Measuring housing affordability: A test case

Last week, we mentioned the release of a new tool from the Center for Neighborhood Technology that measures the true cost of housing affordability, by also considering the transportation costs of each area. (Note: the Washington Post had a good story about the index here.) A few other outlets have done their own local test to see how prices shake out in their area, notably Erica Barnett with The Stranger in Seattle, where the city comes out much more affordable than the suburbs.

For my test of the tool, I went back to my hometown county in suburban Atlanta — Gwinnett County. Long one of the fastest growing counties in the country, the sprawling county northeast of Atlanta has a reputation for affordability, and certainly did when we moved there in 1990. When my parents chose to locate there, it was partially because of the access to Interstate 85 for my father’s commute into his job in Atlanta — a decision that thousands made over the decades.

By comparison to many of the other 51 cities measured in the index, Atlanta is one of the more affordable metro areas on the whole, and when you simply look at housing cost in Gwinnett, much of the county falls in the area in light yellow — where housing is 30% or less of the median income. (Left) Especially the further east and north that you go in the county. Which follows the pattern of “driving til you qualify.”

But when you add in transportation costs, much of the county turns blue, meaning that housing plus transportation costs in those areas represents 48% or more of the area median income — a sizable chunk to manage. As a result, many of those people looking for the cheaper housing further out end up with a deal that is not so good. (right)

Gwinnett affordability
Left – Gwinnett housing costs. Blue = 30% or more of AMI
Right – Gwinnett housing + transportaton costs. Blue = 48% or more of AMI

More maps after the jump…

The H+T Index also allows you to drill down into the data, by clicking on “advanced” on the left side of the map. Doing so allows you to check out some correlating factors. Look at how many vehicle miles each household travels across the county. (darker colors = higher rates). The rates of VMT seem to correspond loosely to the stripes of affordability in the above right image:

Gwinnett VMT
Gwinnett vehicle miles (VMT) per household

The northern side of Atlanta has been home to the lion’s share of growth for the last 30 years or more, even creeping all the way up towards Tennessee. (The New Yorker featured a few of those “extreme commuters” in this piece, There and Back Again). The tool unfortunately doesn’t measure some of the counties considered part of the metro area northward, but you can see the pattern moving into the land that was countryside when I moved there in 1990:

North Atlanta AffordabilityLeft – N. Atlanta housing costs. Blue = 30% or more of AMI
Right – N. Atlanta housing + transportaton costs. Blue = 48% or more of AMI

Much of the Atlanta region as a whole looks fairly affordable, but add in transportation, and much of it area turns blue. (Note, this has likely gotten worse in the last 8 years, but the Index uses 2000 Census Data.) Interesting to note that the areas inside the perimeter (I-285) don’t change much. In fact, most of the change comes around the edges of the image, not the center.




Atlanta HTIndex
Left – Metro Atlanta housing costs. Blue = 30% or more of AMI
Right – Metro Atlanta housing + transportaton costs. Blue = 48% or more of AMI

And once again, affordability corresponds very loosely to the rates of VMT in the region.

Atlanta VMT
Atlanta VMT per household.

All screen grabs from the Center for Neighborhood Technology’s Housing + Transportation Affordability Index