A new study shows just how much 20th-century cities have expanded compared to cities built before the automobile.

A persistent spatial pattern exists in pre-automobile cities, following a phenomenon dubbed the "400-meter rule," the maximum distance between intersections of main thoroughfares.

On average, the distance between major intersections in 20th-century cities was twice as large as what can be seen in historic cities.

The researchers, from University of Strathclyde, examined 100 case studies from 30 countries, covering historic urban design from the ancient, medieval, renaissance, baroque, and industrial periods.

"Our conclusion is that the contribution of urban design models to the unsustainable, car-dominated city of today has been, and continues to be, of crucial and indeed generally underestimated importance," the researchers write.

"[B]y better understanding the critical relationships between urban streets and plots, urban designers can begin to repair and develop more adaptable urban tissues," they conclude.

Street Networks Are Twice The Size They Were Before Cars

And that goes for even those cities built according to enlightened urban-planning models.

The last century of city building has been all about sprawl. In the 20th century, especially in the U.S., cities spread out, facilitated by the fact that the widespread adoption of cars made it easy for people to get around. A new study shows just how much cities planned in recent history have expanded. A group of urban designers and architects at the University of Strathclyde in Glasgow find that, for the most part, the main network of streets in 20th-century cities are built on a scale that's twice as large of that of older cities like Paris, Milan, or Calcutta. Their findings have implications for the development of the human-scale communities contemporary for which urban designers are aiming.

The research follows up on a 2010 study claiming that a persistent spatial pattern existed in cities that grew up before the automobile, one that followed a phenomenon dubbed the "400-meter rule," the maximum distance between intersections of main thoroughfares. To test this empirically, researchers at the University of Strathclyde examined 100 case studies from 30 countries, covering urban design from the ancient, medieval, renaissance, baroque, and industrial periods, as well as contemporary cases planned around Ebenezer Howard's Garden City model for a circular community around a central garden, Le Corbusier's "towers in a park" Radiant City model, and the walkable, mixed-use New Urbanism model. They also studied informal settlements around cities like Caracas, Venezuela, and New Delhi, India.

They found that the 400-meter rule held. The scale of historic cities' street networks was rarely larger than 400 meters (around 1,300 feet), with average distances on the range of 300-350 meters. Cities that developed starting in the early 20th century display a much greater range of distances between major intersections, but on average, the distance was twice as large as what can be seen in historic cities. Even those metropolises built on the model of walking-oriented New Urbanism averaged 788 meters between intersections. The exception was the informal settlements, which, lacking formal infrastructure and planning, were built on the smaller scale of older cities.

Though current urban design theory touts neighborhood density and smaller blocks, the researchers note that the compact nature of 18th- and 19th-century cities wasn't always considered an advantage: Industrialization made them overcrowded, polluted, and unsanitary. Models like Le Corbusier's Radiant City, which proposed a linear city of high-rises in the midst of ample parkland, were designed as an antidote to these lackluster conditions. However, these models, and planning with automobile traffic in mind, have clearly had an impact on the scale of our cities, making them more spread out--and thus less accommodating for other modes of transport, like walking.

The researchers write, "Our conclusion is that the contribution of urban design models to the unsustainable, car-dominated city of today has been, and continues to be, of crucial and indeed generally underestimated importance." They call for further research into the logic that governs city design, especially in those historic places that have managed to adapt to hundreds of years of changing conditions. "[B]y better understanding the critical relationships between urban streets and plots, urban designers can begin to repair and develop more adaptable urban tissues, capable of adjusting to changing demographics, economies and cultures over time."

[Image: Grid streets via Shutterstock]

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