Random American cul-de-sac jonathanbecher.com |
Today we are traveling back to suburbia to look at cul-de-sacs. What is a cul-de-sac? A cul-de-sac is a dead-end street, not connected to another street, and provides a way in and out. They exist around the world and have existed for thousands of years. (http://www.culdesac.org) In her article for City Lab, "Debunking the Cul-de-Sac," Emily Badger defines cul-de-sacs as, "Sparsely populated roads loop through the countryside in an odd geometry designed around the residential real estate dream of post-war America: a cul-de-sac for every family."
The concept behind cul-de-sacs was to make neighborhoods more safe, private, idyllic. However, research conducted by Norman Garrick, associate professor of civil and environmental engineering at the University of Connecticut and his colleague at the University of Colorado Wesley Marshall, suggests that cul-de-sacs do the very opposite of what they were designed to do. According to Profs. Garrick and Marshall, "We've really been designing communities that make us drive more, make us less safe, keep us disconnected from one another, and that may even make us less healthy." Could it be that these planned suburban pastorals that were meant to slow traffic down and provide a serene sense of community be just the opposite?
Warning: cul-de-sacs may be dangerous for your health news.yahoo.com |
Grid styles thumbnail sketches Courtesy of Norman Garrick citylab.com |
FHA sketches of good and bad street grids Courtesy of Norman Garrick citylab.com |
The Federal Housing Authority participated in the development of tens of millions of new properties, mortgages, and codifying its particular design preferences. Ms. Badger writes, "From the 1950s until the late 1980s, there were almost no new housing developments in the U.S. built on a simple grid." Prof. Wesley Marshall told Ms. Badger,
You hear the idea that a lot of it was just the free market, that's what people wanted at the time...At the same time, a lot of it was that we were starting to require these types of places along the way. It wasn't just that people wanted to live in these types of communities. It was hard for a developer to come in and build anything different from what had been done.
Suburbia by David Shankbone en.wikipedia.org |
That is the fundamental connection between looking back toward older methods of design...We need to remember when we're designing that we're designing for humans, not objects, and not for the movement of these objects. It's about human beings, about humans being able to get from one place to the other.
Davis, California downtown-Top Five Bike-Friendly Town metaefficient.com |
Inspired by Davis, Profs. Garrick and Marshall assemble data on 230,000 crashes (no indication if any involved fatalities), over an eleven year period in twenty-four medium-sized cites in the Golden State. The professors began to divide and categorize street patterns. There are schemes that resemble square grids and others that take on a tree-like appearance with a single trunk and many branches. Some have tributaries and others that have roadways radiating out from a central hub. There are mix-and-match versions and street blocks of varied length, and some "networks that have 45 intersections per square mile (like Salt Lake City) and others that have as many as 550 (Portland, Ore).
Salt Lake City street map landsat.com |
The answer is simple: the surveyed cities were built the old fashioned way-along those demonized grids. While they did not have fewer accidents, just few accidents with fatalities. Profs. Garrick and Marshall realized that collisions between cars, cars and bicycles were occurring at lower speeds on traditional grid networks. From an initial glance, the traditional street grid might seem just the opposite-more dangerous-cars traveling from ever direction, constantly colliding with other. However, what if the traditional street grid was encouraging drivers to slow down and actually pay more close attention? Not likely in Los Angeles, which is laid out on a Spanish grid.
Downtown Portland, Oregon street map eagleeyesmaps.com |
A lot of people feel that they want to live in a cul-de-sac, they feel like it's safer place to be...The reality is yes, you're safer-if you never leave your cul-de-sac. But if you actually move around town like a normal person, your town as a whole is much more dangerous."
Prof. Marshall's statement is the polar opposite of what traffic engineers and home buyers held true for decades. As Emily Badger states, "And it's just the beginning of what we're now starting to understand about the relative advantage of going back to way we designed communities a century ago.
The next step in Professors Garrick and Marshall's analysis was taking the same group of cities and examined all their precisely classified street network; paying close attention to the amount driving associated with them. On average, the professors discovered that "people who live in more spars, tree-like communities drive about 18 percent more than people who live in dense grids. And that's a conservative calculation."
Downtown Palo Alto, California A typical medium size city bookboth.com |
Perhaps what is harder to gauge is the value of just being connected to the places we want to go and to each other. Scott Bernstein's location efficiency information conveys some of this message. Mr. Bernstein has been able to locate foreclosure hotspots, which tend to be in communities with the least location efficiency-"in spread-out subdivisions, where a family already stretched to the limit can go broke driving 10 miles each way for a gallon of milk. Scott Bernstein told Ms. Badger, "You make a terrible mistake if you plan a city in terms of buildings and facilities and parks...and don't look at the space that those things occupy." So true.
In short, cul-de-sacs may seem like idyllic communities to live but are they? The answer is not really, because they are counterintuitive what we understood a hundred years ago. Traditional urban street grids connected people and places. We see this played out in foreclosure rates, the number of miles traveled by car, and traffic fatalities. Prof. Norman Garrick sums it this way, "It's ironic...but the thing is the patterns that we used to use in American cities are patterns that were built over thousands of years. And there's a reason they were built that way."
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