I had an idea for an interesting project a few weeks ago while touring Columbia University. The tour group was entering a workshop through a small door. After passing through, I noticed how we had all slowed down to go through and once we spread out, we had not sped up again. I started thinking about how as a crowd, we were acting like a sort of fluid.
This started me thinking about how different situations could be used to model pedestrian traffic flow. If you think of the crowd as a whole acting as a fluid, you can set up interesting experiments. Think about a hallway. It is kind of like a channel for a liquid to flow through. If you cut off half of the flow with a wall you would see some interesting flow patterns appear. People would start getting stuck in front of the wall because they could not squeeze into the flow of people bypassing the wall. People might stop behind the wall in order to get out of the flow. This is similar to fluid dynamics where fluids will form high-flow channels (bypassing the wall) and eddies (slow flow and sometimes backwards flow behind the wall).
Some more interesting behaviors rise when you think about the fact that humans can make predictions and react to more than just a sense of touch. Imagine walking down a hallway in a crowd and seeing a wall blocking half of the hallway ahead. You would naturally try to move to the opposite side of the hallway so that you could easily pass the wall. This would repeat in the minds of everyone who can see the wall. As a group, the crowd would avoid the wall. This is different from how a liquid would interact with a wall because the liquid would not be able to see the wall ahead. So, in order to better match the liquid behavior and the crowd behavior, we can make the wall at hip level. This would prevent people from seeing the wall until they were up close to it and force them into more of a liquid-like behavior.
I am thinking about setting up an experiment at school in the halls related to this (if school ever starts). I think it would be interesting to see how people move around obstacles and to see if that could be matched to certain types of liquids.
Another interesting piece of this is viscosity. Viscosity is the “thickness” of a liquid. It is directly related to the friction between particles. I was thinking about how different human-flow situations would be matched to different viscosities and how this might affect the flow patterns. For example a crowd of business people or students might have less viscosity and might flow better than a crowd of families.
I might look further into this as a way to model traffic flow through buildings using fluids. It could be useful for architects and space planners to quickly test traffic flow. Comment below if you have any ideas about different flow experiments to try out or anything about the viscosity of different types of crowds.