The Theory

The Surprise and its crucial role in accident causation.

by Duncan Mackillop


If there is no surprise then there can be no accident is the fundamental point at the heart of the new view of road accident causation. For many decades people that have concerned themselves with the problem of road accidents have struggled to deal with what appears to be the enormous complexity of the interactions between people, vehicles and the road environment. This complexity has tended to disguise the fact that there is a simple set of underlying rules that explain all of the observed phenomena and which will provide a framework for future study. No surprise-no accident at first seems to be far too simple an explanation for the observed complexity yet as Occam’s Razor states “among competing hypotheses, the one with the fewest assumptions should be selected”.


No surprise-no accident contains just one assumption, but that assumption is based on a great deal of understanding about human brains and their function and limitations and how those brains integrate with and manage complex and dynamic systems.


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To fully understand the nature of surprise it is essential that some fundamental facts about brain function are clearly understood because if you understand brains then you understand everything!


Movement and Memory  


The reason we actually have a brain is for the creation of complex and adaptable movement and the bit that makes us human works by making predictions based on sequences of movement patterns stored in and recalled from memory.


At first glance this might seem like an overly simplistic explanation of what is considered to be the most complex organism in the known universe, but it is essentially correct. The only way we can actually affect the world around us is by moving as without movement we couldn’t hear, speak or see, we couldn’t eat, reproduce, have fun, ride motorbikes or do the million and one things we take for granted as a human being. The majority of our sense organs are primarily designed for the detection of movement in the world around us or within our own bodies. Our eyes detect the movement of objects and our ears detect the movement of sound pressure waves in the air, the touch sensors in our fingers are attuned to the way in which our skin moves when it comes into contact with an object and stretch sensors detect the movement in our muscles and viscera. The ability to move our bodies and sense organs allows us to detect objects which in themselves are incapable of movement. Our eyes exhibit extremely complex movements all designed to pick out moving and stationary objects in the world around us even when we are moving through that world. The ability to detect all these patterns and sequences of movement in time and space makes it possible for us to store them in a memory system that has specifically evolved to handle such patterns and sequences.


The bit of the brain that we are most interested in is called the neo-cortex which is the wrinkly thing that we recognise as being a brain even though there is a lot of the actual brain buried underneath it. The neo-cortex is basically a thin sheet of cells called neurons that if you were to flatten it out would be about the size of a tea-towel. Underneath this sheet of cells which is usually called grey matter is the white matter which is all the wires and cables that connect the neurons in the neo-cortex with other neurons and other components of the brain and nervous system. Underneath the white matter is the limbic system which is a very old part of the brain and one that we share with animals like lizards etc. The limbic system plays a significant part in processing motion as well as providing all the chemical generators that drive things like our emotions etc, but it’s with the neo-cortex that the most important memory functions lie.


Thanks to one Isaac Newton we now know that all motion follows certain immutable rules, yet it would surprise you to know that a three year old child is fully aware of these rules and the resulting limitations that they place on the world. The fact that objects move through time and space according to fixed rules means that the patterns they form and the sequence they form in can be stored in our neo-cortex. The act of reading these words is sending a stream of patterns in sequence from your eye into the visual cortex at the rear of the brain. The way in which the brain is wired means that the sequence of any pattern coming in is instantly compared to a pattern sequence that the brain has seen before and has previously stored in memory. This is the mechanism by which we learn things and it is also the mechanism through which we remember things as well. If the incoming sequence of patterns matches the sequence of patterns we have stored in memory then we recognise the pattern, however if the incoming sequence of patterns does not match anything we have stored in memory then we know that what we are sensing is something novel.


By having patterns in sequences stored in memory it then becomes possible for us to be able to take from memory the next bit of the pattern sequence even though we might have currently sensed only the first bit of it. For example when you read the pattern sequence ‘how now brown’ your memory will see if it knows of a similar pattern and retrieves it along with the remainder of the pattern sequence. As you read ‘how now brown’, the neo-cortex remembers that usually when this pattern is encountered the word ‘cow’ immediately follows it. Again for the pattern sequence ‘the cat sat on the’ the word ‘mat’ is the most often experienced completion of the sequence and so that’s what the memory delivers. By way of this mechanism we are able to predict ‘what happens next’ in any sequence so you can reliably predict for example what word is missing from the end of this ___. Predictions are happening all the time in the form of IF pattern sequence (a) THEN what normally follows is pattern sequence (b) and so on.


What happens though when the initial sequence of patterns matches the one recalled from memory, but the subsequent pattern does not? What happens when rather than reading ‘the cat sat on the mat’ we read ‘the cat sat on the cow’ or ‘how now brown mat’?  The cat sat on the cow is not a statement of the impossible yet for some reason it appears wrong to us because what has actually occurred is not what we had predicted to occur. That wrongness is indicated through the mechanism called surprise.




Without prediction and surprise everything that’s possible would be entirely probable and we would think nothing of it. See a person with an ear where one of their eyes should be? Prediction and surprise would normally bring us up short as ears should be where ears should be and not where eyes should be. When we scan a face we first locate one of the eyes and then because we have seen the sequence of patterns before we can predict that if we shift our gaze slightly one way we’ll see another eye and if we shift it the other we’ll see an ear. As our gaze moves around the face the bits of the face appear where we expect them to appear. They may be slightly different shapes, sizes and colours, but they will be instantly recognisable nonetheless. A typical sequence stored in memory might be eye-eye-nose-mouth etc and if we replay that sequence and encounter those facial elements in that order then we know we are looking at a perfectly normal face. Replay the sequence and get eye-ear-nose-mouth and we are instantly aware that the face we are seeing is very far from normal indeed. Prediction and surprise allow us to spot inconsistencies in the world around us, to differentiate between normal and off-normal and most importantly to help us identify errors.


If it’s equally probable that any one sequence of patterns could follow any other then there is no need for us to be able to make predictions and there would never be any surprises. The world is not like that however as sequences of patterns tend to follow a chain of cause and effect with one sequence of patterns naturally leading into the next. Drop an egg and you will predict that it’ll break when it hits the floor because that’s what eggs usually do when we drop them. What we didn’t predict however was that we were actually going to drop the egg in the first place. We probably expected to get the egg out of the box, carry it across the kitchen and put it in the pan, not get it out of the box, carry it over to the pan and drop it before we got there. We clearly made some sort of error in handling the egg which allowed it to fall, but because we did not predict this mishandling we are instantly surprised when the egg slips from our grasp.


If we fail to accurately predict the subsequent sequence of patterns from the current sequence of patterns then we become surprised by it and that is why prediction and surprise plays such a crucial role in road accident causation.


Prediction failures on the road.


As we ride along our memory of similar situations we have encountered before is allowing us to constantly make predictions as to what the next sequence is going to be. The car we are following puts its indicator on as it approaches a side road and we predict that the car is going to eventually slow down and actually turn into the road. Instead the car slows rapidly and turns into a driveway before the side turning so our prediction as to which turning they were going to use has clearly been in error and we get a nice big surprise as a result. Our friend who was riding belong behind us had noticed that the car driver was looking at the houses as he drove past them as if he was trying to spot a particular house number. When the indicator goes on your friend makes a prediction that rather than turn into the upcoming side road the car is going to turn into a driveway instead. Your friend is not in the least surprised when events turn out the way he had predicted them yet there you are with your heart pounding trying to brake or swerve to avoid the rapidly slowing car. Two riders facing the exact same sequence of patterns yet only one of them is surprised at how things actually turned out.


Riders are receiving a constant stream of sequences of patterns which they are using to make predictions and if their prediction is correct then they carry on as before, but if their prediction is incorrect then they automatically get a surprise. The rider that experiences fewer surprises therefore has made better predictions than the rider that experiences a lot of surprises and this is the critical link that underpins the no surprise no accident theory.




The surprise is the only common occurrence in each and every accident no matter what other variables were in play in the lead up to it. There are five common motorcycle accident types and all of them have a failure to correctly predict future events at their very heart. A rider is surprised when a corner tightens unexpectedly so somehow they have failed to predict the actual severity of the corner. A rider is surprised when a car pulls out in front of them so once again they have failed to predict exactly what the car was going to do as they approached it. When viewed from the perspective of prediction failures and surprises all the different types of accident are much easier to understand and learn from because the accident can be fully reconstructed from the point of view of the rider involved. Whatever the action of the other road user or the layout of the road environment it is at the point the rider got surprised that reveals exactly how their prediction of future events actually failed.




The above is only the very broadest overview of the functions of the human brain and how it makes predictions which generate surprises when those predictions fail. It is sufficient of an overview however to confirm that no surprise no accident should be the fundamental currency of road safety education and engineering. With no surprise no accident forming a substantial framework for all further investigations and interventions rapid strides can be made in helping riders to become better predictors and thus reduce the number of accidents and incidents that they suffer from.

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