Cul-de-sacs Are Not Always The Right Answer

http://www.citylab.com/design/2011/09/street-grids/124/?utm_content=buffered4b53&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Random American cul-de-sac
jonathanbecher.com

Hello Everyone:

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

The majority of the oldest cities in the United States, European capitals, or even the Roman Empire were typically laid out in neat, tightly connected grids which allowed people to travel about before the invention of the automobile. The American cities of Manhattan, Savannah, New Haven and Washington D.C., are all laid out in this manner.  The common denominator of these communities is, citing Scott Bernstein, president and co-founder of the Center for Neighborhood Technology (http://www.cnt.org), "'location efficiency,' a rough analogue to the idea of energy efficiency that captures the extent to which your job, your grocery store and your favorite pub are all convenient to you."  In a further burst of efficiency, American cities regardless of size built thousands of miles of streetcar lines with the purpose of making the urban grid even more efficient.

Grid styles thumbnail sketches
Courtesy of Norman Garrick
citylab.com

Scott Bernstein told Emily Badger, "It happened everywhere, it happened brilliantly...and we threw it away."  How did we throw it away like yesterday's newspapers? Blame the automobile.  Ms. Badger writes, Americans lost sight of that tightly knit model when we got into cars and began to envision something else: the Garden City."  Not that the Garden City is the "great satan" of urban planning.  Early twentieth century modernist bemoaned overcrowded cities which were equated with pollution, slums, and poverty.  They wanted to banish superfluous streets and give each worker his own garden plot.  Naturally, he would drive there, along large highways, then down a main street which fed into a collector road, leading to a local street before "...pulling into his own private driveway at the end of a cul-de-sac."

FHA sketches of good and bad street grids
Courtesy of Norman Garrick
citylab.com

Noisy and dangerous traffic would not exist because, unless you lived in the cul-de-sac, there was no reason to drive down these secluded streets.  Traditional street grids with busy intersections and hodge podge of apartments, shops, and restaurants be gone. Describing the suburban model Prof. Garrick told Ms. Badger, "It was addressing real problems, but it went overboard,...It took real problems and then made them caricatures for solutions."  Case in point the Federal Housing Authority adopted the cul-de-sac model in publishes technical bulletins in the thirties which portrayed urban street grids as "monotonous, unsafe, and characterless."  The illustration on the left is an example of FHA sketches of neighborhood layouts, labeled "good" and "bad."

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

According to Emily Badger, "The FHA never put it quite this way, but what we were really doing was building communities for cars, not people."  This very different from the way earlier neighborhood were built. scaled to the human body with architectural decorations at eye lever and pedestrian friendly sidewalks. While the human scale has not changed that radically in the last 200 years, this model should still be relevant.  According to Prof. Norman Garrick,

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

Professors Garrick and Marshall's research into street grid plans began in Davis, California. Frequently cited as one of the most bicycle-friendly cities in America, Davis has the nation's highest rate-over 16 percent-of people commuting by bicycle.  Be that as it may, the city also has one of the lowest traffic fatality rate, counterintuitive for traffic engineers who consider bicycling riskier than driving.

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

However, as Emily Badger writes, "The historical trend, though, has generally moved in one direction-toward ever more creative works of geometric art."  During their California research, Profs. Garrick and Marshall eventually concluded that the safest cities had one commonality: "They were all incorporated before 1930."  It was something particular about the way they were designed that made them safer.  The key component was not larger numbers of bikers equalled safer cities, it was the urban design elements that encouraged the cyclists were the same ones that reduced the number of traffic fatalities. How was this possible?

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

According to Prof. Wesley Marshall,

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

Emily Badger adds her own caveat, "This undoubtedly has to do with the fact that the grocery store, your house and your office are probably father apart-and with less direct connections between them-if you live in a subdivision."  Nevertheless, the difference could also be related to the fact that people who live in cities with traditional urban grids have the need to drive in the first place.  Rather, they are able to get around on foot, bike, or use public transit.  This raised the question in Prof. Marshall's head, "does that mean people live in grids are also healthier?" That is for another study.  Sorry be a tease.

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."