Social Forces Model with Human participants on the BBC

The BBC's science series 'Bang goes the Theory' recently had an episode on crowd behaviour. It shows a fascinating way of getting plenty of research out there into the public eye, using very short clips of research taking place based on certain themes. Anders Johansson, who still works with CASA, ran an experiment based on the 'social forces' model.

To give a heads up, the social forces model is an agent based model that simulates the microscopic movements of pedestrians. The motion of these pedestrians are described by subjecting them to 'social forces'. These forces are exerted by the pedestrians personal environment, as well as the interactions with other pedestrians in this context.

The movement of these pedestrians governed by these social forces are defined by the equation below:



If you'd like more details on the paper, it can be found here

An example of a social forces simulation model can be seen running in this video below:




Now, with this BBC episode, you can check out this model in a real world example with the help of an experiment with human participants, where you can see the effect of jams during an evacuation in a potential real world situation, and how a very simple solution of placing an obstacle at the exit can actually improve the flow of people through a door when evacuating a building. Although, your intuition I'm sure would say that it would not make sense. Actually, as this obstacle separates the flow of people, it prevents a jam occuring at the door, and therefore, creates a smoother flow through the door. Have a look, it's available for another 10days, and the experiment runs from around the 24 min mark, UK users only I'm afraid:

BBC Bang goes the Theory S6 Ep 4

Enjoy!

Tube Strike: A changed Macro-System

The recent tube strike and a discussion with one of my professors has led me to think about micro and macro systems as a whole, and in turn simulations working within these constraints.

First of all, let me say a little about a normal working day and what happens during this time. We have a fully working transport system, a nice sunny day (or mostly grey, in London at least!), a phenomena, if you'd allow me to call it that, takes place i.e., commuting. Individuals work, that's how the economy and you, as an individual survive and provide for yourself, and your family. So, we have people who commute to and from work everyday. What happens during the commute? Each individual, makes an independent decision in order to reach their work destination. How they get there is based on personal choice, which is generally ruled by the amount of time it would take to get to work, the distance to workplace, and the number of changes that are required. This decision gets refined as the individual finds him / her self making the most efficient decision to reach the workplace.

Each individual takes these similar independent decisions becoming routine over time. Aggregating all these independent decisions together, we get people moving around, and a pattern develops as the micro-system stabilises, in which ways people move to commute to and from work. These hundreds of independent decisions are taking place within the constraints of a macro-system. The macro-system in play here is the transport system, and these individuals actually play by the rules set out by the macro-system in place here.

A macro-system can be defined here as a large system within which micro-systems are contained. Therefore, here, we have the transport system as the large macro-system, and the individuals as the micro-systems which are contained within this large system, and taking their independent decisions within the constraints set out by it.

Now, we have a tube strike, like the one on 3 November 2010. What happens here?! The large macro-system changes. Most tube lines don't work, sever delays on lines that do, more buses on routes, cycles being transported more frequently to fill up empty slots. This creates havoc in the micro-system, but it doesn't fail. In fact, what happens is that the micro-system adjusts the way it works within the new constraints set out by the macro-system in play, and then we have the same individuals making their renewed complete independent decisions, again taking into account the most efficient way to get to work by finding the lines / buses / boats that are working, and taking those transport links, or replacing it with cycles or cars. We now have a micro-system changing, but in a way that individuals still get to work, but using the new constraints set out by the macro-system at play, and they work within these constraints. Complaints? Yes....Impossible? No, not at all!

It's the laws of the macro-system here. Micro-systems are contained within it, and they will change in order to work within the constraints of the macro-system, or even be influenced by it. An analogy with Ecological Systems Theory can also be drawn, but I'll leave that for another post!

This is the problem I wonder about when I'm designing my model, I need these micro behaviours to work within the constraints of the macro-system at play. Do I model the macro-system first, or model the micro-system and build a macro-system around it? It's the chicken or egg problem again here!