Designing for human unpredictability

Systems are designed for maximum efficiency and optimised performance, but the unpredictable nature of human behaviour can act like grit. How can design predict and solve this? 

It’s 6pm at the end of a busy day and all that stands between you and dinner is the drive home. You get in the car and hit the road.  All is going well before the brake lights appear in front of you and everything grinds to a halt. You scan the traffic news for information on roadworks or an accident but nothing. Eventually the traffic starts moving again…but you’ve just added another 20 minutes to your journey.


This will be a familiar scenario for many of us. It’s been well researched that, even in heavy traffic, if all cars moved at the same regulated speed, traffic would keep moving smoothly and we’d actually all get home faster. What produces these phantom traffic jams is the difference in speed – once a driver has to brake, the car behind has to brake slightly more heavily and so on until cars, sometimes a mile back, come to a halt.

Even though most of us assess ourselves as good or excellent drivers, the braking that comes from our behaviours snarls up the system.

The biggest obstacle to improving highway congestion is the behaviour of drivers themselves, not the design of the highway. 

It is an example of a system with many variables and moving parts. But it is also a system where the human ‘actors’ are often the weak point and their variable and unpredictable behaviours are drags on system performance – we are the grit.

Airports face somewhat similar challenges. In the 2019 IATA Global Passenger Survey, 79% of passengers reported that to clear immigration and customs, including security, 10 minutes was the maximum time they’d want to wait. Security is a top pain point both for passengers and airports. The longer passengers are waiting in line for security, the less satisfied they become with their airport experience. For the airport, every minute a passenger spends in security is a minute they aren’t spending in retail, food & beverage; important because retail is follows security and research shows stressed customers spend less. When it comes to airports, time really is money. 

Image: Smarter Travel

For airport security there are, of course, limiting factors – the volume of people, the number of screening lanes and the speed within which the  equipment can successfully scan a tray and decide if it passes or fails. 

Human behaviour is a variable in any system. In airport security the frequent grit in achieving the optimum flow rate for any particular airport is what the passengers do in that process. 

A Northern UK airport recognised the importance of streamlining this process by examining passenger behaviours. We worked with them explore this, and see what changes we might make to help passengers to help themselves, and thereby help the airport. 

CCD’s research team spent several days in security observing passenger behaviour and analysing CCTV footage to identify common patterns. Many airports have tried various initiatives to look at speeding up how passengers unpack at the start of the screening.

We found that to maximise the flow, you need to move the trays and their contents away from the conveyor, and observed a number of behaviours at the re-pack end that negatively impacted passenger speed and herd behaviours as they moved through the process.

We broke down our insights on behavioural traits observed in the security re-pack area into the following passenger profiles: 

The Belt Hoggers who repack at the conveyor, don’t return their tray and are oblivious to the impact on other passengers.

The Considerate Collector who gets out of the way quickly, returns their tray and might even return some empty ones while they wait.

The Pocker Packers who are travelling light, maybe with no hand luggage. They are usually just grabbing a few items from the tray and therefore do this at the belt

The Worker Bee who clears all the empty trays. They are probably a frequent flyer who knows the system and that getting these out of the way will get their tray through faster.

The Slow and Steady passenger who takes their time making sure everything is correctly stowed back in their bags. They usually take their trays away to get themselves sorted with a bit more space. They might also look for somewhere to sit, especially if they’ve had to remove their shoes

The Camped Convoy coming through in a group, probably with lots of liquids or cosmetics. They move as a pack so only clear out of the way at the speed of the slowest person in the group.

Airport security
Airport security tray

Breaking behavioural traits into profiles helped us to identify which specific passenger behaviours needed to be nudged to behave better, and which needed encouragement. 

Passengers aren’t trained on the security process. It is all based on previous experience, which might be minimal, and by following what other passengers do.  Similar to our earlier example of phantom traffic jams, the impact of this can be significant as there is a clear ripple effect from individual behaviours.

This herd mentality was prevalent in the re-pack area. If a Worker Bee started clearing trays, so would others . One Belt Hogger could slow the whole process: un-returned trays start to create a backlog, slowing the delivery of scanned bags and creating a congestion of waiting passengers. This ultimately slowed the input of passengers through security at the front-end, and meant longer waiting times in the queue.

Sometimes there is information to encourage certain behaviours and/or direction from staff. But in our experience, this is inconsistent both between airports and, in the case of staff, between individuals.  In the main, the passenger acts independently with little of assistance from staff. 

There are a number of areas for intervention that we explored including how we might nudge passengers to take their trays to a separate repack area and then return the empties, how the design of that area might positively influence that behaviour and make repack easier, and how might we involve staff to do more than just be security agents and provide positive advice and assistance.


David Watts

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