A question about skid marks

Here is a question I received and answered on the now-defunct website AllExperts.com:

Are skid marks darkest at the end or beginning? And can you determine the tread from the tread marks? My daughter was in an accident and the cop cited her even though from his pictures it looks like the skid marks are in the opposite direction, and she never even applied her breaks because her car died on impact. If they are the darkest at the end that would prove they are not hers, Besides the fact they curve the opposite direction that her vehicle traveled. I asked about the tread marks because she has a very unique tire tread and blowing up the photos show they don’t match her tread.

This is a complex issue and I am not a professional forensic accident investigator, although I do have a working knowledge of the physics of car crashes.  There are actually three different types of skid marks: acceleration, braking and yaw.  Acceleration marks would be darkest at the beginning, where the car was stopped, because the friction eases as the tires transmit more of the power from the engine under speed.  Braking marks would be darkest at the end where the friction forces built to their strongest point (when the car either stopped or the brakes were released).  Yaw marks are the ones a tire makes when the car is skidding to the side.
 
Police responding to a crash scene have varying levels of training in forensic reconstruction.  The photos you provided are without context – there are no vehicles present in the scene.  From the photos only, there is no way to discern what vehicle made those particular marks, or even if they were made during your daughter’s crash.  The officer likely made his assessment of fault based upon the final stopped position of both vehicles and interviews with drivers and witnesses, if any – he may not have even examined the skid marks.
 
On police procedural shows like “CSI”, investigators often make use of tire tread databases.  In reality, I have no idea how complete these databases may be or what police departments may be making use of them.  The photos you provided here lack enough detail to make any accurate comparisons, but accident investigators on the scene would have taken enough photographic evidence to at least make such a comparison a possibility.
 
If you feel that your daughter has been accused wrongly, your best option would be to find a lawyer in your area familiar with traffic law.  The lawyer can review documentation from the accident investigation and recommend a course of action for your family.
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