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Let’s all be thankful and appreciate our friends, the good moments, expendable cash, and deep, deep discounts. Thanksgiving is here, followed by its thrifty cousin Black Friday—when crowds of people celebrate consumerism. If you have ever participated in Black Friday shopping, you’ve probably encountered the bottlenecks that are storefront doors. Like any problem in society we can be sure that science is there to find a solution. So, this Black Friday I’ll be thanking scientists for researching flows, clogging, and bottlenecks in human systems.


On Black Friday, bottlenecks stand between people and their precious goods. But more often, bottlenecks slow evacuation. Whether it be a fire or a mass shooting, there needs to be a way to move people away efficiently. Thankfully, many scientists study this process and have uncovered interesting conclusions, such as the “faster is slower effect”. If more than one human-unit can fit through a doorway, then evacuation slows.

In other words, an exit that is only wide enough for a single person is actually better for evacuation than one the width of one and a half humans. Of course, an exit that is two humans wide is still more efficient than an exit sized for one—but it turns out that, in stressful situations, humans become selfish and impatient, which leads to clogs if only 1.5 humans can fit at a time.

Understanding human behavior is an important component in reducing bottlenecks. Researchers often model bottlenecks on a computer because forcing crowds of people to exit a space under panic is somewhat unethical. To make these models, scientists incorporate parameters, such as “herding” and “individualism”—how likely are we to stick with the crowd, or to find another exit?

Other researchers have used animals as human crowding analogs. In one such paper, the authors used sheep. They state that “people and sheep usually behave in a very different way, because of politeness. But… in competitive situations, it is conceivable that people would shove one another selfishly.” Black Friday anyone?

Sheep and Goats Clean Up Travis AFB

The researchers marked the sheep with big red dots on their head, and then timed them while the sheep were trying to fit through a doorway. Strangely, placing an obstacle in front of an exit may actually speed up evacuation–as seen in this video.

This concept was known to help prevent clogs for coffee beans or rice entering a bottleneck, but this was the first time such an obstacle was applied to active subjects. The results have implications for improving evacuation routes in emergency situations, when humans become incredibly selfish—or, when we just really need that 55” 4K TV for $199 at Target. Seriously, have you ever seen such a deal?

We can’t expect human behavior to change, but we can better engineer buildings to compensate. Better evacuation routes can save lives, and in the case of Black Friday, so can better entrance routes. According to there have been 10 deaths and 111 injuries related to Black Friday since 2006. Although, to be fair, only one death was related to trampling–the other nine were caused by gun violence. On that note, we should be thankful for the science funding to conduct research into evacuation methods (because gun violence research funding is still banned). Let’s be thankful for the scientists and engineers who make buildings safer in times of emergency, and for science for always being a bomb-proof method of knowledge generation.

By Zach Decker

Posted by Science Buffs

A CU Boulder STEM Blog

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