
Little did they know that Earth was her salvation, as the overpopulated civilization they assumed was backwards and prejudice against anything progressive was very advanced in healthcare technology and treatments. Looking back it made sense, for both the reader and the main characters.
Not only were they advanced in healthcare, they were also advanced in population management. With 8 billion people to house, feed, and keep clean it's a big task. One they accomplished by making a big planetary-level cultural transition.
They moved underground.
When it came out in the late 80s this very concept was shocking and most people believed it to be too radical. "Never happen," my own stepdad said when I exclaimed this as the answer (at my ripe, wise age of 13). "People need open space. No one will want to be restricted inside like that." He was very insistent.
Oh how a lot of things have changed, in just a quarter of a century. Yeah, we're not quite to the point of extreme as Asimov's future Earth world, where people are frightened of the "above ground"...but we're well on our way to being comfortable inside for the majority if not our whole day.
A report just came out from the Federal Highway Administration revealing young drivers 19 and younger dropped over 18% to less than half the age segment and people under 30 make up only 22% of drivers since 1998. Adding to this shift, Gartner research firm found 46% of drivers aged 18 to 24 would choose Internet access over a car. Article HERE.
So, if they are not getting drivers license, how are they getting around? Well, studies indicate that almost half are socializing via internet routes (FaceBook, Instant Messenging, Twitter, etc). If they are getting together, it's using the increasing transportation network (subways, transits, and whatnot). The levels of these two factors depends on the size of the city they are located in.

The shift to underground living answers another need of a heavily populated world. Food production. With people living underground, it leaves the surface available for the production to feed billions of people. Fertile ground, which is now used for subdivisions and city blocks, could be enough land to feed areas where agriculture development is unattainable.
This would be an answer to hunger.
I know it'll be centuries before humans are comfortable living underground to the extent of Asimov's future Earth, if they ever get there. And there are mounds of issues to overcome like high earthquake zones and water and waste infrastructure barriers. And some will never feel comfortable in the "mole" environment.
But then again, that's how Asimov's world ended up with Spacers and Earthers, wasn't it?
So, what do you think about the underground concept? Do you think we'll ever to the extent of Asimov's Earth world? Why or why not?