Street-network Sprawl in Tehran, Iran

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.

Tehran: region in Iran

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 Tehran, Iran on the sprawlmap

Most recent snapshot: Taking into account the entire (i.e. aggregate) street network in Tehran as of 2014, the overall level of street-network sprawl is 3.01, which is in the 40th to 60th percentile of disconnectedness.

Trends in street network construction: The SNDis of street construction for the respective time periods are 2.72, 2.9, 4.81 and 4.95. In each period, new street development in Tehran steadily grows more disconnected than in the last. This increase has slowed: between 1975 and 1976-1990, SNDi rose by 0.18 points, but between 1991-2000 and 2001-2014, it rose by just 0.14.

Quantity of street network construction: The street network in Tehran spans a total of 20717 kilometers. It is dominated by roads constructed in 1976-1990. These roads have an SNDi of 2.9, 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 2.72, 2.82, 2.91 and 3.01. Overall, the SNDi of the aggregate street network has risen: the street network in Tehran has become more disconnected.

The level of street-network sprawl in new development in Tehran rose steadily. To get a sense of how street development has changed in Tehran, we can consider three of its most populous cities: Tehran, Pardis and Qarchak. None of the most populous cities follow the same trend as the region. The level of street-network sprawl in new development in Tehran peaked in 1991-2000. The level of street-network sprawl in new development in Pardis followed a zig-zag trend. The level of street-network sprawl in new development in Qarchak followed a zig-zag trend with an overall increase.

How do development practices in Tehran fare in comparison to others in Iran? Most recently in 2001-2014, street construction in Tehran was the 6th-most disconnected out of the 31 regions in Iran. Its position in the ranks since 1975 has risen; relative to other regions in Iran, street construction in Tehran has become more disconnected. Tehran ranked 26th in 1975, 10th in 1976-1990, 3rd in 1991-2000 and 6th in 2001-2014.

As of 2014, the city with the most disconnected street network in Tehran is Pardis with an SNDi of 5.14, which is highly disconnected. Conversely, the most connected city is Sharifabad with an SNDi of 1.05, which is relatively well-connected. See trends for these cities: Sharifabad, Pardis

The level of street-network sprawl in the aggregate network in Tehran rose steadily. To get a sense of how the aggregate street network has changed in Tehran, we can consider three of its most populous cities: Tehran, Pardis and Qarchak. Out of the three cities, Pardis and Qarchak do not follow the same trend as the region. The level of street-network sprawl in the aggregate network in Pardis followed a zig-zag trend. The level of street-network sprawl in the aggregate network in Qarchak was at its lowest in 1976-1990.

To date, Tehran is the 19th-most disconnected out of the 31 regions in Iran. Its position in the ranks since 1975 has risen; relative to other regions in Iran, the street network in Tehran has become more disconnected. Tehran ranked 26th in 1975, 16th in 1976-1990, 16th in 1991-2000 and 19th in 2001-2014.