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Indicator: Walkability Index

Data and Data Discussion provided by Sustainable Seattle

Neighborhood Walkability Index, King County

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Upstream Indicators
  •   Housing Affordability by City --- Homes prices have increased at a greater rate than incomes over the last two decades, making home ownership less affordable. However, rents have increased at a slower rate, generally in line with median household incomes.  (view data graph)
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Downstream Indicators
  •   Housing AND Transportation Costs as a Percentage of Budget --- There is no on-going reporting for this indicator broken down for King County or the Central Puget Sound, though there are multiple data sources showing that the costs of transportation and housing are going up in the region. Recent hikes in gas prices indicate that these costs will continue to escalate.  (view data graph)
  •   Prevalence of Overweight & Obese Adults --- The proportion of King County adults who are overweight and obese continues to climb. In 2006, almost one in five adults were obese and more than half were overweight. Nearly nine percent of school age children were overweight.  (view data graph)
  •   Vehicle Miles Traveled --- In 2007, VMT for the Puget Sound region increased by 0.6 percent over 2006, continuing an almost 30-year trend. Annual VMT has decreased only three times since 1980 when the first estimates became available.  (view data graph)
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Related Goals

Having the goods and services people depend on located within walking distance to their work and homes encourages a healthier street life, which helps to stimulate the local economy and create safer, more livable communities.

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Sustainability Snapshot:

People tend to walk more in mixed-use neighborhoods that are well planned and designed. Different destinations, such as parks and neighborhood gathering places, libraries, community centers, and shops and services, interwoven with pedestrian friendly pathways and streets, encourage people to walk more. Walkable neighborhoods can positively affect other issues such as pollution, health and traffic congestion. The Walkability Index considers residential density, the number of street connections, and the mix of homes, stores, parks, and schools in a neighborhood.

Sustainability Trend:

In 2005, King County finished a major study called “Land Use, Transportation, Air Quality and Health” (which led to the current program HealthScape), that measured how specific land use and transportation actions affect air quality, mobility, congestion, and public health. No trend data are yet available.

Data Discussion

The Indicator Defined

For each King County Census blockgroup, a “walkability” index was derived as a function of net residential density, retail floor area ratio, land use mix, and intersection density.

Data Interpretation/Evaluation

The Walkability Index considers residential density, the number of street connections, and the mix of homes, stores, parks, and schools in a neighborhood. The Walkability Index map (Figure 1) outlines the areas of King County with high, medium and low walkability. The darker shaded areas indicate increased connections among places to live, work, eat, learn, and play.

Creating walkable neighborhoods often depends upon collaboration between numerous government agencies and jurisdictions. Local land use regulations, street plans, and state transportation plans all play a role. For a neighborhood to be truly walkable, it must: (1) have well-maintained sidewalks; (2) have adequate street lighting; (3) provide shelter from the elements at transit stops; (4) control fast-flowing traffic; and (5) be perceived as a low-crime area. Residents must also be aware of the health and environmental benefits of walking. The private sector plays an important role by locating shops and services that provide vitality to an area.

Data Source and Limitations

Data and data discussion is based on the walkability index developed as part of the King County HealthScape project with technical support by Larry Frank and Company.

Methodology: For each King County Census blockgroup, a “walkability” index was derived as a function of net residential density, retail floor area ratio, land use mix, and intersection density. The measures were computed from parcel-based land use data, street centerline files and census data. The fourth variable, retail floor area ratio was introduced to increase the sensitivity to retail use believed to stimulate pedestrian activity.

Each of the four components of the walkability index is described below:

- Net residential density; the ratio of residential units to the land area devoted to residential use per block group.

- Retail floor area ratio; the retail building square footage divided by retail land square footage. The rationale was that a low ratio indicated a retail development likely to have substantial parking, while a high ratio indicated smaller setbacks, and less surface parking; two factors thought to facilitate pedestrian access.

- Intersection density measured the connectivity of the street network, represented by the ratio between the number of true intersections (3 or more legs) to the land area of the block group in acres. A higher density of intersections corresponds with a more direct path between destinations.

- Land use mix, or entropy score, indicated the degree to which a diversity of land use types were present in a block group. For this project, the mix measure considered five land use types: residential, retail (excluding region-serving or “big box” uses of 300,000 square feet or larger), entertainment (including restaurants), office, and institutional (including schools and community institutions).

The four calculated values were normalized for each block group using a Z-score. The walkability index was the sum of the z-scores of the four urban form measures, as stated in the following expression:

Walkability = [(2 x z-intersection density) + (z-net residential density) + (z-retail floor area ratio) + (z-land use mix)]

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Additional Resources

  • Sightline's Map of Walkable King County, WA
    In King County, Washington, compact city and town centers promote walking, while sprawling suburbs discourage it. (The walkability maps and information presented in Cascadia Scorecard 2006 were developed by Dr. Lawrence Frank, Bombardier Chair in Sustainable Transportation at the University of British Columbia, and colleagues Dr. James Sallis of San Diego State University and Dr. Brian Saelens of Cincinnati Children’s Hospital, and were funded by King County, Washington, and the National Institutes for Health.)