Sunday, March 2, 2014

Walkable Neighborhoods: Street block vs. Cul-de-Sac

In a world full of cul-de-sacs, collectors and massive highways it seems we've forgotten one basic premise: people, not cars, need to get where they want to go.  And people don't think in terms of turning radii, average daily traffic and conflict zones.  

People think, "this is where I am and that's where I need to go."  We always have and, likely, always will.  Hash-tag biology. 

Nothing makes it easier for people to get where they want to go than a high-density of highly connected streets. Urban planning academics refer to these as the Link-Node Ratio and Connected Node Ratio.

Cul-de-sac sprawl vs. traditional street grid
Urban history
We habitually connected our streets until the automobile entered the scene.  We see this is older and more walkable parts of American cities. As detailed in recent books including Fighting Traffic: Dawn of the Motor Age in the American City, Walkable City and The End of the Suburbs: Where the American Dream Is Moving - to name a few - once the automobile came into cities we collectively threw 5,000 years worth of urban wisdom out the window.


You're stuck driving further to where you want to be and spending more time traveling, unless you live in Portland, OR. Demographics are changing and more and more young people are opting out of car culture. Many in the old guard of the transportation world still want to design streets to move automobiles as far and quickly (they'll use the phrase "safely and efficiently"as possible.  Their answer is "tributary" streets. If you want to walk or ride a bicycle, it's almost like being on a battlefield.

The good news is that cities have begun to add more and more bike lanes, trails, bicycle boulevards, bike boxes, bike signals and cycle tracks.  The only thing is a dense street grid is the best thing a city can add to enable bicycling - besides a large, traditional university.  Transportation data is often collected on the municipal level, but time-and-time again people who live in the older and more traditionally designed neighborhoods ride their bicycles to work more than those in the suburbs.

Perhaps this is because of personality difference, but scientific correlations show something else: it's the street block structure! 

"Cycle Analysis Zones" results for an unnamed Western U.S. urban area

If it seems obvious ... it's because it is 

The map to the left shows an image from an adopted bikeways plan for a city in the Inner-Mountain western part of the United States by one of the nation's most recognized bicycle planning firms

Can you tell me where the center of the city is at?

The highly sophisticated analysis of this map shows areas of town that are "best suited for capturing large numbers of cycling trips." This intuitively makes sense considering the higher roadway densities and commercial mix of uses closer to the core.  The traditional neighborhood with a high density of four-way intersections makes it more conductive to usefully riding a bicycle or walking.  Of course the barrier between zones 11, 6 and 4 are high-velocity, four-lanes roads that act like fences in a cow pasture.

Looking back as we move forward 

It's difficult to retrofit existing areas because it's expensive and you don't want your home demolished. However, it's a relatively simple technical exercise to think about these principles when designing new sections of town. But it's going to take public support.  Most land developments are driving by the private market and many developers still live by the Federal Housing Commission's 1938 Bulletin stating the grid layout is "monotonous with little character, uneconomical and unsafe."  

We have lived by the words of that Bulletin for almost 80 years and look where it's got us.  Can we continue down this path? If you want to walk or ride a bicycle for a useful trip, you either need to live near the center of town or take your life into your hands while crossing a busy four-lane street.  We used to know how to build cities for people because [nearly] everybody walked. It's time we use some of our old knowledge on how to build cities and connect our streets! Let's make sure we have at least 70 percent four-way intersections.   

And now for some maps ... 

Houston, Texas, was laid out on a grid pattern.
More than 90 percent four-way intersections. 

Topeka, Kansas, has a similar pattern. Over 90 percent four-way intersections.

This little town in Kentucky has a grid, too.  

Austin, Texas,  has a nice grid pattern from the start.  
More than 90 percent four-way intersections.

Portland, Oregon.  Nice small and consistent block structure: 200ft x 200ft.

Buenos Aires, Argentina.  All the way back in the 1700s.  

Vancouver, BC.  They, also, founded their city with a grid pattern.

Melbourne, Australia.  Circa late 1800s.