Seattle area looks at how walkable community design can cut global warming

Compact, mixed-use development linked to lowered greenhouse gases.Compact, mixed-use development linked to lowered greenhouse gases.

The world has just a short time in which to act decisively on climate change. King County, Washington, home to Seattle and a number of other population and employment centers in the Puget Sound region, offers a potentially important example of how governments can measure the relationship between land-use patterns and greenhouse gas emissions — and thus improve development across a region.

King County is working to reduce carbon dioxide emissions in the Seattle area and bring future development more in line with smart-growth and new urbanist thinking. The county’s most recent comprehensive plan update calls for greenhouse gases to be slashed by 80 percent from 2007 levels by 2050. Our team has worked on two studies to support these efforts: a countywide census block group map of CO2 emissions from transport that can be used in development review, and the addition of climate change outcomes within a planning model known as I-PLACE3S developed by the Sacramento Council of Governments.  

In applying research to policy, there is a tension between the need to act quickly and the need for more information. The tendency to be cautious and wait for a high degree of certainty may inhibit timely application of information to policy. This is especially true in the case of climate change, when there is a short time frame in which to make dramatic changes. In this case, we should be guided by the precautionary principle found in medicine — make the best decisions possible based on the evidence available, while continuing to gather data.  

Excess vehicular travel
Research that looks specifically at the relationship between land-use patterns and greenhouse gas emissions is in its infancy. Nonetheless, the multiple benefits of walkable community design are beginning to be recognized. The hope is that if we create places that reduce travel distances and encourage walking and mass transit, we can reduce personal vehicle travel, which currently generates approximately 30 percent of US greenhouse gas emissions.

Cutting transportation-related CO2 is one of the most difficult components of global efforts to mitigate climate change. It’s likely that investments that support walkable communities and fast, reliable mass transit will be essential to reduce vehicle demand and greenhouse gases.

Planners have an important role in creating low-carbon communities. California’s passage last year of SB 375 explicitly recognized the role of land use planning in reaching the state’s ambitious climate goals. The recently announced Sustainable Communities Initiative of the US Departments of Transportation and Housing and Urban Development promises to invest in integrated land use, housing, and transportation planning at the regional level.

To achieve effective results, planners and researchers need to collaborate on policy-relevant research, translate their research into practice, and create evidence-based tools that can be used to inform development decisions.

King County’s initiative
The King County Council is deliberating on a proposed ordinance that would require developers to account for, and possibly reduce, carbon dioxide from transportation, building materials, and future energy use. To support the proposed King County regulation, our team predicted and mapped the mean carbon dioxide emissions generated by household travel at the census block group scale (a neighborhood scale area of about 1,000-2,000 households) across the county. We began by analyzing relationships between urban form, demographics, and CO2 emissions from transportation, for 3,000 King County households in the Puget Sound Regional Council’s 2006 travel survey.

This allowed us to calculate mean CO2 emissions for each census block group used by the US Census Bureau. The resulting map (see above) provides a baseline that can be used in the county’s development review process. When a development is submitted to the county, it can be checked to see how its emissions compare to the baseline or average level of emissions countywide. The county can then determine what mitigation is needed.

Scenario planning tools
Planners need tools that can evaluate and compare the potential CO2 effects of rezoning, comprehensive plans, transit investment, and transit-oriented development. In King County we looked at the relationships between urban form, air quality, transportation, and health. We integrated the research results into I-PLACE3S, a Web-based scenario planning tool developed by the Sacramento Area Council of Governments (SACOG). Tools like I-PLACE3S, which provide real-time feedback about the implications of planning decisions, offer an important opportunity to educate stakeholders about the implications of growth and development.

In collaboration with SACOG, we created two new “modules” for I-PLACE3S: a Health module and a Climate/Air Pollution module. These new modules measure urban form at the parcel level, and can incorporate detailed information on an area’s demographics (such as income, age, and employment status).

In I-PLACE3S, planners can now change transit service levels to test the combined, and potentially synergistic, impact of transit investment and urban form changes.  Because King County is a transit service provider, the evaluation of transit service is a key feature.
The new version of I-PLACE3S can be used in a number of planning contexts, including comprehensive planning, transit-oriented development, zoning, and transit investments/service changes, as well as Health Impact Assessment (HIA).

Since the revised version of I-PLACE3S allows planners to test the interaction between transit service levels and land-use changes; it can help to inform and improve transit-oriented-development planning. I-PLACE3S can also be a key tool for assessing the potential climate, air pollution and public health impacts of King County’s comprehensive plan.

Lawrence Frank is the Bombardier Chairholder in Sustainable Transportation at the University of British Columbia, Senior Non-Resident Fellow of the Brookings Institution, and President of Lawrence Frank and Company. Sarah Kavage is a Seattle-based artist and special projects manager at Lawrence Frank and Company.  She holds a masters in urban design and planning from the University of Washington.