Why is a Californian 15x’s more likely to be killed in a road fatality than a Norwegian?

Take two sample sets of California cities.  One group of cities has an average population density of 5,736 people per square mile.  The other group has an average population density of 2,673 people per square mile.  One group of cities experiences 3.2 road fatalities per 100,000 people per year.  The other group experiences 10.5 road fatalities per 100,000 people per year.  How do the stats and groups match up?

City Beautiful Street Grid

City Beautiful Street Grid


The rate of road fatalities in the group that is twice as dense is 1/3 the rate in the less-dense group.  In other words, residents in the less-dense group of cities are 3 times more likely suffer a road fatality than those in the denser group of cities.  This may seem counterintuitive. Shouldn’t the denser cities have higher rates of road fatalities?  Why don’t they?

Norman Garrick has an answer to that question: street networks and street design.  Garrick is Associate Professor of Civil Engineering at the University of Connecticut and Director of UCONN’s Center for Transportation and Urban Planning. Dr. Garrick is also a member of the national board of The Congress for the New Urbanism (CNU) and co-chair of CNUB”s Transportation Task Force.

“One of the most important but least understood aspects of architecture and urban design is the extent to which the design and layout of residential streets determines the character and quality of communities. Some patterns create a sense of neighborhood and community, while others foster feelings of separateness and isolation. Some nurture social activities and children’s play, while others lead to heavy traffic and degradation of the environment.” (Southwick & Ben-Joseph, Streets and the Shaping of Towns and Cities, 1997).

Those are not Garrick’s words, but they’re a good intro to his presentation on “Networks, Placemaking and Sustainablility.”  It answers the questions above and discusses the research conducted on those two groups of CA cities.  Thanks the Congress for the New Urbanism, you can look at Garrick’s slideshow and listen to audio of his presentation.  The links follow.

(PDF Version of Slideshow)

(Audio of Presentation)

Posted on November 26, 2008, in Public Infrastructure, Transportation. Bookmark the permalink. Leave a comment.

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