WASHINGTON, D.C. – February 15, 2011 – (RealEstateRama) — Existing research on development patterns and transportation provides no causal link between residential land use and greenhouse gas emissions and leaves tremendous uncertainty as to the interplay of these factors, according to a new publication from the National Association of Home Builders (NAHB). The publication, “Climate Change, Density and Development,” provides a fact-based overview of the state of research on the relationship between development, density, transit and the production of greenhouse gases.
“Climate Change, Density and Development,” is available free of charge on the NAHB website at www.nahb.org/climatechange.
The publication examines the debate about the effects of density on transportation behavior and vehicle miles travelled (VMT), and how transportation choices ultimately may affect greenhouse gas (GHG) emissions. It also explores home energy usage, differences in energy usage between building types, and the concept of embodied energy – the amount of energy used in manufacturing, transporting and installing the materials that go into a home.
NAHB asked two highly regarded, impartial research organizations to review the state of knowledge and understanding on these complex issues. Abt Associates, a science and public-policy research firm based in Cambridge, Mass., and ECONorthwest, an economic consulting firm based in Eugene, Ore., conducted extensive reviews of existing research on density, land-use patterns, vehicle usage and GHG emissions and returned two separate reports.
Among the key findings from the research:
* The assumption of a causal connection between density and GHG emissions is based on prevailing beliefs within the planning community and not on verifiable scientific research or analysis.
* After controlling for socioeconomic factors, density does have some influence on vehicle miles traveled (VMT) and transportation choice. However, the weight of the evidence suggests that the effect of density on travel behavior is modest. In fact, doubling density results in only about a five percent decrease in VMTs.
* Density and community design have only a modest impact on transportation choices and travel behavior. They have a greater impact on walking and bicycling.
* The density at the destination – the place of employment – is more important than residential density in shaping commuters’ decisions to use public transit.
* Densely developed cities with centralized employment are the best candidates for fixed rail transit, yet the dispersion of jobs from central cities in recent decades is well-documented.
* The energy and emissions required to manufacture, transport and install materials used in construction (embodied energy and embodied emissions) must also be factored into the equation when considering the long-term efficiency of different development patterns as well as transit facilities.
* The researchers conclude that changes in policies that affect the cost of car ownership, such as increases in gas taxes or the price or availability of parking, are more effective in changing travel behavior than any other policies, if that is the core objective.
The detailed research reports from Abt Associates and ECONorthwest, as well as other analysis of climate change and related issues, can be found at www.nahb.org/climatechange.
“Home builders support smart growth, including higher density development and a variety of transportation options,” said Jerry Howard, NAHB’s Chief Executive Officer. “But we also feel strongly that land use policy should be based on solid evidence and should give equal weight to a community’s many needs, including housing choice and affordability.”
NAHB has long been a leader in green building and smart growth, Howard said, and has adopted policies setting forth its beliefs and priorities in both of these important areas. NAHB’s smart growth principles call for efficient use of land, a comprehensive process for planning growth, fair and balanced funding of infrastructure, revitalization of older suburban and inner city communities, and a wide range of housing choices that meet the needs of families across the economic spectrum.
Howard added that the research makes it clear that care must be taken as policy decisions are made about the future of the nation’s homes and communities. Solutions that seem simple are often complex and fraught with tradeoffs.
“Decision makers also must be mindful of potential unintended consequences as they assess this complex web of issues,” Howard said. “Before we change the shape of our communities, before we change the way we live, we should make sure the changes we make will deliver the desired results.”