Thursday 4 June 2015

Walking on Wembley Way - The FA Cup Final Arsenal vs. Aston Villa 2015 Gathering

Wembley Stadium. It has a proud history, some may say. It sure is an occasion, to go to Wembley for any event, but of all events, the FA cup final is probably the biggest event on the Wembley Stadium Calendar.

As fans travel to the Stadium from all across the country, the majority arrive at Wembley Park Station, making their way along Wembley Way, as it's traditionally called by fans. The official name being 'Olympic Way' of course, as if you didn't know. I'll be using 'Wembley Way' and 'Olympic Way' interchangeably in this post.

Note: As this is a fairly long post, you may want to check out the videos first before going ahead, they're interesting.


Lets start with a little background, about this little 600m (approx.) stretch of land from Wembley Park Station towards Wembley Stadium. Fans would know it as a pedestrianised easy access route towards the stadium. It never used to be that way. The Wembley Stadium area started to be formalised during the Empire Exhibitions of 1924, later being redeveloped for the 1948 Olympics. In fact, the famed route towards the stadium comes from the labour of German prisoners of war during this time, shocking, I know. It was re-built in 1948 during redevelopment work around the stadium to host the 1948 Olympics, hence the name 'Olympic Way'. The Wembley area, hasn't remained static, and over the years, it has evolved fairly consistently. It has been through several phases of development, and has also been fully pedestrianised, where at one time traffic used to be allowed. Today, the experience that unravels when walking along Olympic way towards the view that is presented of the centrepiece Stadium and it's iconic arch, is what makes the experience unique to Wembley, and one of the many reasons why this Stadium has become as recognisable a destination as it is.

The Arch of Wembley Stadium (Source)

The FA Cup Final

The FA Cup Final, that's what we are here for. It's Arsenal vs. Aston Villa, the culmination of months of tournaments, the build up, the excitement, the emotions are all here to be displayed, with a few fans being asked to tone down by the police, and as the crowds arrive, just standing there, you can't help but be drawn into the build up. Fans, both of Arsenal, and Aston Villa, chanting, the Wembley chants. Oh my, it's exhilerating. Sadly, I'm not going to be in the Stadium, I'll be watching the crowds arrive, afterall, this is a blog about crowds, but it's hard for the excitement not to rub off on you.

Crowds Arriving

It's 3pm, as I arrive along Bridge road, as the name implies, is a bridge that stands over the station edge of Olympic Way, and gives a direct view of Olympic Way, with the Stadium in the distance. You can use the embedded google map above to zoom in, and see it from a satellite view. The fans are already arriving for the 5.30pm kick-off, and a constant stream of people arrive until kick-off time, with a few late ones running along the way. It's time for me to take some videos and photos of the crowds, as we shall see, it would be great to observe the behaviour as crowds arrive, the pedestrian traffic management employed by the police, as well as any other nuances that can be extracted from the crowd flow. We'll also observe the crowds leaving later on, don't worry.

Crowds Arriving along Olympic Way (View from Bridge Road)

As the trains arrive at the station, there's a surge of people arriving, walking down the stairs of the station, and along Olympic Way, it gets really busy, I mean really really busy. Here's a video below of what it looks like around 3.30pm to 4.05pm, that has been hyperlapsed.

Hyperlapse is a technique that takes into account both temporal and spatial features, so in a sense, it's a time-lapse with video stabilisation. I'm using Hyperlapse software by Microsoft Research, that approximates the user-specified video speed-up, and provides a smoothly moving camera. Useful, when you're recording by hand. As an aside, if you're interested in the background of how they're created, Microsoft are presenting a paper at SIGGRAPH 2015, as well as one they presented in 2014. In my case here, it really helps with the camera shakes as the videos were taken by hand.

Anyways, coming back to the actual video, the nice thing about the hyperlapse, is that it has the unintended consequence of slightly slowing down the video when there are abrupt changes in the crowd flow, such as bi-directional lanes forming, or changes in flow. There are several crowd phenomena that can be observed, especially as this is a fairly unique set of circumstances coming together, such as the culmination of an event, a direct route, a singular flow i.e. almost a procession along a very wide pavement, along with a very large number of people, given that Wembley Stadium has a 90,000 seating capacity. It makes it easier, to extract phenomena and behaviours in the crowd at individual stages. We will see how our individual decision making behaviours emerge, blending and transition into something bigger, than any one individual.

Emergent Behaviour

First of all, due to the unique set of circumstances, almost everyone in the crowd has similar sets of desires i.e. to start at Wembley Park Station, walk along Wembley Way, and enter the Stadium. 

Due to the common set of desires, individuals tend to give up their decision making power, and lose their will to the will of the crowd, or as described by social psychologists, de-individuation, where one becomes part of the crowd, this is the nicer version, of the term mob mentality. There are several sub-processes that take place in the process of de-individuation and becoming part of the collective, that is, the crowd. Although, I've briefly explained some of the emergent behaviours in a previous post, I'm going to go into a bit more detail here, and also discuss it in the context of the crowds on Olympic Way.

 Herding (Following)

As people arrive around 3pm, the crowd is fairly sparse, as shown in the beginning of the video, individuals have a much better view of the surroundings, they have an idea of their goal, and are able to take their own decisions of where to go. However, as time goes by and the density of the crowd starts to increase, it becomes difficult to be fully aware visually of what lies ahead of you, this is the first stage, and the clearest stage where one can actually observe how the behaviours transition from the individual to the crowd. As I mentioned earlier, a unique set of circumstances have come together, the fans in the crowd have a common goal, and as the density increases, the individuals will transfer control of their actions and behaviour over to others in the crowd, specifically to the person in front of them, if their destination lies in front of them, and in a similar direction. Aha, you say, yes, this event works really well for that, as the goal is Wembley Stadium, and it's a common goal in the same direction, although the eventual goal, is the goal of the football (bad joke!). Moving on, the passing and transfer of the decision-making to others and following their lead is termed as social contagion (see also here and here for more info). As you can see, each person in the crowd similarly starts to follow the individual in front of them that is travelling in a similar direction, leading to conformity. This conformity is termed as herding behaviour, which starts to emerge. In essence, we become a herd. Here, you're not making your own decisions anymore, and there's a bigger power that no one person is in control of, making these decisions for you. I know, we all like to be in control, but sadly, as much as we like to believe, we're in fact, not.

The Zipper-effect

We're done with herding, now what? Well, it's time to zip your jacket, no I'm not joking. What happens now is that, as the crowds arrive, the density increases, the herding behaviour is still in tow, where each person (or group of people) in the crowd, are following individuals in front of them. This herding behaviour leads to multiple layers of pedestrian flow forming, travelling in the same direction, and starting to cover the width of Olympic Way, as you see further into the video. These layers are compacted like a zip. Let me try and explain, the typical width of each layer, it has been noted, is approximately 45cm. However, the approximate width of a person is 55cm. What happens here is that, as each individual is fed through in a densely packed crowd, for example, if I were walking through the crowd, typically I wouldn't walk exactly behind the person in front, but in the middle of two people in front of me (presumably in order to see ahead, and fill the gap between the two people), the people behind me are doing the same, creating an almost zig-zag pattern, just like the layers of a zip, with me being one of the zipper teeth. Hence the term, the zipper-effect.

Lane Formation

Through the zipper-effect and herding, we lose control of our decision making, and put a lot of trust in the individuals in front of us in order to guide us, as the people in the video do. These zipped layers, lead to lanes forming that we wouldn't be fully aware of, whilst walking through the crowd. These lanes are not constant, but break and merge to adapt to the environment the crowd sees itself in. It may not seem completely obvious from the hyperlapsed videos, so I've also motion blurred time-lapse photos in the video below. You see how, there are several multiple layers of flows during the arrival of people walking along Wembley Way as they walk towards the stadium. The multiple layers are also known as stripe formation.

You can actually see the breaking and merging of these lanes in the motion-blurred video. During the 1 hour period, some fans stop to take pictures, as it's a good place to frame a shot with the Stadium in the back-drop. When these fans stop, within the motion-blurred video, they start to stand out. In the context of the crowd flow, they take the place of temporary obstacles. Now, in order to avoid the obstacles, some of the flow lanes break and merge, in order to navigate around the fans that play the role of temporary obstacles.

These standing people also have a secondary purpose, they actually funnel the crowd flow, although not necessary for the flow in this case, it actually helps to ease the pressure in the flow if it is building up, as it breaks up the flow. We'll see how this phenomena is used for a much more practical purpose, when the crowd are leaving.

Other Observations - Crowd Flow Control

In addition to the hand-held video shown earlier, I was able to use a DSLR on the railings (sadly my tripod turned out to be too short for the railings). Anyways, managing to take photographs over 1 hour at 2 second intervals, until kick-off time, the pictures have been cropped to focus on the police line, and have been stitched together in order to create a time-lapse video. However, the intervals didn't seem short enough, so it was necessary to motion-blur them, again to bring out features that wouldn't be too obvious otherwise. The video is still not very clear, as the upload caused a loss in quality, but hopefully it will work for now.

Police Spine Ramp Funnelling

The cropping has allowed the video to be zoomed in to observe the role of the police, as the crowd approaches the stadium, and the motion blurring help in extracting the changes in the flow. The line of police standing in the middle, serves an important purpose. As we all approach the stadium, it becomes exciting, or as some fans put it, the atmosphere is electric, the sign boards just above the police line display the direction to head towards based on the type of tickets purchased (as shown in the image below), in order to get to their respective seats. If there was no police line, the lane formation I described, will start to form, break and merge constantly, typically along the middle length-wise, as each of us try to go towards the ramp in the direction the sign boards direct us. This breaking and merging would increase the interaction between individuals as we tend to collide whilst trying to change directions, and in turn, the collisions start to slow the crowd.

The signs showing 'Aston Villa Collections' direction along the right ramp

The police line doesn't necessarily stop the crowd flow lanes from changing direction. However, the police line serves as a form of resistance to changes in the flow, and hence funnelling the crowd flow on each side of the line towards the ramps on their respective sides.

Why is the presence of the police line successful in creating a resistance, despite the gaps present for individuals to pass? Well, it's a cost / effort ratio. There are two conflicting sets of desires. We can see it from the individual point of view, as well as the flow point of view. As an individual in the crowd, say if I'm on the left side, I see the sign directs me to go towards the ramp on the opposite side (just as the Aston Villa sign in the image above does). I see the police line, and I see the direction of the crowd flow going in parallel to the police line. Is it worth trying to work my way through the crowd in order to get to the ramp on the other side in addition to getting through the additional narrow gaps created by the police line, against the momentum of the crowd flow that is leading me to the ramp on the left which will eventually get me to my seat anyway, probably not? Unless, I'm really determined, but what is the point?

From the crowd flow point of view, most individuals allowing the momentum of the crowd flow to direct them leads to parallel flow lanes appearing. In addition, the police line breaks the flow along it's width into two at the middle, leading to the flows on either side funnelling to the ramps on their respective sides. One point to notice though, is that the flow lanes near the police line have a smaller resistance due to the gaps in between the policeman. As those lanes don't need to fight against the other flow lanes, and where the gap between two individual policemen is greater (specifically in between two poles, the gap present between the last policeman and the pole), the effort required to change sides is much less than at any other point. The consequence is that you tend to see the flow lanes changing in these areas of broader gaps, which is not a big deal, where the important job of funnelling the crowd towards the two ramps, evenly distributing the crowd flow has been achieved.

Natural Crowd Surge Control

This is an interesting one. The crowd pressure is actually controlled, quite naturally. There are regular surges in the crowd flow at certain intervals coming from the station and going towards the stadium. Yes, you guessed it, controlled by the train timetable. As the trains arrive, the crowd flow surges, before dying down. These regular stop-gaps in the arrival helps in distributing and dispersing the crowd as they arrive, and it can be safely assumed that there won't be any unusual spikes in the crowd flow. This is really helpful in ensuring that pressure doesn't build up in the flow, helping to prevent any tragic events that have occurred in other situations, where other phenomena, such as Stop / Go Waves, and Turbulence can occur as pressure builds up (see here for more info). We'll see a similar stop-gap situation as crowds leave, but one that is artificially created.

During the FA Cup

Now that we've assessed and observed the crowds arriving, it was time to go to a bar in the Stadium retail area where I asked a friend to meet me, enjoy a beer, and watch the match from there. It was great even if it was just watching it from a bar, as you can actually hear the crowds roaring as goals are scored, well, mainly the Arsenal fans, as we know what happened. Well, during this one-sided match, as the last 10 mins approached with the score at 3-0 to Arsenal, it was time to leave, as I sensed that the Aston Villa fans would be leaving. As I was briskly walking along Olympic Way, becoming part of the crowd, following those in front of me and forming lanes (that I couldn't see), I heard another roar from the Stadium, as Arsenal put the final nail in the coffin with a 4-0 lead, and on their way to becoming the FA Cup Champions. If you want to watch the trials and tribulations of some fans, you can watch a BBC program 'Truly, Madly, Wembley' available on the iPlayer for another 6 days (UK viewers only, I'm afraid).

Crowds Departing

This time, as I approached Bridge Road, the stairs leading to Bridge Road were blocked off by the Police, so I had to go under it, and over to the other side, and get onto the road from the Wembley Park station area. The Police were standing on Bridge Road, so wouldn't allow me to take photos from the railings. Having to stand back and take the videos without any support, you can see the camera shaking as I get pretty tired towards the end. It's a video taken over approx. 90 mins. The hyperlapse video below has around a 20 min segment cut off from the middle, as it didn't show anything different to what can be seen.

Observations - Crowd Flow Control

Arsenal winning the match

In the video, as can be predicted, you see the Aston Villa fans leaving first. Until Arsenal lifts the FA cup within the stadium, the majority of fans leaving are Aston Villa supporters, followed by a few spots of yellow and red with Arsenal fans starting to leave, with the majority at the end being Arsenal fans. In a sense, the events of the match has implicitly controlled the departure of the crowd towards the station. 

It's only a limited control, but helps, however, the departure of fans is pretty constant, and as the match finishes, the departure rate of the crowd can cause pressure to build up as they head towards the station, with the rate of departure of the trains being slower than the rate at which the fans leave the stadium. There is no other natural stop-gap departure rate that we had during the arrivals, such as the one provided by the train timetables.

Stop / Go Simulation 

Crowd management staff are therefore employed to control the crowd flow towards the station. They serve the purpose to control the crowd by employing Stop / Go signs. As Wembley Park station gets congested, the staff switch the 'Go' signs to 'Please Wait'. Hence simulating a stop-gap departure rate that provided natural crowd surge control, provided by the train timetable during arrivals earlier in the day.


There's a consequence of the crowd management staff regulating the crowd flow. They start providing a secondary purpose - funnelling the crowd flow. This funnelling actually helps in decreasing pressure in the flow, when the density is high, and could potentially help in an evacuation scenario. As it has been known to show that narrow obstacles can actually improve the flow at an exit by preventing pressure building up in a flow. I may be wrong, as it's not exactly an exit. The video above doesn't show the funnelling quite as well as another source I found from a reddit thread that I attach.

The video sourced from the redditt thread, shows a time lapse loop, with police horses in control of the crowd management, on different event.

Staircase blocking 

Crowds tend to flow towards their destination, and try to find the path that requires the least amount of effort. Especially in our case here, everyone wants to go home, the match is over, and they want to get back home as quickly as possible. As pressure builds up along Olympic Way, the crowd flow will try to find other openings or gaps that would allow it to reach it's destination i.e Wembley Park Station. These gaps are the staircase that leads onto Bridge Road, and across towards Wembley Park Station. You can see the staircases on the right and further down on the left in the video (a google street view looking towards the station from Olympic Way with Bridge Road overhead has also been attached below). This has the potential to cause chaos on the road, as vehicular traffic tries to pass at the same time, causing traffic jams. Therefore, the police block these staircases, and form a path of resistance that doesn't allow the crowd onto the stairs, unless, some people get a bit unruly of course, then that resistance can break down. The crowd here were pretty well behaved.

Over the 90 mins, these four processes help a generally smooth exit for all the fans towards the Station and on their way home without any chaotic effects. The only downside is that they have to wait. Afterall, the Stadium has a 90,000 seating capacity, out of that say 80,000 were occupied, and another 20,000 to 30,000 went home by other means, that still leaves around 50,000 to 60,000 fans taking Olympic Way towards Wembley Park Station. Based on the capacity and safety measures taken, it's reasonable to wait 20 to 30 mins in order to get home safely.

The last trickle of fans leaving Wembley

The Analogy with Fluids

I've talked a lot about the crowds in terms of density, pressure and flow. It almost sounds like a fluid flow. Do crowds behave as fluids? Well, to a certain extent they do, however, humans are sentient beings, able to perceive and feel things. I talked about the properties of emergent behaviours, and how individuals transition from taking their own individual decisions to then passing on control to the flow of the crowd. The individual in the crowd is guided by many different desires and factors as well as the emotions that are brought out whilst in the crowd flow. They pass control, and they take back control depending on the situation that presents itself. We see how fans stopping to take pictures with Wembley Stadium in the back-drop in order to create memories that will last a lifetime. This ability to take our own decisions is where the analogy with fluids breaks down, where we stop being particles, and become human. We can try to look at a crowd flow as dispassionately as possible, however, there is still a human element to it, and we need to be aware of that. Every individual has a different history that guides them to do what they do, conflicting between wanting to be in control, standing out from the crowd, and being part of the collective. This is what makes predicting crowd movement such a difficult problem, and so difficult to simulate. However, simulation is a simplification of reality, and if we try to draw an analogy with fluids being aware of the limitations, we can use it to a certain extent in addition to other techniques to predict the flow and movement of crowds.

Self-organising Behaviour

There's another phenomena I want to discuss. Looking at crowds with a naiive eye makes it look rather chaotic, or we can replace it with the word 'complex'. I've talked about emergent behaviours within a crowd, where the individual behaviours lead to a collective crowd flow. This transition between the individual person to a collective flow pattern, transitioning from herding to zipping to lane formation and back to the individual, with lanes forming and merging, and the crowd trying to fill gaps in its route with the minimum effort sounds like a 'system' doesn't it, where if you think about it, the flow is fairly well organised, without having to control it much. Just ensuring it's guided in the right way as the police and crowd management staff do, the crowd flow will form naturally without much effort, self organising itself for the situation that is presented. This leads us to observe that complex individual behaviours driven by the human mind leads to a system that self organises itself given the environmental / urban sitation at hand. Something that we can now call, 'a complex system'. Isn't that interesting?