Urban Planning Explained: Zoning, TOD, and the City

56% of Humanity Lives in Cities — That Percentage Is Rising

The United Nations projects that 68% of the world's population will live in urban areas by 2050, adding 2.5 billion people to cities over the next quarter century. How those cities are organized — where housing, commerce, and industry can locate; how streets are designed; whether transit is viable — is the domain of urban planning. The decisions planners, politicians, and courts make about urban form have consequences that last for generations, as the United States discovered when mid-20th-century planning choices locked in patterns of automobile dependence, racial segregation, and housing scarcity that cities are still trying to undo.

The Euclidean Zoning Revolution, 1926

Modern American zoning was born in a Supreme Court case. In Village of Euclid v. Ambler Realty Co. (1926), the Court upheld Euclid, Ohio's ordinance dividing the village into single-use zones — residential, commercial, industrial — against a challenge that it violated the 14th Amendment's due process protections. Justice Sutherland's majority opinion famously compared apartment buildings in residential neighborhoods to "a pig in the parlor instead of the barnyard."

Euclidean zoning spread rapidly across American municipalities. By the mid-1950s, most U.S. cities had adopted some form of single-use zoning. The effects were predictable:

• Residential neighborhoods became exclusively residential, making walkable errands impossible
• Industrial and commercial uses were segregated to separate zones, requiring automobile travel for most daily activities
• Minimum lot sizes and parking requirements pushed development outward, accelerating suburban sprawl
• Exclusionary zoning — prohibiting multi-family housing in large residential zones — became a tool for maintaining racial and economic homogeneity

Jane Jacobs vs. Robert Moses

The intellectual battle that defined 20th-century urban planning was fought between Jane Jacobs and Robert Moses — though Moses held all the institutional power while Jacobs had only her arguments and her neighbors.

Robert Moses, New York's unelected "master builder" from the 1930s through the 1960s, built highways through existing neighborhoods, demolished hundreds of thousands of homes for urban renewal projects, and constructed superblocks — large housing projects surrounded by open space and separated from the street grid — based on the modernist planning principle that separating pedestrian movement from automobile traffic would improve urban life. The result was the opposite: superblocks eliminated the street-level activity that made neighborhoods safe and economically vibrant.

Jane Jacobs's 1961 book The Death and Life of Great American Cities attacked this logic systematically. Her core argument:

• "Eyes on the street": Safety in urban neighborhoods depends on continuous informal surveillance by residents going about their daily lives — shopkeepers, residents on stoops, pedestrians. Streets must be active to be safe.
• Short blocks: Frequent intersections allow pedestrians to take multiple routes and encounter more uses, generating foot traffic that supports diverse commercial activity
• Mixed uses: Buildings serving different purposes attract people at different hours, ensuring streets are active throughout the day rather than deserted after business hours
• Aged buildings: New construction can only support high-rent businesses; old buildings with lower rents allow the marginal, experimental, and nonprofit enterprises that give neighborhoods vitality

Jacobs succeeded in stopping Moses's proposed Lower Manhattan Expressway, which would have demolished SoHo. Moses's planning legacy was a cautionary tale; Jacobs's framework became the intellectual foundation of new urbanism.

Transit-Oriented Development

Transit-Oriented Development (TOD) applies Jacobs's mixed-use principles at the scale of a transit network. A TOD node typically places high-density, mixed-use development within a quarter-mile (5-minute walk) radius of a rail station or bus rapid transit stop, with density and residential uses tapering outward.

The Upzoning Debate

American cities face a severe housing shortage. Harvard's Joint Center for Housing Studies estimated a deficit of 3.2 million housing units in the United States as of 2024, with the shortage most acute in high-demand coastal markets. The primary policy response — upzoning, or allowing higher-density development by right — is politically contentious.

Minneapolis became the first major U.S. city to eliminate single-family-only zoning citywide in 2040 (effective 2022 under Minneapolis 2040), allowing duplexes and triplexes on all residential parcels. Oregon followed with a statewide law in 2019. California's SB 9 (2021) allows duplexes on single-family parcels statewide. Early research from Minneapolis showed a measurable increase in housing permits and early evidence of rent moderation relative to comparable cities — though the debate over whether supply-side reforms meaningfully reduce rents in high-demand markets continues among urban economists.