Specifically, the type of simulation modeling I was looking at in my thesis was “agent-based behavioral simulation modeling”, which is just a fancy, academic version of playing The Sims all day. In agent-based simulation modeling, you set up an environment (a street corner, a subway station, a mall), populate them with a bunch of “agents” (people and/or cars) with specific personalities and behaviors, as well as destinations they want to get to, and then run the simulation to see how they all interact with each other within the space on the way to each of their destinations. The simulation is “agent-based” because the behavior of each individual agent is generated first (how fast they move, how close they will get to another individual before they slow down, how much they want to avoid or not avoid other individuals, for example), and the simulation is based on how all the agents — each with their individual behaviors and responses and goals — interact with each other when placed in an environment. So basically, The Sims.
I say this all to introduce the idea of the phantom traffic jam, which is the phenomenon of when a slowdown on a highway occurs for seemingly no apparent reason. You are driving normally, and then the cars up ahead all slow down and jam up, and then when you make it out of the jam, the cars all speed up and space out again. There was no accident, no on-ramps or off-ramps, no lane closures, nothing. So if the highway was clear, what caused the jam?
The answer is (the way I am able to understand it) based in this idea of each car acting as an individual agent. Each driver in each car has certain behavioral attributes: each has an average driving speed, each has a variation of how much they speed up and slow down to try to maintain their average speed, each has a certain delay in braking response when they see the car up ahead of them brakes. And each driver has a certain threshold of distance on how close they need to be to the car ahead of them before the slow down or slam on their breaks.
The best way to visualize how a phantom traffic jam forms is if you imagine a bunch of cars driving in a loop, all spaced out equally but a little too close to each other to drive completely freely. If these cars were driven by perfect drivers, they would all maintain the exact same speed and would all stay the exact same distance apart from each other and would would drive in a loop perfectly without any issue.
But people are not able to be this precise (and please please do not read this essay as an argument for self-driving cars… you will have to go to another writer somewhere else for that opinion). When people drive, they speed up slightly and slow down slightly, they don’t drive along a perfect path — and these little… I hesitate to say “imperfections”… these little mannerisms kind of add up. The car in front of you slows down a bit too much and gets too close to you (or you speed up a little too much so that you get too close to the car ahead of you), which causes you to slow down in your own way, which causes the driver behind you to slow down in their own way, and so on. Then, all the cars slow down, which leads to the first car that slowed down to speed up because now there’s a lot of empty loop in front of it, which causes the car behind it to speed up, which causes the car behind that car to speed up… until that first car gets a bit too close to the car ahead of them at the back of the congestion that it originally caused, which causes them to slow down, which causes the car behind that car to slow down, and the cycle repeats itself. In a loop of drivers, these slowdowns can form and disappear and form and disappear over and over again, even though the loop is clear and there are no obstructions along the loop. Each of these slowdowns is a phantom traffic jam.
I think this little piece of traffic modeling theory stuck with me all these years because it says something to me about the beauty of the fact that we are all people, with all sorts of imperfections — no — mannerisms, and out of these tiny, seemingly meaningless little mannerisms, things of great impact can appear to emerge mysteriously and bafflingly out of thin air, like magic. Simply because each of us doesn’t (and cannot) drive perfectly, we can create entire traffic jams out of nothing! We can jam up a perfectly open highway just by driving along it, the way it was meant to be used! And isn’t that beautiful in its own stupid (and I mean “stupid” in the most loving way possible), roundabout way?
______________________
From "quietly provocative" international best selling author and TV writer Jonny Sun, a weekly illustration and reflection on a personal object close to his heart.
Traffic model
