[AnimalMuppet]

Sure, it's outlawed - in your suburb. It's not a nationwide ban, though. It's not even (I presume) statewide, or even city-wide.

(It may be true that there literally are no municipalities in the US with zoning codes that allow dense neighborhoods, but I would be highly surprised.)

[DoreenMichele]

The New Urbanist movement tried to recreate dense, mixed use, walkable neighborhoods like were the norm in the past. It was an uphill battle. They would take their plans to city hall and get told it could not be approved. They would then carefully scrutinize the zoning laws, rename some roads and other features as something else, rinse and repeat until something resembling their vision could get approved.

In most parts of the US, you can no longer build those dense, walkable, mixed use neighborhoods that make it convenient to live without a car.

[natrius]

It's outlawed in so many places because of the incentives at work. At the edges of a city, greenfield exclusive neighborhoods have a better chance of holding their value than neighborhoods that let people with less money buy homes on less land. Once an economically stratified city is in place, no one can opt out without losing money. Everyone has to opt out together, and the politics of that are the worst.

[brians]

This is a great focusing question.

There was a study a Few years about about which cities and suburbs could be built under their current zoning laws. I remember it showing that Somerville—a dense collection of 3-decker houses near Boston—was completely impossible to build under its current laws. I don’t have the link handy, but happy googling.

[oftenwrong]

http://cityobservatory.org/the-illegal-city-of-somerville/