The Value of Skid Marks for Auto Accident Cases

Not only do tires play a vital role in the performance of your car or truck, but a lot of information can be garnered about what happened before, during, and after a crash. Tire marks will be explored by us and, generally, what those marks tell us.

First let us discuss where the marks come from. Skid marks are created by the extreme thermal relationship of a tire against the roadway surface during extreme stresses put on the tire, a simpler way to say this is, a tire will "mark" when it nears, or exceeds, the limits of its relationship with the roadway. These marks occur because the oils in the roadway and/or the tire(s) are brought to the surface and "melted or burnt" into the roadway. If a tire is heated enough since the surface of the tire will have changed, it'll be obvious, it is going to have a spot and obvious abrasions.

Kinds of Skid Marks.

There are three specific kinds of marks we will talk about, these are the most typical four wheeled car and light duty truck marks. (Other vehicles, such as motorcycles, have different specific marks).

Light to Dark or Dark to Light

All marks can be placed into two categories when referencing the management of the vehicle which made them. Light to dark marks (in the direction the vehicle was traveling) support a vehicle making the marks through some kind of deceleration (extra points if you wanted to read "negative acceleration"). Dark to light marks (again, in the direction the vehicle was traveling) support a vehicle making the marks through some form of acceleration, usually excessive wheel spin.

Darker from the Middle, Darker on the Outsides, or Uniform

Marks that are darker in the center indicate a tire that's overinflated, conversely marks that are darker on the outside edges indicate a tire which is underinflated. Indicate a tire.

ABS Versus Regular Marks

ABS (Anti-lock Brake System) marks are lighter than conventional marks and have more tire tread definition in them, Non-ABS marks rarely have tread definition inside them. ABS marks are also shorter when compared to non ABS marks from a vehicle traveling in precisely the speed.

What else can skid marks tell us?

As you have already found skid marks may tell us about the tires inflation, ABS or non-ABS braking, and direction of travel. Marks can also tell us something when and in which the decision to brake occurred. This is the most under-utilized and under explored aspect even more so in speed crashes. Some basic calculations can be made, using a variety of aspects of the skid marks, to determine where the driver made the decision.

Why is this so important? Consider the following illustration.

This drawing is a timeless teaching example used to demonstrate the value of skid marks. Consider this situation, the blue car says he had the green light and was hit at the intersection. The car says so that that he braked hard he also had the light and saw the car. There isn't any other evidence or witnesses.

Now the student would be asked to calculate the position of the cars once the decision to brake was created using the beginning of the skid marks, ultimately this would place the vehicles in the place labeled 1.

Now the apparent problem with the red car's situation now that we have used the skid marks to ascertain where he determined to brake, a construction blocks his view of the blue car (position 1 for both vehicles). This begs the question as to why did he decide then to brake? The answer, the light was red for the red car and the driver was braking for traffic lighting, not the blue car making the red car culpable in this situation as the physical evidence affirms the "at fault" party.

Another valuable piece of advice is that rubber is biodegradable and there are naturally occurring nitrogen based bacteria that "eat" rubber. These bacteria are competitive and will eat rubber in most environments, therefore if you're trying to determine causality and the "at fault" party, it is in your best interest to take pictures of the roadway whenever possible. Skid marks are gone in a brief amount of time.

Skid marks are a valuable item of evidence and a great tool for determining many facets in a collision; it is extremely important none of them are overlooked or underestimated.

The scope of our information is limited to chiropractic and spinal injuries and conditions. To discuss options on the subject matter, please feel free to ask Dr. Jimenez or contact us at 915-850-0900 .