Income Mixing and Inequality in the Research Triangle

The greater Triangle area—including the cities of Raleigh and Durham—is one of the fastest-growing metros in the county.  Raleigh’s population increased 48% between 2000 and 2012, making it the fastest-growing city in the U.S. over that time.  Affordable housing pressures have come with such strong population growth, and affordability was recently a campaign issue in both Raleigh and Chapel Hill.  As the Triangle continues to grow, policy-makers, planners, and developers must work to ensure that its neighborhoods remain economically and socially integrated.


Click on the map to interact with it.

In this post, we’ve mapped two measures:  the Simpson Index (which measures income mixing) and the 100/25 ratio (which measures income inequality).  Higher Simpson scores (in green) indicate greater intermixing, while lower mixing is in red (the highest possible score is 0.80).  Higher 100/25 ratios (in blue) mean that a neighborhood has many more wealthy households than poor ones; lower values (in red) mean the opposite: more low-income households than wealthy ones.  Neighborhoods with values around 1 have an even distribution of wealthy and low-income families.

Affordable housing pressures in Wake and Durham County

Probably the most notable features on the map are the two low-intermixing clusters in Wake County.  One cluster, located north of Raleigh, extends between Interstate 540 and US-98 along Creedmor Road.  The other, found west-southwest of Raleigh, extends between Morrisville, Apex, Cary, and Holly Springs.  Clicking on the map shows that these neighborhoods are primarily upper-income:  in some neighborhoods between Cary and Morrisville, over 70% of families earn more than $100,000 per year.

Another low-intermixing cluster is found just east of downtown Durham.  Unlike the clusters in Wake County, many residents of these neighborhoods are very low-income; over 70% of households in some tracts earn less than $25,000 per year.  Despite some very early gentrification in the area, these neighborhoods have very few middle-class residents.

Switching to the 100/25 ratio measure of income inequality, the two large Wake County clusters again stand out—this time for having many more wealthy households than low-income ones.  The Durham, in contrast, has many more low-income households than wealthy families.

Outlying counties: concentrated poverty and relative mixing

In the counties outside of Wake and Durham, a pattern emerges:  areas of low income mixing in the (relatively) larger cities and towns surrounded by high mixing.  With the exception of Chapel Hill, these cities are characterized by concentrated poverty; examples include Roxboro, Henderson, Sanford, and Siler City.

The 100/25 ratio shows that nearly all neighborhoods in outlying counties have more lower-income households than wealthy ones.  Upon closer inspection, the discrepancy between the Simpson index (showing higher income mixing) and the 100/25 ratio (showing many more poor households) is largely due to the lack of wealthy households in the outlying counties, and not because of to the preponderance of very poor families.

Creating a more integrated Raleigh-Durham

Unlike many cities, the Triangle has relatively few areas of concentrated disadvantage.  However, the maps show that cities can do more – especially the suburban communities of Morrisville, Apex, and Cary—to expand affordable housing beyond the larger cities of Raleigh and Durham.  These efforts are especially important as these communities have high-quality schools and are close to the growing jobs base of Research Triangle Park.

The findings also suggest the need for neighborhood revitalization strategies for both Durham and many of the towns in the outlying counties, including Louisburg, Siler City, and Henderson.  While many Durham residents fear that such efforts will displace low-income families, policies that protect existing residents can mitigate the downsides of gentrification.

In the map above, we’ve mapped the Simpson Index and 100/25 ratio (once you click to the host site, you can use the arrows to switch between maps).  Click on the i to see information about each measure and the map legend, and you can select on any neighborhood to see the data behind these calculations.  We’ve also included two commonly-used measures of well-being:  poverty rates and median household incomes.

2 thoughts on “Income Mixing and Inequality in the Research Triangle

  1. Pingback: Charlotte Income Inequality | Urban 2 Point 0

  2. Pingback: Transportation Affordability in North Carolina’s Cities | Urban 2 Point 0

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