I can't really speak to the existence of the middle class but I'll just leave this here: "An astonishing fact: 92 percent of Japanese [like many countries including the US] consider themselves middle-class, according to a labor ministry report published in 2019. That seems to clash with another fact: that nearly 40 percent of Japan’s work force is employed on a part-time or temporary basis, earning less and more vulnerable to layoffs than regular company employees."
Anyway, this is interesting: https://resources.realestate.co.jp/rent/what-is-the-average-... A 1K/1DK (1 bedroom) apartment in the Central Six wards of Tokyo averages 106,000Y per month. The other 17 wards average 72,000Y. A 1K/1DK apartment in Saitama (https://resources.realestate.co.jp/rent/what-is-the-average-...) is 49,000Y. That's ~30-45 min by car or 40 min to 1hr by train (according to Google); i.e. kinda sprawly.
I can't find a median wage for Japan, but the average seems to be about 300,000Y per month, meaning that apartment in the Central Six is out of reach, the other wards would be doable, and outside Tokyo proper would be very doable.
In the US, real estate is the dominant store of wealth for a plurality of Americans, which is why we see such fierce opposition to development. Dense accumulations of people affords great economic opportunities which attract more people, but people need somewhere to live, and if the supply of housing is held far below the demand, prices rise and push out people who can't afford said prices. So people who can't afford sufficient housing within commuting range of economic opportunities within their abilities can either A) forgo the benefits of metropolitan living, B) search the fringes of the metropolitan area for places they can afford/are allowed to build, or C) become homeless.
It would be great if we could just nationally eradicate the regulations, ordinances, zoning codes, etc that cities and towns use to prevent development, but I don't think the 10th amendment allows for that kind of law. And without more housing, there will be sprawl.
[0] https://www.rethinktokyo.com/2018/06/06/depreciate-limited-l...
[0] https://youtu.be/TaU1UH_3B5k [1] https://www.houstontx.gov/planning/DevelopRegs/
More money for roads? If the population increases but is pushed to the periphery, requiring new roads to support them, aren't we just digging ourselves in deeper? How does that pay for the existing roads?