What did Jane Jacobs see on the sidewalk that city planners missed?

She saw that a lively sidewalk is a safety system and a lifeline for a neighbourhood, and that the planners' renewal schemes threatened it. Jane Jacobs, a writer with no college degree or formal planning training, published The Death and Life of Great American Cities in 1961. It was a critique of 1950s planning policy, which she held responsible for the decline of many city neighbourhoods.

Her story starts in Boston's North End in 1959. She found it friendly, safe, vibrant and healthy, while elite planners and financiers called it a terrible slum in need of renewal. The planners' ideal was a city of towers in parks, like Le Corbusier's Radiant City. Jacobs thought they had misread what makes cities work.

Her answer is the sidewalk. Cities are full of strangers, so the challenge is to make people feel safe among them. A healthy sidewalk does it without constant police surveillance, through a network of voluntary controls among the people themselves. She wanted plenty of stores, bars and restaurants along the sidewalks, and buildings facing the street, to keep "eyes on the street" at all hours. Empty corridors and stairwells in high-rise housing, by contrast, are shielded from public view and become flash points for trouble.

So she asked for the opposite of what planners did: dense mixed-use development, short blocks, old buildings alongside new ones, walkable streets, and preserving existing communities. She also fought Robert Moses's Lower Manhattan Expressway, and she was arrested in 1968 at a public hearing on it. The expressway was eventually cancelled.

Her ideas later drew criticism too, including that she left out race and endorsed gentrification, a story we return to later on this path.