Forensic Engineers and Consultants

Blog Posts by: Al Duncan

Author Al Duncan


Expertise Includes:

  • Vehicle Collision Reconstruction
  • Crash Data Retrieval
  • Forensic Mapping Technology
  • Motorcycle Collision Reconstruction
Green Hotrod with Fancy Rims and Huge Tires

The Pressure to Keep Rolling – Part 1


Over my years of law enforcement, crash investigation, and collision reconstruction I have come to become more and more particular about my tires. I have watched people purchase tires from these “Used Tire Stores” and when I buy my tires I can understand why; quality tires are expensive. The question of how old is that tire and how was it serviced before it ended up for sale is a huge concern. I have watched people put their compact spare tire (commonly called the donut spare) on their vehicle and ride on it for weeks even traveling down the interstate a speeds way above the recommended rating on the tire. I have had a tire dealer (that sold new tires) try to sell tires and rims that are not safe combinations because they go against the vehicle and tire design. Needless to say, much to their dislike, I wouldn’t cooperate with them because it didn’t make them money; however, they did not end up in civil litigation either.

Used Tire Sign

I have seen people do things to be trendy like lifting or lowering a vehicle way beyond the vehicle manufacturer’s intent. People lift and lower their vehicles by changing the size of their tire or wheels (this brings in a whole new concern if they change the rims because they too are rated and designed for specific applications) without consideration of the vehicle’s relationship to its tire design. Sometimes the tires rub, causing wear and damage to the tires, which becomes a safety issue.  Each time you go up or down in the height of the tire you are changing the revolution speed of the tire. This in turn changes such things as the accuracy of the speedometer. The change in speed being displayed compared to actual speed may only be 1 or 2 mph difference at 5 or 10 mph, but 15 to 20 mph off at 55 or 60 mph.

Green Hotrod with Fancy Rims and Huge Tires

With the complicated safety systems communicating with each other within a modern vehicle’s computer system and making decisions in milliseconds (especially things like airbags, traction control, and anti-lock brakes), having erroneous data generated by the use of improper tires yields not only a concern for a speeding ticket but to a vehicle’s improper response to conditions of a crash. If there is a need to change tire sizes, find a trusted and reputable tire company to walk you through the change so that you have the least amount of repercussions from the switch.

In part 2 of this blog we will go over where to find the proper tire and loading information for your vehicle, and what these values mean, to ensure you are getting the maximum safe performance from your tires.

3D Collision Impact Angle

Why investigators should have “Scaled Diagrams” of scenes?


When it comes to diagramming a crash scene, there are several methods to complete the task. Forensic Mapping, (locating, positioning, and documenting the evidence of a collision scene to scale) is essential to having the answers to the questions “Who, What, Where, When, and Why”. Photographs do a great job showing what the investigators saw post collision; yet they lack scale and the ability to describe pre-collision movement. Having a computer aided diagram (CAD) of the collision scene goes much further than the pictures can; here is why.

basic intersectionA scale diagram gives the full overview of a collision scene from either a 2D or 3D point of view. Being able to see how things lined up, how they came together and how they parted helps explain the events within a crash. When a scene can be viewed from top down or any angle, that helps relay the facts. The investigator, judge, or jury will get Read More

Right Turns Only main photo

Right Turn Only



In my 25 years of investigating collisions and traffic related incidents, one thing I have noticed repeatedly is that right turns are considerably better than lefts. I know it is obvious and sometimes seems a little petty; however, when it comes to the safety of your family, it is a big deal. Since I am currently in the process of teaching my second child how to drive, I am harping on vehicle safety a lot and this is one of the many practices I teach. I have instilled in my children (and my wife has picked up on it as well) that they should always plan out their route and, in doing so, make right turns instead of lefts whenever possible. The “Right Turn Only” practice will make your travels safer.

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Are 10 Minutes Worth the Risk?


Before retiring as a S.C. State Trooper, and to this day, people routinely ask me, “How fast can I go before I get a speeding ticket?” Let me start by saying one mile per hour over the speed limit can subject you to a speeding ticket. While different officers have different standards, it is easier to talk your way into a ticket than to talk your way out of one. So, much like the number of licks to get to the center of a Tootsie Roll Tootsie Pop, the world may never know an exact answer to how fast you can go over the posted limit without a citation. A better question is ‘What is the benefit of exceeding the posted limit?’ Read More


Piecing it Together…Traced Evidence


In the field of forensic investigations of traffic collisions, it can be repeated over and over that little things matter. It’s the details that align the facts to describe the event and answer the questions about the crash. Sometimes those details are simple, and they are often overlooked. The damage sustained by a vehicle involved in an accident tells a reconstructionist a lot. Your collision reconstruction could benefit from mapping the damage profiles of the involved vehicle(s) to assist in answering questions about the incident. Read More

Black box inside car

Event Data Recorders and Collision Investigation


Event Data Recorders (EDRs) were first introduced by General Motors (GM) in 1974.   That data was only available to GM; however, since 1994 more and more vehicle EDR’s have recorded data that can be gathered.  The data captured can be imaged and is being used by vehicle manufacturers, law enforcement officers, and collision reconstructionists to better understand what is happening in a collision.  In accident investigation, EDRs have the potential to provide independent measurements of crash data that would elsewise be estimated by Read More

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