I have posted many times on suburban sprawl. Is there something wrong with sprawl? After all, it's a model we've been using in this country for 50 years and in many cases quite successfully.
 

The suburban form is much less dense than the urban form. The urban form is a more efficient use of space and public investment yet under the zoning laws in most suburbs, illegal. None of it could be built without locally-approved special districts and variances, if at all. Suburbs are built for cars and urban places are built for people. Graphic: from Retrofitting Suburbia

 
Before I offer my answer, let me better define suburban sprawl. Ellen Dunham-Jones and June Williamson (mentioned previously here), authors of Retrofitting Suburbia, Urban Design Solutions for Redesigning Suburbs, define it as the suburban form because they look at the form it assumes. The suburban form and the urban form differ in several important ways, to quote:

• Suburban form is characterized by buildings designed "in the round" to be viewed as objects set back in a landscape they dominant; in urban form, a clear focus is on the fronts of buildings and how they line up to meet the sidewalk and shape the public space of the street. [Think of the Cisco campus along SH-190 in Richardson, standing alone, and the Firewheel Town Center where you hardly ever notice anything but the fronts.]
   
• The dominant spatial figures in suburban form are private buildings. Public roadways, schools, and parks exist but are rarely treated as dominate spatial figures or outdoor public rooms, as is the case in urban form. [Compare the Wal-Mart and Sams on N Garland Ave to Downtown with its public square.]
   
• Suburban buildings tend to be dedicated to a single use—residential, retail, office, or industrial—while urban buildings are more often mixed in use or may transition in use over the life span of the building. [Compare the industrial buildings in west Garland to the Downtown, which has evolved many times over the last century and is evolving again.]
   
• Suburban form is almost entirely auto dependent, typically involving surface parking lots surrounding buildings, while urban form is not. [People drive from the Wal-Mart to Target, then to Chick-fil-a, and finally to Marble Slab and Starbucks. Compare that to the Town Center where you probably never move your car once parked.]
   
• Suburban roads are often organized in a dendritic pattern with dead ends and culs-de-sac, while urban streets are organized into interconnected networks. [Think of any strange subdivision where you're afraid of getting lost and then the easy-to-find streets Downtown.]
   
• Suburban form tends to be lower-density and evenly spread out, while urban form tends to have a higher net density as well as a greater range of localized densities. This is true for densities measured by population and by building area. [Just study the graphic for a moment.]
   
• Suburban form is predominantly funded by short-term investors interested in volume, such as real estate investment trusts (REITs) and large home-builders, while urban form is more likely to be funded with a combination of short- and longer-term investment vehicles as well as a variety of public-private partnerships.

In the examples above, we can see differences even locally. Our urban examples locally are few. We have the Firewheel Town Center dropped into a green field and the much, much older Downtown. That we've evolved full circle from a Downtown back to a Town Center is not really that coincidental—for the history of mankind, we've built primarily on a scale for humans and only in the last 50 or 60 years have we built on a scale for cars.
 
Drum roll-ll-ll ... So my answer to "What is wrong with suburban sprawl?" There is nothing wrong with it.
 
Suburban sprawl is a product that has brought trillions and trillions of dollars of investment to this country. It's impossible to be "wrong" in the marketplace if your product is so, so successful.
 
So what is wrong?
 
The mistake we as a country have made is mandating sprawl through our zoning laws to the exclusion of the urban form. This is true in virtually all suburbs and, other than the dense downtown, even most large cities. We have given sprawl a monopoly. We've engineered and built for cars instead of people. We've created room for the cars and pushed the people away from one another.
 
Sprawl has indeed worked for half a century but there is a finite limit to its success: we eventually run out of room that can be accessed within a reasonable drive (time) and high energy prices further contract that threshold (expense).
 
In suburb and city, this is becoming evident. Unfortunately, so far most planners and citizens sense something is wrong but they haven't been able to identify it. They're spending lots of time driving in congestion and on more frequent occasions having to think about a second mortgage to keep their cars fueled but they don't have the experience of a time when or a place where it was different.
 
Allowing whichever product the marketplace wants is the simple, self-correcting way to address development. If one is built but is wrong in the marketplace, the other can replace it. If conditions change, the more efficient or preferable (and affordable) form will prevail. Left to the market, urban places would sprout between suburban expanses. The edges between the two will oscillate according to market conditions.
 
I've advocated New Urbanism many, many times but always in the vein of allowing another product to compete. I don't advocate one over the other. I can choose one for myself and you can choose one for you. Our neighbors and friends will do the same.
 
In the simplest terms, sprawl is ideal for introverts and urbanism for extroverts. Why did we ever pass laws that mandated everyone be an introvert?