How we measure street-network sprawl
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 4 dimensions of SNDi
- Nodal degree: the number of streets meeting at each intersection
- Dendricity: the tree-likeness of the network (dead ends and cul-de-sacs)
- Circuity: the ratio of road distance to straight-line distance between two points
- Sinuosity: the curviness of individual streets
A higher SNDi means less-connected streets – i.e., more sprawl.
A higher SNDi means less-connected streets – i.e., more sprawl. For the 11386 cities in our dataset, the average SNDi is 3.43, with half of the cities’ SNDis falling between 2.31 and 4.13.
More information on the sprawl index can be found in these research papers: