## Fruin - levels of service

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Crowd density (people per square metre) and crowd flow (people per metre per minute) are relalated.

Which converts to the following density versus flow diagram (animated below)

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Which is often illustrated as the diagram below.

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Queueing

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And can be illustrated using the following space metric (feet and metres)

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.

Click on the links below for a video clip of:

2 people per square metre

3 people per square metre

4 people per square metre

5 people per square metre

5 people per square metre (marching in time)

6 people per square metre

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