Street-network Sprawl in the world

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).

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

  • nodal degree
  • dendricity, the tree-likeness of the street network
  • circuity, the ratio of the distance by road to the straight-line distance of two locations on the street network
  • sinuosity, the curviness of a street

A higher SNDi means less-connected streets – i.e., more sprawl. For the 10262 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:

How has the world's street networks changed over time?

Taking into account the entire (i.e. aggregate) street network in the world as of 2014, the overall level of street-network sprawl is 3.19, which is in the 40th to 60th percentile of disconnectedness.

The street network in the world spans a total of 26585791 kilometers. The period with the greatest volume of street construction was 1976-1990. These roads have an SNDi of 3.36, which is highly disconnected.

Street-network sprawl of new development

The SNDis of street construction for the respective time periods are 2.57, 3.36, 4.12 and 4.13. In each period, new street development in the world steadily grows more disconnected than in the last. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.79 points, but between 1991-2000 and 2001-2014, it rose by just 0.02.

Aggregate global street-network sprawl

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 2.57, 2.89, 3.04 and 3.19. Overall, the SNDi of the aggregate street network has risen: the street network in the world has become more disconnected. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.32 points, but between 1991-2000 and 2001-2014, it rose by just 0.16.

Where are the most and least disconnected...

Cities? As of 2014, the city with the most disconnected street network in the world is Chaman, Afghanistan with an SNDi of 12.25, which is highly disconnected. Conversely, the most connected city is Akbarpur, India with an SNDi of -3.9, which is very well-connected. See trends for these cities: Akbarpur, Chaman

Countries? Considering the street-network in 2014, Gabon leads the world as the country with the most disconnected street-network with an SNDi of 7.6, which is highly disconnected. On the other hand, the most connected country is Uruguay with an SNDi of 0.74, which is relatively well-connected. Click through to find out more about these countries: Uruguay, Gabon

See the state of street-network sprawl in: