The Walkability Factor

walkable grid – small block size // less walkable subdivision – large block size

In last week’s Times, Chris Leinberger argued that the apparent shift in homeowner preferences toward walkable, urban neighborhoods will spell decline for the far-flung auto-oriented suburbs.  Leinberger, a Brookings fellow and U-M professor, cites a recent survey finding that only 12% of future homebuyers will continue to want large houses in car-dependent suburbs.  Across the U.S., this shift, caused by changing demographics and homeowner preferences, would raise demand for housing in central cities and the denser suburbs.  Leinberger’s prediction may or may not become reality, but other evidence does suggest a demand for, and undersupply of, walkable, transit-friendly neighborhoods [1, 2].

If Leinberger is correct, what would this mean for metro Detroit? Which places might see increased demand?  This is a complex question and we can’t predict what will happen. But it’s interesting to look at one factor: walkability.  Leinberger suggests that neighborhoods in the most demand will be those that are walkable.

Which places are walkable?

Walkscore gives a quick indication of which neighborhoods are currently walkable.  The score is based on the number of destinations within walking distance; it doesn’t consider things like crime level or pleasantness of a street. Unfortunately, according to Walkscore only a few neighborhoods in metro Detroit receive a high score (e.g., Ferndale, downtown Pontiac).  In most of the region, it’s hard to go anywhere by foot.

Which places have the potential to be walkable?

Maybe some places with a low Walkscore are potentially walkable.  For this quick analysis, we will look at just one ingredient of walkability: street pattern.  Research studies find that street pattern correlates with pedestrian activity [3, 4]. In general, people walk more when streets are closer together, and a grid pattern is more conducive for walking.

Researchers often use block size to measure street pattern. Previous research suggests that a neighborhood is walkable for the average resident when blocks are no larger than 440 x 440 feet, or 4.4 acres [5].  Traditional street grids are usually smaller; in metro Detroit, the street grid produces average blocks of less than 2.7 acres.

 Average block size, one ingredient of walkability.  Blue indicates the most walkable street grid.

The map shows average block sizes in the Detroit region.  Blue indicates a walkable street grid, or something close to it. Yellow indicates streets too far apart to be walkable.  (Because this map is based on Census TIGER files, not street data, it is only an approximate estimate of block size.)

Block size is not all that matters. To be walkable, neighborhoods need destinations (schools, grocery stores, jobs) within walking distance. They need a certain density (usually at least 20-25 dwelling units per acre).  They need to be safe, with good sidewalks, lighting, and protection from traffic.  The above map does not include any of these factors. But the map does indicate, approximately, which areas have the underlying structure for walkability, upon which more convenient destinations and a better walking environment might be built.

[1] Levine, J. and L. Frank. Transportation and land-use preferences and residents’ neighborhood choices: the sufficiency of compact development in the Atlanta region.  Transportation, 2007; Vol. 34, Number 2, 255-274.

[2] Levine, J. and A. Inam.  A Choice-Based Rationale for Land Use and Transportation Alternatives Evidence from Boston and Atlanta.  Journal of Planning Education and Research, 2005; 24(3), p. 317-330.

[3] Saelens, B. and S. Handy. Built Environment Correlates of Walking: A Review.  Med Sci Sports Exerc. 2008 July; 40(7 Suppl): S550–S566.

[4] Saelens, B., J. Sallis, and L. Frank.  Environmental correlates of walking and cycling: Findings from the transportation, urban design, and planning literatures.  Annals of Behavioral Medicine, Volume 25, Number 2, 80-91.

[5] Moudon, A., C. Lee, A. Cheadle, C. Garvin, D. Johnson, T. Schmid, R. Weathers, L. Lin. Operational Definitions of Walkable Neighborhood: Theoretical and Empirical Insights. Journal of Physical Activity and Health, 2006; 3, Sppl 1, S99-S117.