That was never the point. Instead, the point was that when we require high-speed expressways in our cities, the land requirements blow up insanely and the land is then useful for pretty much nothing else.
Contrast that to Florence which required much lower speeds and therefore could use the land for many useful purposes. Obviously, Atlanta has nodes of high culture elsewhere, but they certainly can't put any of them here.
As for the proportion of how much land use blows up at speed, consider this: at 5 mph, making a right turn requires just a 15' turning radius, which occupies 225 square feet. The largest curves in the Atlanta interchange (the ones for which you don't have to slow down) have a radius of close to 900', which occupies about 810,000 square feet. So to go 14 times as fast (70 instead of 5 mph) you have to occupy 3,600 times as much land.
Euclidian use-based zoning has been the law of essentially every city in the US beginning about a hundred years ago until the rise of form-based codes like the SmartCode mandates that uses be separated: housing into subdivisions, retail into strip centers & shopping malls, and offices into office parks. This means that you have to drive pretty much anywhere. So if you look at the gross density, just the space required for larger streets, collectors, arterials, and expressways guarantees a substantially less compact city. This is exacerbated by the large setbacks required by those ordinances.
This was celebrated by the architects; Frank Lloyd Wright's Broadacre City celebrated the ideal of every home sitting on an acre of land. Contrast that with the Tuscan town of Pienza, Italy, which sits on a bit over 11 acres of land and which contains over 2,000 residents. Just looking at the numbers, Americans would think it must be some horrible slum. But it's such a fabulous place that it attracts close to a million visitors a year, if I recall correctly. It would be completely illegal to build Pienza in countless American towns and cities, and on many counts. In reality, Pienza would probably violate close to 90% of the conditions in a conventional Euclidian code.
Actually, just the opposite is true. When you build in a really compact way, the countryside is never far away... and that makes the real estate more valuable because a lot of people love the idea of living in the city but having access to the country. In Bath, England, for example, you can stand in the center of town and look down the street and see sheep grazing on hillsides a short distance away. In Atlanta and other sprawling places, you could walk for a day and not reach the countryside.
Can you make a living where you're living? If so, that's awesome. Farmers obviously do that; fishermen often live in small fishing villages. Lumberjacks can live in the woods just fine. The problem is when people move to the country but still work in the city, and have to endure the traffic getting around every day.
I live in South Beach, and while we still have a car, we only drive it a couple times per week. The gold standard is being able to walk to the grocery. If you can do that, you can walk to a lot of other things as well.
I'm the author of the original post on originalgreen.org. While the images are sensational and actually went viral a couple years ago, the real message is to point out that the need for speed necessitates massive waste of land and resources. At speeds experienced in Florence, the curb radii of the streets are essentially invisible, whereas the expressway radii each take up much of the Atlanta image. Yet which place provides wonderful experiences? Isn't it time to slow down?
Contrast that to Florence which required much lower speeds and therefore could use the land for many useful purposes. Obviously, Atlanta has nodes of high culture elsewhere, but they certainly can't put any of them here.
As for the proportion of how much land use blows up at speed, consider this: at 5 mph, making a right turn requires just a 15' turning radius, which occupies 225 square feet. The largest curves in the Atlanta interchange (the ones for which you don't have to slow down) have a radius of close to 900', which occupies about 810,000 square feet. So to go 14 times as fast (70 instead of 5 mph) you have to occupy 3,600 times as much land.