.co.uk/maps/@43.678284,-79.3879489,3a,75y,94.49h,93.64t/data=to a modern-ish Colorado single family home sprawl:
https://www.google.co.uk/maps/@40.0486078,-105.2522135,3a,60y,2.97h,86.25t/data=They look more or less the same from the street, but go to the map, and see that in the Toronto case, the houses are built adjacent useful infrastructure; there's light rail (x2), a nearby town centre, a park to walk the dog... Whereas in Colorado, there's... nothing. Well, not unless you get in your car.
That's the problem with suburbia more than anything else. If you have the density, it's self-funding. Think about all of the tax revenue those businesses bring in. The commuter traffic using trains reduces the infrastructure demand on roads. The parks make people feel better about where they live and pollution will be less because people aren't driving everywhere. But it's actually illegal to build places like that area in Toronto in many cities, because zoning laws mean that an area is "just housing" or "just commercial".