Ped Shed

Intersection density is the number of intersections in an area. It corresponds closely to block size — the greater the intersection density, the smaller the blocks. Small blocks make a neighborhood walkable. This diagram shows three street layouts — extremely walkable, moderately walkable, and unwalkable — with their counts of intersections per square mile:

Intersection density makes surprising news in a study by the formidable academic duo of Reid Ewing and Robert Cervero. They have published Travel and the Built Environment: A Meta-Analysis in the Summer 2010 issue of the Journal of the American Planning Association.

As the title notes, the study is a meta-analysis: a study of 50 other studies about travel and the built environment. The authors look at the results from each of the 50 studies, and then pool all of those results into ten built environment measurements, including intersection density.

Their findings? Of all the built environment measurements, intersection density has the largest effect on walking — more than population density, distance to a store, distance to a transit stop, or jobs within one mile. Intersection density also has large effects on transit use and the amount of driving. The authors comment,

This is surprising, given the emphasis in the qualitative literature on density and diversity, and the relatively limited attention paid to design.

In other words, intersection density is the most important factor for walking and one of the most important factors for increasing transit use and reducing miles driven, but gets relatively little attention in research and in public policy.

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Consider two views about sustainable cities. Call one the Green City, and the other the Compact City.

Green City: A sustainable city is a green city. It has lots of plants and trees that make the city more beautiful, provide habitat for wildlife, and help clean the air and water. It even has community gardens where people grow food and flowers.

Compact City: A sustainable city is a compact city. It has lots of buildings and activities conveniently close together so people can walk, bike, and take transit. It even has paved squares and plazas where people gather and participate in markets, performances, free speech, and recreation.

The Green City is popular as never before. Everyone wants more trees, more landscaping, more living green in their neighborhoods. Stormwater standards are shaping up to be the major vector by which the Green City is delivered — even mandated, in many cases. What does this mean for the Compact City? Is there a conflict between the two views?

In fact, both views are necessary. We have the technical know-how to create neighborhoods that are both compact and green. But sometimes standards and regulations don’t recognize this, particularly stormwater standards. Well-intentioned stormwater standards and regulations can put compact urban development at a disadvantage. They may have the unintended consequence of promoting sprawl, which hurts watersheds more than compact development.

Unlike many barriers to compact development, this is not a technical, social, financial, or even political problem. It is largely an administrative problem. Doing the right thing is simply more difficult for administrators.

This essay suggests four guidelines for stormwater management that support and encourage compact neighborhood development. These guidelines can help put regulations back on the right track, and may also help to make the job of administering stormwater more manageable:

1. Recognize density as a best management practice
2. Allow off-site mitigation, preferably in the neighborhood
3. Plan according to the Transect (neighborhood context)
4. Design according to the Transect (neighborhood context)

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In a September 2009 paper The Market for Smart Growth, market researchers at Robert Charles Lesser & Co. reported strong market demand for housing in new urban communities. In a number of U.S. cities, their consumer surveys found at least one-third of the market prefers new urbanism, transit-oriented development, and urban and suburban infill communities:

Proprietary consumer research conducted by Robert Charles Lesser & Co. LLC (RCLCo) in various U.S. real estate markets has consistently found that about a third of respondents, given the option, would seriously consider New Urbanist communities and housing products in selecting a new home. The majority of the RCLCo studies were conducted for builders and developers as input to planning new smart growth developments. … An examination of the survey evidence relative to consumer housing preferences in the context of demographic projections demonstrates that the size of the market for dense walkable communities is increasing. (emphasis added)

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This summer, members of the Congress for the New Urbanism will vote on LEED for Neighborhood Development. LEED-ND is a system for rating the sustainability of neighborhoods. The vote is a membership referendum on whether CNU endorses the release of LEED-ND in its present state. To encourage informed participation in the vote, the DC chapter of CNU has released An Introduction to LEED-ND for CNU Members.

The six-page article covers the essential points that CNU members should know as they consider their ballot. Topics include the background of LEED, how the system is administered, credits of special interest to new urbanism, what the system does and does not do, and the purpose and meaning of the vote. The article is written by Laurence Aurbach, CNU DC Chapter secretary and member of the LEED Location and Planning Technical Advisory Group.

Cross-posted from CNU DC

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Part One of this essay covers the background, characteristics and drawbacks of functional classification, and evaluates some of the leading alternatives. Part Two continues by proposing a replacement, a sustainable transportation network classification, covering the block-scale and neighborhood-scale relationships. Part Three concludes by covering the city-scale relationship and the congestion-related impacts of a sustainable network.

City Scale

The ideal pattern of regional growth has been debated at least since the 19th century. In the 1960s and 70s the focus of the debate sharpened on efficiency and sustainability, and the “Compact City” was suggested to be the ideal. The Compact City redirects all growth into a single urban core, maximizing density while minimizing the consumption of farms, forests and agricultural land. It explicitly counteracted the dominant trend of decentralized suburban sprawl.

Some of the benefits of the Compact City idea have been confirmed by researchers. Cities with higher density and more compact form have much less per capita driving (Newman and Kenworthy, 1999). In existing cities, the trend of sprawling suburban growth causes an explosion in the amount of auto driving; a policy of refocusing growth, mixed use and transit in the urban core will halt that explosion and slightly reduce the amount of driving (Simmonds and Coombe, 2000).

Analysis of city-scale development patterns shows that focusing growth on high-capacity transit nodes will have the greatest CO2 reduction effect. Image credit: Eliot Allen, “Cool Spots”

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Part One of this essay covers the background, characteristics and drawbacks of functional classification, and evaluates some of the leading alternatives. Part Two continues by proposing a replacement, a sustainable transportation network classification, covering the block-scale and neighborhood-scale relationships. Part Three concludes by covering the city-scale relationship and the congestion-related impacts of a sustainable network.

A sustainable network classification ideally will do several things.

• Actively encourage sustainability (as defined previously in the sustainable transport section); do not support unsustainable network patterns and operations.
• Be concise, easy to remember and easy to explain.
• Address a range of scales, a range that is at least as wide as that covered by functional classification.
• Incorporate advanced knowledge about network function and best practices in network planning.

To reach these goals, a sustainable network classification is proposed. The classification has three primary relationships, each applying to a different scale. The three scales are block scale, neighborhood scale, and city scale. This allows each relationship to focus on the factors most relevant to its scale, without unnecessarily confusing factors from different scales or combining them inappropriately.

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Every field has its foundational working concepts and the field of traffic engineering is no exception. It has a concept called functional classification, which is the core, guiding idea underlying the roadway system of the United States and many other nations. Functional classification is the conceptual foundation of the auto-dependent built environments where most Americans live.

The primary vision of functional classification is moving more and more cars at faster and faster speeds. This has certain benefits, but also a wide range of disastrous consequences for the built environment and the people who live in it. Hundreds, possibly thousands of reform-minded transportation planners and engineers have determined that the roadway functional classification system should be replaced.

It should be replaced by guiding concepts that support a more efficient, safer, less-polluting transportation system – concepts that support a wider range of choices for neighborhood living and daily travel. What factors should be considered when formulating a sustainable transportation system? What proposals have already been made?

Part One of this essay explores those questions. Part Two continues by proposing a replacement, a sustainable transportation network classification, covering the block-scale and neighborhood-scale relationships. Part Three concludes by covering the city-scale relationship and the congestion-related impacts of a sustainable network.

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The Brad Pitt-narrated PBS series e² ( “the Economies of being Environmentally conscious”) has several episodes about urban design and planning. For a general introduction to walkable, transit-oriented design and planning, I recommend the episode “Portland: A Sense of Place.” It focuses on the city’s rail transit and aerial tram, the Pearl District redevelopment, and the quality of life that can result from downtown revitalization with good urban design.

Even better is the episode “Seoul: The Stream of Consciousness” which focuses on Seoul’s Cheonggyecheon Restoration Project. This was a major freeway in the heart of the city that was torn down and replaced with a linear park and recreated running stream. The best thing about this episode is the sense of hope and renewal for the city that is conveyed by the residents’ pride in their new park.

These episodes are beautifully produced, not wonky at all, and will certainly hold anybody’s attention. The episodes can be viewed at www.e2-series.com. Click on “Webcasts” and scroll down to the episode titles. They are also available on DVD and from iTunes.

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The report Life-cycle Environmental Inventory of Passenger Transportation in the United States bills itself as “the first comprehensive environmental life-cycle assessment of automobiles, buses, trains, and aircraft in the United States.” The report, by Mikhail V. Chester of the Institute of Transportation Studies at Berkeley, goes far beyond counting the fuel consumed by vehicles. It considers the energy and materials used to build stations, terminals, roadways, runways, tracks, bridges, tunnels and parking, as well as maintenance, heating, lighting and more. A full life-cycle accounting of travel modes has been a long time coming; it is critically needed and tremendously welcome.

The findings on life-cycle energy use are summarized in this chart:

Read on for a summary of the findings, and a discussion of how the results are affected by urban design context.

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There are a variety of actions that property developers may take to help solve global warming. One is the purchase of carbon offsets — financial credits representing renewable energy or other facilities that reduce greenhouse gas emissions. Developers may purchase carbon offsets to offset the vehicle emissions associated with their land development projects. This is undoubtedly better than no action at all; however, offsets suffer from a number of functional and philosophical shortcomings that render them less-than-optimal as a solution. There are more direct and effective actions available, and those are what the sustainable development industry should encourage.

There have already been flaws uncovered in the carbon offset industry, ranging from obvious cheating and scams, to sincere firms using flawed calculation methods. For the purpose of this discussion, let’s ignore all of that. Let’s assume that all carbon offsets adhere to a high standard like the Gold Standard.

Even so, there is something less than ethical about paying somebody else to solve the problem you aren’t solving yourself. Especially when they happen to be halfway around the world. Whatever happened to “Think Globally, Act Locally”? That saying is drawn from a distinguished philosophical tradition (Leopold Kohr, E.F. Schumacher, Rene Dubos, etc.) and it is still relevant today.

Carbon offsets perpetuate the fiction that we can pay others to solve global warming while doing nothing to change our own patterns of energy use. All energy experts recognize that it will be extremely difficult to replace the current level of energy production with clean, carbon-free sources. Many claim it is impossible. The task of converting to carbon-free energy will be far easier if it is accompanied by a reduction in the demand for energy. Especially here in the U.S., we cannot simply expect technology to fix all of our carbon emissions. We are so profligate in our usage that some degree of demand reduction will be required. Our challenge is to reduce energy demand while maintaining a high quality of life.

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At the CNU Transportation Summit 2008, two presentations were especially consequential for the study of street networks. Both reported preliminary findings about the public safety implications of street connectivity. The results deserve attention from planners and transportation engineers.

Norman Garrick and Wesley Marshall, of the University of Connecticut’s Center for Transportation and Urban Planning, investigated the relationships between connectivity, network configuration, density, severe vehicle crashes, and mode choice. Matt Magnasco of the Charlotte (N.C.) Department of Transportation, studied the effect of connectivity on fire station service area and capital facilities planning.

In the extended entry, summary descriptions of both presentations.

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The winners of the Prix Rotthier pour la Reconstruction de La Ville 2008 have been announced, and they are gems. The Prix Rotthier prizes are given once each three years, and the theme of this year’s competition was “the best urban neighborhood built in Europe in the last 25 years.”

Not only are the winners beautiful and functional, they were judged to have been conceived and designed according to many of the principles of sustainable development and the EU Green Paper for the Urban Environment. These include revitalization of existing cities and suburbs with compact, mixed use development; integrating land use and transportation for more walking, biking, public transit and fewer motor vehicles; harmonious small and medium industry; energy efficiency and green building; waste reduction and recycling; parkland and integrated soil and water management; and not least, to “defend the architectural heritage against the uniform banality of the international style, respecting rather than imitating the old.”

The competition has done a service by providing tearsheets with site plans, photos and statistics on each of the ten winners. However, descriptive material is lacking (until the catalog is published in late 2008), so this post will give capsule descriptions of three neighborhood-scale projects, along with links to more information.

1. Plessis-Robinson, France

Photo credit: City of Plessis-Robinson

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A story about record train ridership in the UK includes this impressive graphic:

Image credit: The Independent

The chart is based on the Association of Train Operating Companies (Atoc) booklet The Billion Passenger Railway. The booklet features several articles — including one that forecasts that the competitiveness of 21st century cities will depend on their high speed rail links. Andrew Curry reports from September 2083:

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For old brick houses, it’s as energy-efficient to renovate — and possibly more so — as it is to tear down and build new. That’s the conclusion of a study by the Empty Homes Agency, a UK nonprofit that works to bring empty homes back into use.

Large homebuilders in the UK claim that new construction is many times more energy efficient than older properties like Victorian houses. That’s true for operating energy, counter the environmentalists, but what about “embodied” energy — the energy it takes to manufacture building materials? Until this study, no one had calculated the relative importance of each. After analyzing three renovated and three new houses, the conclusion was this:

Previous studies and much of the accepted thinking on domestic CO2 emissions have suggested that demolishing existing homes and building new homes to replace them will contribute to an overall reduction in CO2 emissions. This study suggests that this is not so, and that refurbishing existing homes and converting empty property into new homes can yield CO2 reductions by preventing emissions from embodied energy that would arise from new build.

In the extended entry, more quotes from the study “New Tricks With Old Bricks.”

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As editor of the Council Report VII: On Green Architecture and Urbanism, I am pleased to announce that the publication has been printed and is now available for order.

Green building today is well-defined and increasingly popular. However, green urbanism is only starting to coalesce as a defined or systematized approach to the built environment. The Council Report VII features 21 articles on sustainable construction and placemaking by leading practitioners of new urbanist design, planning and education.

As sustainability techniques are adapted from the building scale and applied to the neighborhood and regional scales, a number of critical issues arise. In the rush to go green, we are seeing more instances of misplaced priorities and poorly conceived approaches to scaling up green techniques. That leads to unintended consequences and worsened environmental performance. Therefore, the Council Report VII addresses questions like:

• What are the best principles and techniques now being developed to coordinate sustainability measures and functional urban design? What are the advanced tools now being developed by urban designers to code and build sustainable urbanism?
• How are firms redefining themselves to focus on sustainability as a foundation of their practice?
• What lessons are offered by leading examples of sustainability policies, built projects, and plans? What are effective guidelines for communicating and marketing sustainable communities? What are the definitions of sustainable urbanism, and how do we measure or quantify it?
• What is research telling us about the sustainability of traditional architectural design and construction techniques, and their performance relative to modernist styles?
• How are universities incorporating sustainable urbanism, and what programs and initiatives are now underway?
• What are the philosophical underpinnings of green urbanism and what are the proposed agendas for future research and advocacy?

In the extended entry, a complete table of contents and a summary of each article.

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