June 8, 2016

Reimagining suburbia for multimodal transportation

Elyse O’Callaghan

Evidence for the ballyhooed urbanization trend in the US generally relies upon data at the metropolitan level, and tends to obscure the fact that most of this growth is occurring in suburban-type areas rather than in dense urban cores.

Commuting in America, Fig. 4-10

However, this trend is more nuanced than a simple binary urban vs. suburban split can properly capture. This is an important distinction because a proper recognition of consumer desires could allow for intelligent suburban development that allows for and encourages multi-modal transportation splits rather than the present, cul-de-sac manifestation of suburbia that makes the car king and inevitably leads to greater energy consumption, higher emissions, and severe roadway congestion.

First, to recognize popular trends in neighborhood types, it is important to consider population densities and other characteristics that define an area as urban or suburban rather than simply relying on political boundaries. Jed Kolko, the chief economist for Trulia – an online real estate company – performed an analysis of occupied postal code data from the US Postal Service monthly reports along with household type and density values from the US Census Bureau at the ZIP code level to determine more granular urban and suburban growth trends in the US between 2011 and 2014 [1]. Based on these household measures and other “measures of urbanness” such as diversity metrics and utility of non-motorized modes, a spectrum of urban/suburban deciles were developed and household growth was plotted as shown in Figure 1.

As this shows, while the greatest growth occurred in the most suburban neighborhoods, the most urban settings saw ~3.2% growth, which is on par with the 7^th and 8^th decile of suburban-style neighborhoods. Beyond that, urban-style neighborhood growth remained consistently near 2%.

Concerning what drives these different trends, age appears to be a primary factor. According to another study by Kolko, trends in urban living decline for individuals past their mid- to late-twenties as shown in Figure 2. To demonstrate this shift with a visual that demonstrates this shift in a starker manner, Figure 3 comes from a newgeography post that looks at how US cities have been abandoned by members of Generation X.

The author of the newgeography post makes an excellent point in noting that:

“Rather than place all their bets on attracting 20-somethings, cities must focus on why early middle-age couples are leaving. Some good candidates include weak job creation, poor schools, high taxes and suffocating regulatory environments. Addressing these issues won’t keep all young adults in urban settings, but it might improve the chances of keeping a larger number.”

Further, desire for walkability within a surrounding neighborhood has been established as a desirable feature within the housing market as shown in Figure 4 and further highlighted by the fact that walkscores are highlighted by online real estate sites as a positive household attribute.

Taken together, these trends and stated preferences have a few implications from a planning perspective; first, it suggests that individuals are open to and pursuing the idea of dense, urban living, however the realities of this lifestyle are perceived as too daunting after a certain age and seemingly once children enter the equation. Based on this, efforts to zone and develop land in a way that is perceived as more suburban but provides the relative mixed-use development and access to support transit service ridership requirements is critical. A great example of this is the Urban Villages Strategy (UVS) in Seattle. Unlike the rest of the country, where 36 of the 50 regions experiencing the most growth have seen the majority of growth outside of the central city, the opposite has been true for Seattle as shown in Figure 5. The fact that 79% of housing and 78% of job growth occurred in City of Seattle UVs per the 1994 UVS, indicates that managed and active urban planning can impact housing choices.

As shown in Mark Hallenbeck’s “famous green slide” that holds density constant on the top and bottom of the figure (Figure 6), land-use planning and develop are critical factors when considering a neighborhood’s ability to sustain alternative transportation modes.

Essentially, even if people continue to move to the suburban-style neighborhoods of metropolitan areas, with better planning and implementation of mixed-use developments, suburbia can be re-imagined from the cul-de-sac connected to a congested arterial of the past to a cozy neighborhood that is walkable and better suited to multi-modal transportation in general.