Using BIM to turbocharge crowd analysis – and vice versa


Compare the typical, idealised architectural illustration of a proposed new building with its carefree people with the reality we often see in our cities with queues and congestion at peak times. Crowd simulation at the design stage can mitigate and even eliminate these bottlenecks and ensure that the building is as functional as possible at all times.

Crowd simulation software is not in itself new – it’s been around for 25 years or more and is backed up by academic research and empirical observation. However, the move to 3D design with BIM means that there’s a growing wealth of data that can be brought into simulations, making them ever more realistic and reliable. The latest release of MassMotion enables teams to combine 2D and 3D CAD assets into a single comprehensive 3D model.

In truth, the Romans had the core concepts in hand. A few years ago, the MassMotion team ran a comparison of the Colosseum in Rome with the Beijing National Stadium – designs separated by 2000 years of culture and technology. They found that both stadia would take around 15 minutes to evacuate. In short, the Romans had cracked the basics, and indeed we still use much of their thinking today.

So why do we need the breadth and depth of analysis tha MassMotion offers? Well, today we are faced with bigger and more complex crowds and an urban fabric is so dense that it is very easily disrupted with immense knock-on effects.

So, it is essential that, as well as we considering how crowds behave within the structure, we look as well at how new buildings or refurbishments and he people that use them will affect their neighbours. Crowd simulation has a role to play not only at master planning stage but also during construction works and throughout their useful life.

Take new York’s Fulton Center where designers had to integrate six lines tha had been built independently with no thought for future integration or, indeed, the enormity of future passenger load. The refurbishment of Toronto’s Union Station, is due for completion in 2019, after nearly a decade of what could have been unbearable disruption without pedestrian analysis to assist construction staging. In Europe, the multiple stages of the transformation of New Street train station in Birmingham UK was managed by the UK’s Network Rail using MassMotion and without disruption to essential rail services.

Both projects have used MassMotion to streamline a multi-faceted project and, because the models are easily queried, to experiment with different ideas and manage both costs and  unexpected scenarios.

How crowd simulation evolved

Early crowd analysis software provided basic block simulation, looking at the adjacency of spaces. Next came 2D vector-based grid systems with more dynamic interaction between people and their environment; and we started to see the introduction of social forces models and autonomous decision making by agents within simulations. Now we have 3D agent-based models with very sophisticated interactions in models that replicate real spaces with continuous geometry: rooms and floors are linked with doorways and staircases etc and the agents make decisions based on the whole environment. You can follow individual’s entire journey as they make their way between different areas and levels.

All of this development is underpinned by academic work on human behaviour in crowds. Back in 1971 John Fruin’s PhD thesis established six levels of service, the characteristics by which we judge the comfort of our space. These range from moving comfortably and unimpeded to shoulder-to-shoulder gridlock and are still key touchstones for crowd analysis.

Throughout the world, the London Underground Station Planning Standards, the US NFPA fire standard, and the Green Guide for sports grounds are the main standards designers adhere to – the de facto rules.   There is also a growing body of verification and validation standards that simulators are expected to use and confirm to: the National Institute of Standards in the US and the International Maritime Organisation are the generally-accepted markers of quality assurance.

Simulation always starts with the concept of an agent, and these simulated people have become ever more sophisticated and autonomous. They are programmed with physical properties such as size and speed, an agenda such as a flight to catch or a burger to buy at half time, and preferences about whether to take stairs or escalators. The algorithms behind this are steeped in academic research on natural preferences not to bump into things or take huge detours and on how flow rates vary with density (and it is not a simple linear relationship). In MassMotion, you can add to that local requirements and venue-specific data on, say, transit timetables and capacities of platforms and ticket and security gates to simulate complex journeys through a facility.

In a nutshell, the decisions agents take about their next move are governed by the cost of alternatives. What is the optimal distance to be travelled? Are there stairs? Is there a queue?  Is there an opposing flow of people coming towards them etc.

In a MassMotion simulation, they make choices about their route dynamically, in response to the environment around them as it changes. They will avoid congestion, take advantage of faster moving queues etc. They will not necessarily do what design engineers want or expect them to, instead they will give a picture if what will happen that is as near to real life as possible. Unlike other tools commonly used with CAD packages to provide animated visualisations of designs, or simulators that might tell you there will be a bottleneck but don’t help you solve it, MassMotion puts intelligent agents in the model and enables you to experiment with new scenarios.

The BIM bonus

Running simulations involves importing and storing large amounts of data – and that has often been the most time-consuming part of the process. Adding building objects like doors and escalators was done manually.

Now, with IFC as a reliable and vendor-neutral way of getting information into simulation tools like MassMotion, import/export is simply no longer an issue. We can focus on what we do with the data available to the simulation, and not worry about the logistics of getting it in there.

BIM turbocharges the whole simulation process because we can import not just 3D geometry but whole BIM objects. So, where there are floors and stairs, the simulation software picks up on the metadata and recognises these objects for what they are. It immediately understands where they are and how they will affect the journey costs that are perceived by agents without the need for hours of additional data input. MassMotion algorithms go through the geometry to work out adjacencies of spaces and building features, and to map out the alternative routes available to agents.

There may be a few anomalies, like a stairway slightly offset leading to a brick wall or thin air, but with the option of 3D visualisation you can do an immediate sanity check and they are obvious to see. In any case, MassMotion spots and highlights them, so you can pretty much drag-and-drop until the feature goes green on screen, letting you know the exception has been resolved.

If you spot congestion on screen, you can try creating a bigger or second link – a wider gateway, or a second door perhaps - and MassMotion with calculate new route options and test them on crowd with its specific agenda. Once the underlying data is imported, you can quickly see results of these complex multi-threaded calculations testing different scenarios in minutes rather than hour or days.

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