Suburbs vs. the City

In commenting on a recent editorial, I tried to highlight what I think is a serious blind spot in popular notions of urban planning and sustainability.  In Portland, much thought and effort is directed at "livability."  Few of those efforts though are targeted at families, and in fact measures such as the composting program seem intended to push families out.  I wanted to put some numbers on migration, so I looked at the 2009 ACS data.  I compared figures for the city of Portland to the Portland-Vancouver-Beaverton MSA minus the city of Portland, taking the latter group as an approximation for suburbs.

The data tells an interesting story.  Series 1101 gives total households, families, and families with children under 18 split into three subsets:  Families with children under 6, families with children both under and over 6, and families with all children 6 or older.
At the outset there is an obvious difference in the number of households reported as "families", unsurprisingly singles tend to be attracted to the city.  And at first glance there isn't much difference between city and suburbs when it comes to how many families have kids, 46% vs 49%.  The net result is that suburban households are significantly more likely to have children, one third vs less then a quarter in the city.

Things get weird when you get into the age groups.  The percentage of households with young children is very close, only half a point separates city and suburb.  The difference is concentrated in families with older children:
Now some might construe this as evidence of a shift in preference, that newer parents are more comfortable raising kids in the city and its only a matter of time before the figures for households with older kids come into line. So I looked at 2005 ACS data:

This pattern isn't new.  What it speaks to is a transition, that as children age families are more likely to pack up and move out of the city.  How many people are we talking about?  If Portland had the same share of families with older kids as it has of families with younger kids it would mean an extra 13,355 families.  Averaging that over 18 years and it comes out to 742 families per year.  That's 742 families who tried living in the city, put up with it for at least 6 years and then decided to do something else and embraced suburban car culture.  Each year.  That was the status quo.

Now think about the composting program and how the city gave the functional equivalent of a raised middle finger when people asked what they were supposed to do with diapers.  How many more families will boogie off to the burbs?  The city has a grace period because families are trapped by the rotten housing market but that won't last forever.  Eventually families will regain a choice in housing, and no one should be surprised when they act on it. 

How sustainable is a vision of the city that drives families out into the suburbs?