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Crowd density (people per square metre) and crowd flow (people per metre per minute) are relalated.
![Fruin](../../../_Media/fruin_med_hr.jpeg)
Which converts to the following density versus flow diagram (animated below)
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Which is often illustrated as the diagram below.
![Screen Shot 2012-01-15 at 21.06.05](../../../_Media/screen-shot-2012-01-15-at_med_hr-2.jpeg)
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Queueing
![Image3](../../../_Media/image3_med_hr.jpeg)
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And can be illustrated using the following space metric (feet and metres)
![Screen Shot 2012-01-15 at 21.07.17](../../../_Media/screen-shot-2012-01-15-at_med_hr-3.jpeg)
As density increased flow increases, but only until critical density is reached. This critical density can be different for different events/crowds. As density (people per square metre) increases above the critical density the crowd flow begins to drop. Crowd flow is also a function of the crowd order, armies marching can achieve a greater flow rate at higher densities than a mixed demographic crowd.
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We illustrate the flow versus density graph using both a colour and a graphic to show the density. A number of documents and standards use area per person. This can be confusing and we recommend that you always use people per square metre - it's easier to visualise and it maintains a clarity for crowd safety. The colour scale is also indicative of risk. To highlight this we run classroom demonstrations using a simple piece of string (area 1 square metre) and ask delegates to measure the time for a group of people to walk 10m. It's an illustrative experiment - but it highlights the curve shown below.
As density increased flow increases, but only until critical density is reached (2-3 people per square metre). This critical density can be different for different events/crowds.
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As density (people per square metre) increases above the critical density the crowd flow rate begins to drop. Crowd flow is also a function of the crowd order. For example, armies marching in step can achieve a greater flow rate at higher densities than a mixed demographic crowd. In other words, order in the crowd can increase the flow rate as shown in the 3 axis graph below.
![Screen Shot 2012-01-15 at 21.09.00](../../../_Media/screen-shot-2012-01-15-at_med_hr.jpeg)
Click on the links below for a video clip of: