Critical mass in evidence and the mistakes “accident investigators” make.

Critical mass: It’s not just about mass at all. In the context of the evidence needed to defend yourself or to win a legal battle, critical mass is the minimum amount of information needed to support your version, your claim or your innocence. After a road traffic collision, unless the evidence is so overwhelmingly stacked against you that you need to settle or plead guilty, the outcome of the trial sways heavily in favor of the party with the best information. But how much evidence should you collect to reach this “critical mass”?

In this article I aim to illustrate that critical mass when it comes to evidence – is more about quality than quantity. A favorite saying among litigators is that the devil is in the detail. They also say never ask a question that you do not know the answer to Very early in my career as a Forensic Road Traffic Collision Reconstructionist I determined and as I have proven countless times since critical mass is reached only when both the quantity and quality of a collision investigation is adequate. And quality can affect the quantity in more ways than I can count and for this reason, accuracy is vital. Nowhere more so than after metal has met metal, blood has flown, and spills have soiled the earth.

In this article, we will address the concept of critical mass as it relates to the collection of evidence at or after road traffic collisions. We will explore when critical mass is reached and what is the least amount of evidence you need to gather in preparation for possible litigation or trial. We will help you see how much you need to know in order to reach critical mass in terms of evidence. And more importantly what kinds of mistakes “accident investigators” make that lead to the dismemberment of their efforts to contribute as they aim to. The mistakes that force their contribution below the “critical mass” limit.

When it comes to the investigation of accidents or collisions and incidents, there are numerous issues at play. The reason why the “accident investigators” in the heading to this article is in inverted commas is because there are far too many people doing “accident investigations” but too few who possess the skill or experience to actually do so to the required level of competence. While incidents are not dissimilar to collisions, this is the one that results in the greatest losses and the most liabilities or risks. We will consider road traffic collisions, but other incidents are subject to the same logic and consideration.

Road Traffic Collision Investigation is a truly multi-disciplinary field of interest. Taking a couple of photos of your damages and that terrible spill – and a dead body or two, if you’re “lucky” – is hardly where skill and an experience qualification are needed. These days anyone with a cell phone can take photos or buy a cheap camera to do so and call their effort an “accident investigation.” But is this enough? Will you reach “critical mass” this way?

Let’s be clear – insurance loss adjusters or assessors are not actual “accident investigators” either. Their interest is quantum – the value of the loss. They are typically familiar with the cost of parts and labor related to the replacement of a lost item, repairs of damages or compensation for loss. The moment they start expressing opinions about how things happen or happened, they expose themselves to a host of challenges. If they are never required to go to court, never expected, asked or subpoenaed to testify and are never going to represent themselves or their findings, no harm no foul. But the world is not the simple, regrettably.

Average police officers, traffic officers and METRO Police officers that are tasked with the responsibility of “taking a scene” are technically “accident investigators” as well but their job is typically pre-defined: Detect a crime, identify the parties (or objects) involved, show how and where they were found. That’s it, as far as “accident investigation” goes nothing more, nothing less. Their work will typically yield an accident report, a photo album, and a sketch. Their work is typically completed at-scene or very shortly thereafter and then they move on to the next case when they are done or until they are called to testify. When they start to express opinions, they face the same challenges as assessors – they might move outside of their primary areas of expertise. Then the problems start: often, for you.

But what are those problems? How can or does it affect your collision, your claim, your criminal liability? In order for us to address this, we need to start at the end: at the judgment in a civil or criminal matter. Remember – there could be a claim against you, you could be claiming against someone else or you could be facing criminal charges.  Even the criminal charges against your driver can expose you to risk – but more about that later.

In addressing this, we will ignore confessions and admissions of guilt. Those are beyond the need for discussion. We will address the issues that require judgment in a matter where a suspect either pleads not guilty or where there is a dispute regarding liabilities and where a trial runs to a conclusion – those cases where the outcome must be determined by a magistrate or judge.

When judgment is made, a number of issues are considered. Firstly – and most importantly – the versions are considered. Many don’t realize this but as influence goes, the version of witnesses carries the most value. They were there. People do lie, but this is what cross-examination is for – to test their versions. At the end of the day, the court believes what people can testify they saw for themselves. 

So, if there are witnesses, they must be found, and they must be called to testify.

This is the first mistake accident investigators make – they let witnesses “getaway.” They only take a name and phone number. No address, no e-mail, no alternative numbers, no ID numbers and not even their vehicle details. Part of the IBF 124-point investigation protocol includes the at-scene photography of all vehicles present. This makes tracing witnesses a lot easier, later. Without witnesses that were actually there, critical mass cannot be reached.

Next, the court will consider any physical evidence. There is a term called res ipsa loquitur. It means “the facts speak for themselves”. But people tend to confuse this term with the value of conclusion. Facts are things that are beyond argument. 

They are the things that are available before the court and plain to see. Like a CCTV video of a car hitting a parked truck in broad daylight. If the evidence is so good that res ipsa loquitur can be applied, the court can render a finding based on them alone. But this is seldom the case in road traffic collisions.


Accident investigators make the mistake of believing that res ipsa loquitur is the same as “obviously”. It is not. Just because you can “obviously see that the car was speeding” is a lay opinion in the absence of analysis, proof, and conclusion. At scenes, investigators make the mistake of forming an opinion based on their deductive reasoning – they think they know what happened and who is at fault because it is “so obvious”. What makes the 124-point IBF so effective is that it FORCES us to do the same investigation at all scenes – without considering what we see or of what is “obvious”. If an investigator only focuses on what is obvious, vital elements of evidence can be excluded. Things like checking lamps for states of incandescence or tire conditions on dry road collisions. Both affect critical mass. Without “all the evidence”, critical mass cannot be reached because the elements that are relevant might only become clear in court one day, years later.

Lastly – there is expert testimony. The first issue is with the determination and acceptance of an expert witness. No person can declare himself an “expert witness”. He or she can be called as an expert witness, but ultimately the court will finally rule as to whether this status has been achieved, or not. In simple terms and without reference to specific cases and judgments, an expert is basically any person who holds any qualification, skills, knowledge or experience that places him or her in a position to assist the court with the understanding technical or complex concepts that extend beyond the scope or skill of the general person. This excludes the things you can “obviously see” and the conclusions that you can draw “because I can look for myself”.

Telling the court that you arrived, saw the cars and photographed where you found them, what damages you saw and who was involved is not expert evidence. That is something anyone could have seen, found or photographed. The moment the “investigator” starts saying “and it looks like…” or “and therefore it means that”, he or she is starting to express and opinion. In order to do so, he or she has to satisfy the court that they possess those unique qualifications, skills or experience that goes beyond that of the general public.

If a normal witness starts to testify about how they think things happened or about why they think it happened – they are expressing an opinion and there will be an objection. General witnesses to the fact can only testify to facts. They can only say what they saw and did. Accident investigators make the mistake of expressing an opinion in reports or in testimony. The moment those objections come; they start defending themselves. This is never received well in court and could result in all their evidence being excluded on the basis that they are unreliable or argumentative.

An expert witness, on the other hand, can express an opinion. This is what they are there to do: to assist the court in understanding concepts or that the general population would not understand or grasp without clarification. The expert witness is there to help the court – nothing more, nothing less. He or she does not “represent” a client, they do not “defend” and they do not “prosecute”. They are not there to assign blame, guilt or innocence and they are not there to ensure any particular outcome. This is another mistake accident investigators make: they invest in the case – often emotionally. This can lead to their objectivity being called into question and their testimony being disregarded on account of bias.

Now that we’ve addressed some of the issues that influence and affect judgment, let’s talk about the testimony. Going to a scene and taking photographs or even measurements is hardly where it all starts and ends. People forget that – where serious cases are concerned – cases will often end up in court. When it does, you might be called to testify. Almost all accident investigators – private and government – make the mistake of focusing only on their task at the scene and completely disregarding the likely lines of questioning they might face, as a result of their actions.

When you testify in court, there are a number of things you need to be very aware of. If you fail as a credible witness, critical mass is declared moot because all your evidence, your opinion, and your value as investigator can be discarded, based on how you perform as a witness. This means that the quality of your work can be completely compromised by the quality of your actions. The actions of the investigator, in the absence of credibility, can be the reason for critical mass not being reached.

A common mistake of accident investigators is that they have no legal experience, training or qualification. The method of evidence collection, your right to do so, the methods used and the protocols you follow at a crash/crime scene can reflect very negatively on your testimony. As an example, if you started photographing a scene without the following protocol, without declaring your presence, reporting at the Joint Operations Command (JOC) or seeking permission to enter a crime scene, your presence can be questioned. My DIY Accident Investigation Manual, 124-point Investigation Protocol, and our training specifically cover this. Accident investigators make the mistake of not knowing how to gain legal access to crash/crime scenes. If this becomes apparent in testimony – during cross-examination – it might result in embarrassment and emotional outbursts. What would your answer be if you were called to testify and you were asked: “Who gave you permission to take these photographs?” What if no one did? What if you just entered the scene and started taking happy-snappies? Accident investigators make the mistake of not knowing what rules, laws or protocols allow them access to crash/crime scenes and it places them in very uncomfortable positions in court.

Another common mistake made by accident investigators is that they refer to hearsay evidence. In most cases – especially criminal – hearsay evidence is not allowed. Investigators make the mistake of asking people to “tell them what happened” and then use those versions as a starting point for their investigation, report and testimony. Since hearsay evidence is not allowed, all evidence that follows would not be allowed. If an accident investigator’s report is based on (or only based on) the word of other people, the information that follows will not be allowed into evidence. Then critical mass will not be reached either.

Another common mistake accident investigators make is that they do not record everything they see, hear, experience and see. They take their photos and leave. They put them in a report and write that “these are the facts”. In this case, they are often cross-examined on source and method. A common question is: “How did you determine this?” The unskilled, untrained or inexperienced accident investigator will not realize that this is a trap that he could step into. If he answers along the lines of “someone told me”, he ventures into a hearsay territory and his evidence will become weak. If he expresses any opinion such as “I determined that” or “I concluded that”, he might not be allowed to continue on the grounds that he is not an expert witness. Our training, the 124-Point IBF Protocol and my DIY Accident Investigation book covers the very methods used to ensure that all evidence is collected correctly, everything you experience is recorded correctly and that you are prepared to testify to your reports. If you cannot disclose or confirm the source of your information or opinion, you will not have reached critical mass either.

Next, we will consider the actual reports compiled by accident investigators and the actual mistakes they make. The first mistake they make comes in the form of the inclusion or compilation of statements. Inexperienced, unskilled or untrained accident investigators love including the “versions” of drivers in their reports. This sounds logical. Surely, you must include what the driver said happened, in a road traffic collision? Maybe, but not always.

When someone is involved in a collision with a company vehicle, the company often wants a version in a report. This makes them happy since they can then dismiss the driver if he was found to be grossly negligent or if he acted illegally. Accident investigators are often appointed to do investigations for this purpose and are even asked to express opinions about fault. These often “slip through the cracks” as labor disputes are not subject to the same rules of evidence and scrutiny as court and criminal matters. Companies are happy because they can get rid of that “problem driver” and the accident investigator walks around very proud that “his investigation, report, and testimony resulted in a favorable result for his client”. This is a mistake.

See – in criminal matters and in civil matters, there is a sequence of interaction. In very short terms, one party issue a summons, the other party shows intent to defend, they exchange heads of argument and then…There is a discovery process or the criminal investigation. This is where either party in a civil matter can request the disclosure of any/all records deemed relevant or that the other might intend to use in or during the trial. This means they can ask for all minutes, reports, documents or recordings used during the hearing of that driver you were so happy to get rid of. The police officer in a criminal matter can get a court order for the same and use it against the driver.

In both cases, it can also be used against the very client the accident investigator served. The problem comes with negligence or vicarious liability. If the owner of the vehicle is found to have been negligent in any regard with reference to (say) vehicle maintenance, criminal charges can be extended to include him or her. In the civil context, the more “wrong” your driver is, the greater your vicarious liability becomes! Vicarious liability is the degree to which the owner (or company) is liable for the errors and actions of an employee. This means that the accident investigation report and all the statements therein can be used against you or the driver in a civil or criminal matter. Suddenly, the “right to remain silent” is not achievable and critical mass is not reached.

But this is not where it all ends! Accident investigators also make gross errors at scenes, during their investigation. One of the most prevalent mistakes made by accident investigators – and this now includes police and traffic investigators as well as expert witnesses – is poor measurement and the compilation of inaccurate sketches. In 15 years in this industry and after hundreds of trials. I have never once ever seen a properly compiled scale scene drawing or sketch. I have not seen a properly compiled scale scene drawing, including all relevant elements and I, have not seen anyone use either the coordinate or the triangulation method of measurement properly. I’ve seen professors of mathematics draw scale drawings that completely do not represent the actual scene at all. I have seen so-called experts use Laser Total Stations to measure crash scenes and compile computer-generated drawings and still leave out a lane completely from their drawings. This is not only the most common mistake accident investigators make but rather the most unlikely task they are going to perform properly and effectively. But this is not because it is highly advance, highly complex or impossible at all. In our training students are taught to draw accurate scene scale drawings in a day and more than 95% get it right the first time around. The problem might be a lack of interest or poor training, but the results are the same; if the positions of vehicles and the general scene cannot be properly determined or measured, critical mass cannot be reached.

I used aerial photography and scaled images in a permanent 3D environment to produce highly accurate scale scene drawings. Not only does an aerial photograph include all elements small and large – there is also nothing that is present that cannot be seen, represented and considered exactly where they are. If an accident investigator intends to testify, and if he or she hopes to reach critical mass, the accuracy of his or her at-scene measurements is vital. If bends in roads, road widths, vehicle positions or the length of skid marks are not properly measured, analysis becomes impossible. Critical mass is never reached, to start with.

The last mistake accident investigators and even experts make are to learn through example only. We often see in trials that witnesses express opinions they were taught to express. Things like ‘it is commonly known that the perception reaction time of a person can be between 1.5 and 2.5 seconds” is often heard and even used in the analysis. The mistake here is that investigators often refer to this because they were “told so in training” or because they read it somewhere. The same goes for the methods used for speed analysis, conclusions regarding lamp incandescence and opinions regarding more complex issues like crush or the old favorite: Principle Direction of Force (PDOF). Before accident investigators refer to the opinions or references of others (as a matter of fact), they almost always fail to explore all research or aspects relating to those “facts”.

As an example, the research by Greene, Lerner, et al is very regularly used by reconstruction experts – especially those from the engineering fraternity. This is all good until you actually go and get a copy of their research and read that the research cannot be used for road traffic collision analysis and that the research was done for traffic light timing design. Accident investigators like to refer to values of between 1.5 and 2.5 seconds but this is incomplete disagreement with later research done by Joseph Badger, Jeff Muttart and many others. So the take-away here is that accident investigators should do their own research and stay up to date with the latest research.  As an example, if accident investigators bothered o actually acquire a copy of the research paper, they would see that one of the opening paragraphs include the following statement: The Human Factors Guidelines for Road Systems is not a guide to crash investigation or a comprehensive reference for safety diagnosis. So, you would agree that reference to this work would be quite a serious oversight. Yet accident investigators are still taught to use this reference – even today.

When accident investigators are too lazy to do their own further research and simply quote what they have been told or what they have read in one incomplete reference, they stand the risk of being discredited at worst or of being forced to reconsider better references and to re-do their analysis or amend their opinion at best – often to the detriment of their original finding. If a witness is forced to reconsider his position and in so doing discredits his own original version, finding or opinion, critical mass can definitely not be reached.

While all aspects are not covered here, at least the following is needed for critical mass to be reached in terms of a collision investigation, report or the testimony that stems from it:

  1. The investigator must gather all evidence – not only the evidence he/she thinks is relevant.
  2. The evidence must be collected in the correct way, legally and completely.
  3. The investigator must know and understand the process of law in order for the investigation to be effective.
  4. The investigator must record, document and retain all records, information and evidence found, observed or collected at the collision scene.
  5. The investigator must know and understand the experience he or she will have in court while testifying and align his at-scene efforts thereto.
  6. The investigator must know the rules of evidence, the rules of testimony and the pitfalls he or she could face in court. 
  7. The investigator must fully understand his/her role, contribution, mandate, and limitations when it comes to compiling a report and beyond – into a trial.
  8. The investigator must be familiar with court procedure, grounds for objection, the limits of his/her testimony can have on the outcome of the trial.
  9. The investigator must be objective, clinical, professional and capable as a witness – whether expert or not.
  10. The investigator must know and understand the difference between opinion testimony, witness testimony, expert testimony and lay testimony and where he/she fits into the trial process.

If at least this is not achieved, critical mass cannot be reached. If critical mass cannot be reached, the accident investigator could – through his/her own inexperience, lack of skill or ignorance – end up effectively testifying against you, tipping critical mass in favor of the other side or of your guilt. Choosing an accident investigator and doing a proper accident investigation goes hand in hand. These are not issues to be considered lightly.

When you consider these mistakes, that are all typically and regularly made by accident investigators, you should be asking yourself if “Jim from the workshop” is still the right man for the job, whether you believe he should receive proper training or whether you should invest in some books for him to read to further familiarize himself with the most common mistakes he could be making right now, at your expense. Or perhaps you should be considering a longer-term relationship with an external expert. Someone who can and does know how to investigate collision properly, the pitfalls of the law, the proper way to testify and when to give you advice that will help you reach critical mass.

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