In a previous blog post, I gave an overall introduction to the 9-Cell Collision Matrix as an investigative tool used in collision reconstruction. Now let’s focus in a little at each element.
They are called car wrecks, after all…so let’s start with a more comprehensive look at the vehicle component of the matrix. This review of the vehicle before, during, and after the collision will highlight a few important factors but is not meant to be all-inclusive. So, let’s get started!
If we started with the vehicle out of our choices of the human, the vehicle, and the environment, then perhaps we should begin an analysis of the vehicle at its foundation, of course I mean the tires. So, do tires fail and cause car crashes? You bet! Do tires fail as a result of a manufacturer defect and cause car crashes? Sometimes, but not very often. Tires fail and cause car crashes most often due to poor maintenance, and there are a lot of sub-categories that fall under this heading. Let’s look at a few.
The most overlooked, and easily preventable problem that rears its ugly head with tires is improper tire pressure. Both underinflation and overinflation causes issues, that left uncorrected, will eventually cause a tire failure. Our old friend heat ranks near the top of tire enemies and underinflation is its weapon of choice. Underinflation causes excess heat buildup and undue stress to the tread and sidewall area of the tire, eventually leading to a tire failure. How much air pressure is in that tire? Can you look at a tire and tell? Stop reading now and jump to the next paragraph if you don’t want to see the spoiler…short answer… No! In order to maintain the manufacturer recommended air pressure, the tires must be routinely checked and adjusted throughout the seasons of the year.
Moisture is another major player in the tire problem game. How was that tire puncture repaired, plug or patch? If it was a plug, you may find that moisture has seeped in around the plug and is now living inside the tire. Radial tires are comprised of steel belts for strength and support. If a repair plug has either been improperly applied, or over time has allowed moisture in, it is also allowing air in the structure of the tire causing oxidation. Over time the oxidation process will rust the steel belts, often causing a belt separation and tire failure.
When I was a Trooper with the South Carolina Highway Patrol, we were supplied with most things uniform related including shoes. All of these items were stored in a warehouse and given out as needed. Some of these items were needed less often than others and had been stored in the warehouse for some time… that included a pair of shoes that were once supplied to yours truly. After many miles, I decided to replace my old shoes before work with a “fresh” pair that I still had in the box. I laced them up, walked outside to sign on the radio in my patrol car, when I noticed my new shoes felt funny. When I looked back down the walkway, I saw the culprit… my new rubber soled patrol shoes were now moccasins! Why had the rubber soles come completely off my new shoes, shredded to bits, in a distance of 100 feet? Because they were old, and the rubber compound had degraded in the warehouse conditions. The same thing happens to tires, especially that old spare tire that is only needed when it’s needed. This can be and often has been a recipe for disaster. How old are your tires? Turns out it’s pretty easy to tell with the DOT number located on the tire sidewall. The DOT number will typically have a series of numbers and letters followed by a final four-digit code indicating the week and year it was manufactured. Typically, tires over 5 years old need to be replaced due to age.
Poor tire maintenance is a condition that predominantly affects the vehicle prior to the collision. How much air is in that tire? Better get a gauge and check! Next, let’s see what tire conditions reveal themselves during the collision.So, what’s going on with tires during the wreck? My tire blew out and caused me to wreck! Heard that one a few times, right? Often tires are not in their original inflated, properly beaded on the rim condition after a wreck. Does this mean that there was a tire failure, and the tire failure caused the crash… maybe, but I doubt it? Even if the tire blew out and caused the crash, more often than not, you’ll be looking at some level of improper tire maintenance.
Typically, what happens in most cases is the driver of the car exits the vehicle or sometime later after seeing the vehicle, sees that the tires are no longer attached to the rim, and declares that the tire blew out, causing the crash. In reality, the cause of the tire separation is that the vehicle rotates during the crash dynamics, often leaving the roadway and traveling across a grass / dirt surface. This rotation causes a loading force on the tires, ultimately causing the tires to debead, the rims to start furrowing the surface, and the vehicle to overturn. This condition is a fairly easy diagnosis in that there will almost always be a surface transfer into the tire bead / rim edge area, be that grass, dirt, pine straw, or the like.
What if we really did have a tire failure that caused the wreck… be that a manufacturer defect, improper mounting, improper maintenance, or you name it? That should reveal itself fairly obviously in most cases. Bear in mind we are talking a catastrophic tire failure here. A few things to look for at the scene would be a scalloped flat tire mark on the roadway, along with rim gouging of the road surface and corresponding rim damage on the vehicle. Take special note that this evidence will be prior to onset of the collision dynamics… evidence of a causative precursor if you will. We should also find and collect the tire carcass if there has been a separation. This will provide an invaluable amount of evidence as to the catalysts of the overall tire failure.
After the collision it’s really just a matter of a timely inspection of the tires. This ensures that the tires and possibly evidence of a tire failure have not been influenced by any outside force.
Was the tire sized to the appropriate OEM vehicle specifications? Were all four tires the same size? Did all four tires have equal air pressure? What about tread depth? Were the tires retreads? During the course of a collision reconstruction, it is worthwhile to take extra time to thoroughly inspect and document those tires… after all, they’re the only thing touching planet earth as the vehicle travels 80 mph down the interstate.
In the next blog we will take a good long look at a topic near and dear to my heart, the airbag control module… and no it’s not a black box! Well sometimes, but mostly silver!
Mark Turner, ACTAR #2368, is a vehicle collision reconstructionist with Warren. Prior to joining Warren, he worked for 25 years as a South Carolina Highway Patrol Trooper including 10 years as a Multi-Disciplinary Accident Investigation Team (M.A.I.T.) leader (corporal). Mark is accredited as a Traffic Accident Reconstructionist by The Accreditation Commission for Traffic Accident Reconstruction (ACTAR). He investigated in excess of 900 vehicle accidents and incidents as a trooper. Then, as a member of M.A.I.T. for 10 years, he was involved in over 1000 detailed investigations and collision reconstructions. Mark has testified multiple times in state courts and has been court qualified as an expert in accident investigation and collision reconstruction. Mark is a member of the South Carolina Association of Reconstruction Specialists (SCARS), the International Association of Accident Reconstruction Specialists (IAARS), and the National Association of Professional Accident Reconstructionist (NAPARS). He completed the Law Enforcement Basic Program at the South Carolina Criminal Justice Academy in Columbia, South Carolina.