Street-network Sprawl in United States

What is Street-network sprawl?

Street-network Sprawl is a way to measure urban sprawl, worldwide, through the connectedness of the streets. Less sprawl means more connected, more walkable streets. Well-connected streets – like New York City’s grid – are more walkable and can be served by public transit.

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. A well-connected street network is associated with better outcomes for health, the environment, sustainable consumption, social integration, and equity.

We can quantify how connected street networks are with the Street Network Disconnectedness Index (SNDi).

SNDi -- our measure of street-network sprawl (disconnectedness)

The SNDi is a comprehensive measurement of “sprawl”. It captures:

A higher SNDi means less-connected streets – i.e., more sprawl. For the 10137 cities in our dataset, the average SNDi is 2.25, with half of the cities' SNDis falling between 1.08 and 3.25.

More information on the sprawl index can be found in these research papers:

To see the state of street-network sprawl across the globe, visit the sprawlmap.

United States

What exactly constitutes the spatial extent of the city? For these aggregations, we used the Global Human Settlement Layer Urban Center Database (GHS-UCDB) to define the boundaries of the city. These cities -- or urban centers -- cover areas that are densely populated and built-up, and so may extend beyond the spatial borders of these cities that we may be familiar with. The GHS area is shaded in blue.

View United States on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in United States as of 2014, the overall level of street-network sprawl is 4.02, which is highly disconnected.

Trends in street network construction: The SNDis of street construction for the respective time periods are 2.98, 4.64, 6.09 and 5.88. Street construction in United States increased in disconnectivity initially but has since improved. The streets constructed in 1991-2000 were the most disconnected.

Quantity of street network construction: The street network in United States spans a total of 4521692 kilometers. It is dominated by roads constructed prior to 1975. These roads have an SNDi of 2.98, which is in the 40th to 60th percentile of disconnectedness.

Effect on the aggregate network: New construction in each period adds to the total stock of streets, but does not change streets that have already been built. Therefore, it has a limited effect on the street network as a whole. The SNDis of the aggregate street network in the respective time periods are 2.98, 3.53, 3.8 and 4.02. Overall, the SNDi of the aggregate street network has risen: the street network in United States has become more disconnected. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.55 points, but between 1991-2000 and 2001-2014, it rose by just 0.21.

The level of street-network sprawl in new development in United States peaked in 1991-2000. To get a sense of how street development has changed in United States, we can consider three of its most populous regions: California, New York and Texas. Out of the three regions, Texas does not follow the same trend as the country. The level of street-network sprawl in new development in Texas rose steadily.

How do development practices in United States fare in comparison to others in the world? Most recently in 2001-2014, street construction in United States was the 36th-most disconnected out of the 155 countries in the world. Its position in the ranks since 1975 has risen; relative to other countries in the world, street construction in United States has become more disconnected. United States ranked 67th in 1975, 36th in 1976-1990, 21st in 1991-2000 and 36th in 2001-2014.

The largest city in United States is New York, with a population of 15950700 people. Taking into account the entire (i.e. aggregate) street network in New York as of 2014, the overall level of street-network sprawl is 2.47, which is in the 40th to 60th percentile of disconnectedness. The level of street-network sprawl in new development in New York peaked in 1991-2000.

As of 2014, the city with the most disconnected street network in United States is Roswell with an SNDi of 8.19, which is highly disconnected. Conversely, the most connected city is San Angelo with an SNDi of 0.49, which is relatively well-connected. See trends for these cities: San Angelo, Roswell

The level of street-network sprawl in the aggregate network in United States rose steadily. To get a sense of how the aggregate street network has changed in United States, we can consider three of its most populous regions: California, New York and Texas. Disconnectivity in the most populous cities in United States follow the same country trend.

To date, United States is the 50th-most disconnected out of the 155 countries in the world. Its position in the ranks since 1975 has risen; relative to other countries in the world, the street network in United States has become more disconnected. United States ranked 67th in 1975, 57th in 1976-1990, 55th in 1991-2000 and 50th in 2001-2014.

The largest city in United States is New York, with a population of 15950700 people. Taking into account the entire (i.e. aggregate) street network in New York as of 2014, the overall level of street-network sprawl is 2.47, which is in the 40th to 60th percentile of disconnectedness. The level of street-network sprawl in the aggregate network in New York rose steadily.