Most Public Transit Systems Are Too Big for Humans to Comprehend

A group of mathematicians and physicists tried to quantify just how impossible it is to navigate big cities.

If you've ever been to a large city, you've likely found yourself clinging to transportation apps to get around, or staring in confusion at the colorful, labyrinthian subway maps while attempting to plot your route across town.

New research from University of Oxford shows that the disorientation isn't just in your head: Navigating public transportation is really hard. So hard, in fact, it may pass the threshold of what human beings can comprehend.

In the study, published Friday in the journal Science Advances, a team of physicists and mathematicians analyzed transportation networks in 15 major metropolitan cities, including New York, Tokyo, Paris, and London, and found navigating these transit maps often exceeds human cognitive ability.

The researchers found humans can process a maximum of 8 bits (binary digits) of information when planning a trip. We can easily handle information for four objects in our visual working memory: In this case, two key locations (starting and ending point) and two connections in between. Analyzing journeys with two connections and four stations total, the researchers found that 80 percent of trips in major cities like New York, Paris, and Tokyo exceed the 8-bit limit.

Similar to the Dunbar number, a term coined by anthropologist Robin Dunbar that refers to the maximum size of IRL social networks humans can handle, maps should not have more than 250 visible connection points to be easily readable, researchers suggested. The majority of trips on the major urban transport systems studied in the paper exceeded that. The researched analyzed public transit systems in New York City, Paris, Tokyo, Barcelona, Madrid, Seoul, Beijing, Hong Kong, Mexico City, Osaka, Shanghai, Berlin, London, and Moscow.

The problem is that these transit systems simply have too many interconnections.

Mason Porter, professor of nonlinear and complex systems in the Mathematical Institute at the University of Oxford, told Motherboard in an email that planning these trips often becomes more complex than just getting from point A to point B: We have to juggle factors like which route is faster versus which is more simple (fewer connections). When you add other transportation modes like buses and trams, the decision quickly becomes very complex for the human mind.

Porter said map redesigns and experiments on how we learn to navigate cities could help with the information overload. "The traditional view of navigation in cities has to be revised substantially," researchers wrote.

"For cognitive limits, a resident is somebody who has a lot of practice, and that's rather different from somebody visiting a city for the first time," Porter told me. "Animals can learn how to become better at navigating a maze, so we should also expect to be able to measure—with appropriate experiments—people becoming better at navigating in a transportation system."

Of course, if you plug an address into Google Maps, a computer can do all of this for you. But when you are in a new city, perhaps underground without access to directions, it's not necessarily a replacement for having a good map that is actually readable.

The number of megacities with population of more than 10 million has tripled since 1990, and while navigation apps help, the maps themselves may need to be redesigned as cities continue to grow and transportation networks expand.