Using a 'virtual slime mold' to design a subway network less prone to disruption

Researchers use ‘virtual slime mould’ to design a TTC subway network less prone to disruption
At left, a map of Toronto showing 17 of the TTC’s 75 subway stations. At right, a network connecting the same 17 transit nodes that was created by a computer model of Physarum polycephalum, otherwise known as a slime mould. Credit: Raphael Kay

It doesn't have a brain and can survive on rotting vegetable matter, but it could offer valuable insights into city planning, according to a team of University of Toronto researchers.

A single-celled amoeboid organism that grows as a greenish-yellow system of veins is called Physarum polycephalum. The veins form a tubular network that is designed to transfer nutrition efficiently.

After they mold broadly over an area, they refine their tubular network to maximize transport of the nutrients. The efficient organic structure of the slime mold could be used to model other networks, including those designed to move people and goods around a city.

Raphael Kay, who joined U of T's Faculty of Applied Science and Engineering as a master's candidate, says that humans aren't the only ones dealing with the challenge of designing efficient, resilient networks.

Lessons from past human architecture were taught to us in architecture school. The slime mold has been shaped by hundreds of millions of years of evolution, so they are more experienced at solving architectural problems than we are.

Kay is supervised by an associate professor in the department of materials science and engineering. A group of researchers from Japan and the U.K. fed a mold of a subway system in Tokyo. The emergence of biologically inspired adaptive network design is a result of the network being strikingly similar to the real thing. Similar studies have been conducted in the context of their own rail or road transportation networks.

Kay and Anthony Mattacchione created a computer model that mimicked the way slime molds build their network. They compared the model's results to those of a real mold grown on a plate, which they fed with oatmeal.

Scientific Reports published the results of their work this week.

Three key metrics were used to evaluate the networks created by the model.

  • Cost, a function of the overall length of all segments
  • Mean travel time, the average length between any two points
  • Vulnerability, the average increase in travel time caused by the removal of a segment

The team saw a correlation between the model and the living organisms, with the deviation between the model and the living organisms less than 4%.

The way in which it was specifically aimed at architects, city planners and other professionals who might be interested in incorporating lessons from nature into their design process is what sets this model apart. The user can specify a maximum cost or minimum travel time and then choose a network that will meet their needs. The model for the graduate architecture course was created by Kay and Mattacchione.

The team created two sample networks from real-world situations to test the virtual slime mold model. One set of points was derived from the locations of various roller coasters and food stands. The other was based on the subway stations in Toronto.

In the Canada's Wonderland example, our model generated a network that would provide a travel time 10 percent faster than the real-life network and 80 percent more resilient in the event that one of the segments gets blocked.

The most striking finding was that the subway network was 40 percent less susceptible to disruption if it had the same travel time as the real thing.

The results may not be that surprising to those who have used these real-life networks, which were not designed with resilience in mind. Kay and Hatton say they are not advocating for these networks to be re-designed from scratch, but rather using them as examples of where their model could offer insights on the best places to add segments, as well as to inform future designs.

Kay says that the model can generate the attractor nodes itself, without the need for designer input.

The team is considering making the model open-sourced to anyone who wants to use it.

It has the potential to bring together expertise and insights from disciplines that have been thought of as separate. They are trying to maximize networks in the same way as the slime mold.

More information: Raphael Kay et al, Stepwise slime mould growth as a template for urban design, Scientific Reports (2022). DOI: 10.1038/s41598-022-05439-w Journal information: Scientific Reports Citation: Using a 'virtual slime mold' to design a subway network less prone to disruption (2022, January 27) retrieved 27 January 2022 from This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.