One hot summer day I walked through an old, neglected neighborhood, the kind of place where feral cats stalk mice in the weeds near cracked foundations. I carried a tape measure and clipboard, for measuring the width of the sidewalks, the spacing between trees, the length from the back of the curb to the front of the houses. I was channeling my inner New Urbanist, my desire to practice a primitive form of urban archaeology. I was attempting to discover deeper truths about what makes a city successful.

As an engineer I had designed miles of streets and as a planner helped create hundreds of new lots. Yet I knew that I hadn’t the vaguest notion of how to build a really successful neighborhood. I had assembled developments that were a random collection of homes, each built in isolation from the next. What I wanted to know was what it takes to bind that place together in a way that will endure.

New Urbanism is a civic design movement focusing on that question. It advocates the reforming development practices to support traditional patterns: building close-together homes in slow increments over time and storefronts pulled up to the street instead of buried behind nearly empty parking lots—designing cities and towns for people first and then for automobiles, not the other way around.

Before the automobile, before modern zoning, and before massive central government intervention in real estate markets, cities grew and developed around the dominant transportation technology of the day: a person’s two feet. Cities were scaled to people who walked because most people walked everywhere they went.

We sometimes mistakenly view this approach as primitive, lacking the sophistication that today’s auto-based cities have. In that, we are disastrously wrong. Modern development represents not just a step backward in sophistication but an abandonment of complexity in favor of systems that are efficient, orderly, and dumb.

Traditional development patterns, based around people who walked, emerged through trial and error over thousands of years. Societies learned to build this way by innovating incrementally—expanding on what worked while abandoning what didn’t. The result is a resilient building form finely adapted to people, a pattern that repeats with eerie similarity across continents and cultures.

In contrast, our auto-based development pattern—cul-de-sacs feeding arterial roads emptying into highways—has nowhere near such a history of application and testing. While auto-based development is indeed efficient and orderly, it lacks the intuitive feedback inherent in all emergent systems. It is this unavoidable feedback loop—the pain that comes with failure, tested over centuries that included war and peace, feast and famine, drought and abundance—that makes the traditional development approach so strong and resilient.

This is why I was out measuring sidewalks and setbacks. I was searching for the wisdom of my forefathers. What is the optimum distance between trees on a north/south street? What is the optimum ratio of building height to street width for creating a sense of place? How wide must the sidewalks be to have a good transition between public space and private space? Earlier generations figured all of this out and more because they had one thing our auto-oriented planning will never have: the time to test many different scenarios.

If I had ever asked questions like these as an engineer, the answers, if there were any, would likely have come from a book of standards. Such books would treat the small Minnesota town I live in just like any other city, big or small, warm weather or cold, anywhere in the country. When your goal is to reshape radically an entire continent in a generation, you need that kind of efficiency.

After the Great Depression and World War II, Americans took the following lesson to heart: “As the world’s greatest nation, if we focus our energies and resources on an important endeavor, we can accomplish incredible things.” We had proven it. We proved it again and again in the decades that followed.

As we demobilized the military, we began ramping up a growth machine that would transform the continent. Among a population long deprived of excess, a national consensus took shape in support of auto-based suburban expansion. It seemed like a very American way to experience growth and opportunity while arresting the persistent problems of the city—or so we hoped. We expanded housing programs from the New Deal, added incentives for G.I.’s and others to buy new homes, and began building interstate highways that dramatically reshaped cities. Trade groups and professional organizations standardized the regulatory codes, insurance tables, and financing mechanisms to make it all work.

The early results seemed to confirm our theories. Not only did the economy grow rapidly but prosperity was widely shared. Every time we built a highway, bridge, or interchange and every time we ran a pipe out to a cornfield on the edge of town, we saw positive results. What my fellow Minnesotan Thomas Friedman would later call “the American recipe for success” was established: government financing of infrastructure plus incentives for homeownership equals sustained growth and prosperity. The American Dream.

Or the American myth. Local governments are starting to realize that this system doesn’t work. While it has historically provided federal and state governments with the economic growth they seek, it leaves cities responsible for maintaining vast expanses of roadways and huge service areas on a comparatively limited tax base. That works fine when everything is new and the cost of maintenance is low, but it quickly becomes impossible as systems age.

What makes matters more desperate is that for auto-based development patterns aging is not graceful. While buildings in the traditional development style have a natural interdependency—they line up in a pattern, often share walls, their value is a function of the quality of the public space they front, and so forth—each auto-oriented building is, by design, totally independent. It will have its own parking. Many are fenced off from their neighbors or have ditches or berms in between. This is done, of course, to facilitate efficiency in construction. The result is that each failure becomes a random blight.

Auto-based development patterns follow a now familiar cycle of growth, stagnation, and then rapid decline. During the growth phase, when everything is shiny and new, the affluent move in and enjoy the prosperity of a place on the rise. But as those random failures emerge and things start to decline, those with the means to move on tend to do so, leaving behind cities of dwindling wealth. As the decline steepens, local governments borrow money in the hopes that their revenue problems are simply a temporary cash-flow crunch. The result over decades, however, is an insolvent city with huge debts serving an impoverished population poorly situated to bear the financial burdens of an auto-dependent existence.

We’re now two full generations into this experiment. Ferguson, Missouri, was one of those shiny new suburbs that expanded rapidly after World War II. As it has experienced the growth and decline typical of auto-oriented development, not only has it become much poorer but during the transition the municipality borrowed heavily and spent much of its fleeting wealth trying to maintain its position. Ferguson today is trapped: in 2013 it spent $800,000 paying interest on debt while being able to devote only $25,000 to sidewalk maintenance. There is a reason people in Ferguson might walk in the streets instead of on the sidewalks.

Amid the disruption being thrust upon our local governments, a new national consensus is slowing starting to emerge, one that replaces an anti-city approach with a fresh vision for urban areas. The two most mobile age cohorts in America today, millennials and Baby Boomers, are leaving the auto-oriented suburbs—albeit for different reasons—and flocking to cities and streetcar suburbs, places built on a traditional, walkable framework.

As Joe Cortright documents on the City Observatory website, the probability (relative to all metro residents) that a 25-to-34-year-old lives in a close-in urban neighborhood quadrupled from 1990 to 2010. In the 51 largest metropolitan areas, between 2000 and 2012 the number of 25-to-34-year-olds within three miles of the central business district’s core increased twice as fast as outside it. Meanwhile, according to the Brookings Institution, poverty has grown twice as fast since 2000 in America’s suburbs as in America’s cities.

The central task of the Millennial generation is not going to be expanding the boundaries of our cities but managing their contraction. We must find a way to unwind all of these widely dispersed and unproductive investments while providing opportunities for a good life—a modernized American Dream—in strong cities, towns, and neighborhoods. And we have to do all of this with the drag of large debts and a failed national system for growth, development, and economic management that largely associates auto-based development with progress.

This makes the work of the New Urbanists even more important. They are the ones who have applied the rigor needed to understand how a city really works. What are the nuances that make a neighborhood cohesive? Where do we place public buildings and how do we design them so they are not just functional but make a city wealthier? How do we make “good neighbors,” as Robert Frost might ask, without fences and a large setback?

The knowledge required to build livable, walkable places was once common to all in the same way that today Americans intuitively understand that the parking lot goes in front of the big box store and the fast food is located at the off ramp. We’re slowly recovering this lost knowledge, one measurement at a time. And as we begin to apply again this timeless wisdom, we’re rediscovering that traditional building patterns are not just optimized for buildings, they’re optimized for us.

Charles L. Marohn Jr. is a licensed engineer, professional planner, and president of the nonprofit Strong Towns. His latest book is A World Class Transportation System, available on Kindle. This article was supported by a grant from the Richard H. Driehaus Foundation.

Charles Marohn will be speaking on The American Conservative‘s panel at the Congress for the New Urbanism in Dallas on Friday, May 1. See details about all of TAC‘s CNU plans here: https://theamericanconservative.com/urbs/new-urbs-goes-to-dallas/