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One of the crowd

Simulation software

New pedestrian simulation software is capable of modelling the impact of individual behaviour within a crowd, discovers Paul Wheeler.

Next time you are on the Tube or at a mainline railway station, take a good look at the diversity of the passengers.

Regular users will probably have tickets, know exactly where they need to go and pass through the network almost subconsciously. But then look out for the elderly lady with a large suitcase, a mother with three kids in tow or a group of tourists trying to make sense of an alien system. Their progress through the station will be very different.

Despite a wealth of guidelines and codes on the subject, predicting how people really use public spaces is a tall order.

Traditional pedestrian simulation approaches are based on demand estimation. In its basic form, this compares predictions of how many passengers are expected at peak periods with capacity through specific pinch points such as turnstiles and escalators, to make sure that codes are not exceeded.

Computer software that aims to provide a more holistic view of how entire systems operate is available, but until very recently such programs have had extremely limited capabilities.

Earliest models took a fimacroscopicfl approach, in which people's movements were simulated using the physical laws that govern fluid or granular flow. Next came fiheuristicfl or block models in which simple rules govern the behaviour of fisimulated pedestriansfl.

But these are restrictive in how they define a space, which is modelled in large blocks rather like a chessboard. Furthermore, they generally assume the pedestrian population and conditions in any given block of space are uniform. And the models break down when the flow is bi-directional and the density exceeds a relatively uncrowded two people per square metre.

While these models can be fitunedfl so that the analysis output matches real measured data - or, put another way, tweaked so they give the firightfl answer - they cannot give a realistic prediction of how people will actually use the space.

Try and apply these models to a situation that doesn't yet exist, such as a new station layout or to see how a space performs under increased crowding, and the analysis and its conclusions start to rely heavily on conjecture.

But a new generation of software looks set to change things radically. Microscopic simulation technology, as Guernseybased software developer Legion describes its program, takes the analysis down to the level of the individual.

Central to the program is years of research, carried out by Legion, into crowd behaviour. In particular, it has been probing what governs the walking behaviour of an individual and how this impacts on a crowd. Out of this research, Legion assigns fientitiesfl - as it likes to call the small dots that migrate across the computer screen during one of its simulations - with humanlike attributes.

Entities walk at different speeds and will have different tolerances to congestion; some will know where they are going, others will not and will migrate towards virtual information boards, and so on. Out of these finatural oscillations and interactionsfl, the entities break into a pattern of movement that certainly looks convincingly real.

Output from Legion is easy to understand by non-specialists.

For example, it gives simulations of crowds moving around a space in plan view. Colour-contoured plans show where crowding develops. You can even pick up the most densely trafficked routes through the system and identify dead space where nobody ever walks.

Once you know how a space works, you can start moving things around to assess what the impact will be. For existing spaces, this could mean repositioning turnstiles and ticket machines, while for new projects, it gives you the opportunity to test alternative designs in a way that hitherto has been impossible.

fiRelatively simple items such as the position of information boards and ticket machines have a big impact on how a space is used, fl says Legion CEO Martin Band. On the Tube network, where many stations are at or even beyond capacity, you can significantly improve the efficiency with which space is used.

This can even help extend working life.

Legion allows you to quantify the benefits of different designs in a very visual way, Band adds.

fiIt helps to identify hot spots and allows people to step back and look at a problem objectively. So you end up taking decisions on the basis of fact as opposed to opinion. fl And, says Band, fiorganisations using Legion do so because they can make savings in terms of both construction and operational costsfl.

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