Let’s talk about sprawl around metro Detroit! You probably know what it is in a general sense — city growth outside of the denser, older urban core — and what it looks like in our region (looking at you, isolated, cookie-cutter developments in northern Macomb). But it turns out, you can drill down and actually quantify one aspect of sprawl, thanks to the Street Network Disconnectedness Index.

Environmental studies Professor Adam Millard-Ball and economist Christopher Barrington-Leigh came up with a measurement of street-network sprawl that describes how well streets connect, then used it to visualize sprawl for every mapped street across the globe. 

In a nutshell, they found that urban sprawl and disconnectedness is increasing around the globe, with a particular rise in gated communities. You can explore the full map here.

While there aren’t that many new streets and communities under construction around Metro Detroit, the map still lets you visualize how connected and walkable different areas are, or often aren’t.

In the index, streets that are disconnected indicate more sprawl. The factors they looked at are nodal degrees of intersections, or how many streets intersect; dendricity, or whether a network is “tree-like” and therefore has only one route to reach nodes; circuity, or how direct it is to get between nodes (aka cul-de-sacs); and sinuosity, or how straight connections are. Together, they give a sprawl index for countries and smaller geographic areas. 

To get the gist, here is the sprawl index for a few places, with higher numbers indicating more sprawl:

• Michigan: 3.13
• Wayne County: 1.61
• Oakland County: 3.84
• Macomb County: 3.78
• Washtenaw County: 3.39

When you zoom in further, a grid illustrates the areas with streets that have sprawl-like characteristics — so, even though Detroit has well connected streets overall, there are pockets full of cul-de-sacs and dead ends. 

(On the map, purple areas indicate low sprawl and red shows the areas of highest sprawl.)

A lot of Detroit’s hotspots for disconnected streets are around train tracks, industrial sites and other large properties, like cemeteries. Along the Detroit River on the east side, there are some examples of the types of disconnected street design that typically illustrate sprawl, thanks in part to the canals and some gated developments. Those sections on the map show a sprawl index over 8. 

On the map, blue roads are classified as connected, red roads are dead-ends, purple roads are loops and green roads have only one way in.

Not surprisingly, to get to the really sprawly areas, you have to travel (or click around on the map) into the suburbs. Here are a few chunks of Shelby, Bloomfield and Milford Townships where the sprawl index ranges from 11 to 14.6.

By their nature, disconnected streets make for less walkable communities. 

In their paper “A global assessment of street-network sprawl,” Millard-Ball and Barrington-Leigh also note that sprawl is associated with more car travel, energy use and CO2 emissions: the more sprawl, the bigger the environmental footprint. In high-income countries like the U.S., they found that a higher sprawl index was strongly associated with increases in the number of cars owned per household.

In Metro Detroit, public transit is often absent or weak in areas with disconnected streets. In those sections of Bloomfield and Shelby, you’d have to walk about a mile to get to the nearest bus stop for SMART, the suburban transit system.

The sprawl map looks at changes in road construction over the years, which is more applicable for areas around the world with high rates of urban growth. However, the accompanying paper “Global trends towards urban street-network sprawl” found that New York City and Los Angeles, with historically low sprawl indexes, had some of the highest levels of street-network sprawl among 200 international cities when you just look at construction between 2000 and 2013. 

Once you build those disconnected streets, you’re kind of stuck, even if regional population density fluctuates: street routes almost never change, and “may lock in patterns of urban development for a century or more.” The existing streets can also influence development and urban design in neighboring areas in the future. 

In their explainer for the map, Millard-Ball and Barrington-Leigh sum up pretty simply why it’s worth paying attention to street connections in the first place: 

“The street network is permanent, and its connectivity affects the livability and environmental footprint of cities for decades and centuries to come. In places with more connected streets, residents drive less and walk more. Sprawl is associated with worse outcomes for health, the environment, overconsumption, social segregation, and equity.”

Header image: Aerial photo of American suburb. Flickr/La Citta Vita