Graph below from Michael Southworth, which shows the devolution of intersections over the decades, particularly in the United States.
Intersection Density (Design)
- Meaning:
Intersection density measures how many street intersections exist within a given area — typically the number of intersections per square mile. - Purpose:
It reflects how connected the street network is. Areas with more intersections (especially 3- or 4-way intersections) give pedestrians more route choices and shorter travel distances to reach destinations. - Interpretation:
- High intersection density: Grid-like street patterns, easy pedestrian navigation, shorter blocks (e.g., downtowns, traditional neighborhoods).
- Low intersection density: Cul-de-sacs, disconnected streets, car-oriented layouts (e.g., suburban developments).
- Why it matters:
Greater intersection density typically means better walkability, as it encourages walking, biking, and transit use by improving connectivity and safety through slower traffic speeds.
High Intersection Density
Downtown Chicago: Chicago’s downtown has extremely tight block spacing (some major streets half-block apart) which likely corresponds to very high intersection density.
Downtown / Central Neighborhoods in Older Cities: Many block groups in very dense, gridded “city-center” neighborhoods (e.g., parts of Manhattan, Washington DC, Boston) will score very high in intersection density. The NWI map itself shows highest walkability block groups clustering in dense urban cores.
The Chicago Loop has a Intersection Density score of 19 out of 20. City blocks are usually no more than 500 ft.
The North End of Boston illustrated above has a Intersection Density of 20 out of 20
Medium Intersection Density
Historic Town Centers / Suburban Town Centers: In the NWI methodology guide, they use an example: a “city center / suburban town center” block group that scores relatively high on intersection density.
Older Suburban Neighborhoods: Suburbs with moderate grid / street connectivity — not as tight as downtown but more connected than sprawling suburbs — would likely fall into medium quantiles of intersection density.
Low Intersection Density
Rural or Semi-Rural Block Groups: Very low walkability block groups in the NWI (scores ~1–5.75) often correspond to low intersection density, because they’re more sprawling and have fewer intersections per area.
Suburban / Exurban Development: Areas with hierarchical street networks, cul-de-sacs, and fewer cross-streets (tree-like street networks) will have low intersection densities. This is common in more car-oriented suburbs.
References
Southworth, M. (2005). Designing the Walkable City. Journal of Urban Planning and Development, 131 (4), 246–257. https://doi.org/10.1061/(ASCE)0733-9488(2005)131:4(246)