Summit study shows safer cities have more tightly networked streets

While much of the discussion of sustainability focuses on global issues like climate and resources, Norman Garrick and Wesley Marshall have focused recent research, presented at the 2008 Transportation Summit, on the human problem of fatalities and serious injuries induced by our transportation system.

The remarkable growth in VMT (vehicle miles traveled) is, to many, the clearest marker of the unsustainability of our current transportation system. Since 1945, while the U.S. population has doubled, VMT have grown by a factor of 11! And while VMT growth depends on a troubling expansion of our appetite for fuel and paved land, the trends in traffic fatalities are hardly more encouraging. Since 1970, U.S. traffic deaths per 100,000 have dropped from 30 to 15, and while this is an improvement, it is nowhere near the success had in the Netherlands, where fatalities have decreased from 30 to only 5 per 100,000. Even after the decrease, there are 42,000 traffic fatalities per year domestically.

As Andres Duany noted in his remarks kicking off the summit, comparisons to Europe are often not received well in the United States. In keeping with this, Garrick and Marshall’s study compares the street networks of safer California cities to less safe cities, finding noteworthy differences in the configuration and scale of networks found in the two groups.

In the study, networks are characterized by intersection and node density. The networks are further analyzed based on Stephen Marshall’s descriptions of network configuration, again finding that safer cities have more tightly woven networks. Meanwhile, more tightly networked cities have much higher walking, biking and transit mode shares, as well as population density nearly double that of the less safe cities.


Important stuff

Garrick's presentation was one of at least two at the summit that broke new ground in demonstrating how traditional highly connective urban street networks make people safer. The other was Charlotte DOT director Danny Pleasant's report on a department study that showed fire stations in areas of the city with more compact urban street grids could capably provide service to larger areas with reduced response times. See the presentation here:

With their results just starting to come into focus this fall, it was great for Norman Garrick and Wes Marshall to give summit participants an early peek at this important work. It will make a big impression in the field when peer-reviewed.


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