Procedural design of urban transportation systems

Written by David Omar

The information sharing trait of the homo sapiens is what allowed it to spread exponentially all over the world. Cultural and intellectual growth and evolution is way faster than biological evolution.

One of the most relevant places that this information exchange happens, is at shared spaces within cities.

It’s no surprise, then, that when the first cities started to appear, they all shared some things: they’ve been about shared space, human interaction and encounter, and the exchange of goods and services1.

When a city is just born, all points are not further apart of each other than walking distance. But when a city settlement starts to stretch, transportation systems have to appear2.

And once transportition systems appear, the city settlement starts to evolve.


Urban form and structure

There are some aspects that rule the design of urban transportation: urban form and urban structure.3

The form is the nature or density of development.2 The spatial imprint of a city. Is what confers spatial arrangement and an aparent structure.3

The structure is the set of relationships that arise from the urban form and its underlying interactions of people, freight, and information.3

To grasp the urban form, you look at the city. To grasp the urban structure, you look at its behavior.

Both form and structure are articulated by two fundamental elements: nodes and linkages.3


Here is where the most of urban activities take place (mostly economic, such as production, management, retailing, and distribution).3

Nodes are, ideally, the most accessible places to transport systems.

Nodes emerge thanks to the agglomeration of activities, and at the same time, they nurture those same activities by its own accessibility.


They support the flow between nodes3 and inside nodes, if nodes are big enough.

There is a hieararchy of linkages: from sidewalks, to air and maritime transport systems.

Coevolution of transportation and urban form

We have stated that urban form influences the set of transport systems, and transport systems start to influence urban form.

Radical changes in any transport system, will lead to radical changes in urban form.3

The main effect of transport on urban form is the emergence of new activity clusters3.

The emergence of activity clusters

Metropolitan subcenters

Often called satellites, and more often, suburbs. This new activity clusters are the representation of descentralization4.

There are two of these: satellites and suburbs.

Satellite Suburb
Consumes labor Consumes products
Supplies products Supplies labor
Usually larger in size Usually larger in number

A suburb is a relatively small and structured community. It is adjacent to, and depended upon a large central city.

The two defining characteristics that provide the suburban status are:

  • Ecological position
    • Further than urban neighborhood. Closer than rural neighborhood.
    • Remain dependent of central city as source of goods and services.
  • Commuting
    • Are adjacent to urban centers, but provide jobs for their own and close residents.

When a city is just born, it’ll, most of the times, have one small city center in which all economic activities take place.

As the city grows, various activities start to take place outside the core. That’s the first threshold. The one that marks the appearance of roads, as some communication between periphery and center is needed.

Once a road appear between suburb S[0] and city center C, the commuting time decreases, allowing more people to live in S[0].

When enough people lives in S[0], economic activities start to appear around.

If you repeat the proccess to suburbs S[1], S[2]S[n] you start to have multiple activity clusters other than the city center. Activity clusters that need connections between them.

And that necessity can only be satisfied with the building of secondary roads.


Central Business Districts


  1. McLaren, D., & Agyeman, J. (2017). Sharing cities: A case for truly smart and sustainable cities. Cambridge: MIT Press. 

  2. Troy, P. N. (2004). The structure and form of the Australian city: Prospects for improved urban planning. Brisbane: Urban Policy Program, Griffith University.  2

  3. Rodrigue, J., Comtois, C., & Slack, B. (2013). The geography of transport systems. New York: Routledge.  2 3 4 5 6 7 8

  4. Reissman, L. (1964). The urban process: Cities in industrial societies. New York: Free Press of Glencoe.