Let me start off by saying I’m generally skeptical of the benefits of an accident reconstructionist as an expert witness in most car accident cases.
Why? Generally, I think in most liability dispute cases, jurors feel like they have all the information to make the call. Jurors think they understand basic physics and who is telling the truth and rarely look for help from an accident reconstructionist. We had a young lawyer trying his first case against a big law firm in a liability dispute case. The defendants hired one of the best accident reconstructionists in Maryland. Our client barely spoke English. We did not bring an expert. But we won because the jury heard the facts and believed our client.
We hire accident reconstructionists in the vast majority of our serious injury and wrongful death cases. One reason is that you don’t know whether you need an expert until you have gotten to the courthouse steps. But, even more importantly, they can help you gather and sort through the evidence to put you in the best position to win your case and maximize the value of your claim.
What is Accident Reconstruction?
Accident reconstruction is the scientific process of analyzing and making conclusions about the cause of an accident. It is based on the use of technology, physics, and mathematics to investigate how a crash happened. It is a technique commonly used by police departments and prosecutors to figure out who is at fault for a crash. But accident reconstructionists can also be hired to serve as investigators and expert witnesses in private car accident investigations.
An accident reconstructionist is a detective of sorts. They are tasked with determining what happened before, during, and after a collision. And they accomplish this by gathering evidence from the scene of the accident that allows them to make scientific conclusions. These investigations are intensive, encompassing more than just a cursory glance at the vehicles in question.
Accident reconstruction requires consideration of multiple factors such as: the point of impact; the vehicles’ final resting position; skid marks, gouge marks, and other identifiers. These data points are then inputted into computer software, which will often create a computer-rendered recreation of the crash. From this, an accident reconstructionist can make inferences and conclusions about the cause of an accident.
Deterniming How Fast a Vehicle Was Going
When a car accident occurs, often the speed of the vehicles is relvant to who is responsible. To make this determination, you look at things the force of impact, how long the collision lasted, and how much the vehicles accelerated during the collision.
To understand how to do this takes you back to high school math and physics. There are four main physical parameters: length, time, force, and mass. Length is measured in inches, feet, or meters, while time is measured in seconds. Force is measured in pounds or Newtons, and mass is measured in slugs or kilograms. It’s important to note that mass and weight are often used interchangeably, but they are not the same thing. The true relationship between mass and weight is expressed by the equation w = mg, where w is weight, m is mass, and g is the gravitational constant, which is equal to about 32.2 ft/s2.
To determine how fast a vehicle was going before a collision, the starting point is measuring the length of skid marks left by the tires. Skid marks happen when a car’s tires lock up and slide on the road surface. You measure the length of skid marks from each tire and calculate the average distance by adding the lengths together and dividing by four. The general velocity equation is: vf2 = vi2 + 2ad. (To translate: vi is the initial velocity in fps, a is acceleration (friction coefficient times g) in ft/s2, and d is the length of the skid/tire mark.)
But there is more to consider. The damage sustained is also relevant. Car manufacturers and regulators provide information on how fast a car’s bumpers, crumple zones, and side panels will fail, which helps determine the speed of the collision.
The drag factor, or the coefficient of friction, is another important consideration when calculating speed. Different road materials have different drag factors, and the presence of ice can further impact it. Braking efficiency is also crucial, with vehicles having different braking efficiencies based on whether they have rear-wheel, front-wheel, or four- or all-wheel drive.
Finally, the road’s grade, superelevation, and radius of a curve are also a potential part of the calculation, along with the weight of each vehicle involved in the collision.
- How to calculate distance per second
- More advanced math calculations to estimate speed
Why Would I Need An Accident Reconstructionist?
Car accidents are usually isolated events that happen within a frame of a few seconds. It is difficult for a witness to give an accurate statement on what happens in that time frame. For example, you know when you are watching a Ravens game and you see a close play live? It is impossible to tell exactly what happened because everything happened so quickly. That is basically what happens at accident scenes. So think of an accident reconstruction investigation as the slow-motion replay. (Actually, it is not that at all. But you get the idea.)
With that in mind, you only need a car accident reconstructionist when liability is at issue in a car accident case. The vast majority of car accidents are cut and dry when it comes to liability. X turned in front of Y. Y rear-end X because he was on his cell phone. In these cases, you do not need an accident reconstructionist to give you a slow-mo replay, because it is obvious who is at fault. To continue with the football analogy, you do not really see a lot of slow-mo replays on 3 yard runs up the middle. The spectators get the point, just from watching live.
However, liability is not always clear. Meaning parties will have to rely on the testimony of witnesses to support their claim that the other party was at fault. Witness testimony is shaky though. To illustrate, I implore you to recount what you had for lunch three days ago. Just imagine asking a total stranger to remember what they saw at an accident scene one year ago. With that being the case, hiring an accident reconstructionist inserts some objectivity into the process. Accident reconstruction relies on data points, not memory. Plus, an accident reconstructionist can testify as an expert witness, which allows them to give an opinion as to why the accident happened. So relying on a reconstructionist can help supplement and solidify eyewitness testimony.
I certainly do not think you need an accident reconstructionist in every case. But there are some cases where you would be very foolish to proceed without one.
More Required Reading
- How to prove fault in a car accident case
- How to admit property damage photos into evidence
- Outline of direct examination of an accident reconstructionist
- Sample deposition of an accident reconstructionist