Transportation and Vehicle Safety/skid marks and tread marks


skid marks
skid marks  

anouther view
anouther view  
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 dont 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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Michael Mercadante


Questions on traffic safety, safe performance and operation of a motor vehicle in traffic, about driving with special needs, learning/behavioral/developmental disabilities, understanding vehicle laws, understanding safety equipment on vehicles, defensive and precision driving techniques, driver education and instruction and driver exam preparation.


Owner and sole driving instructor for Modern Driver Institute. Eight years in traffic safety research on contracts for NHTSA, FMCSA, AAA, MDOT and PennDOT. More than 1,000 hours as a professional driving instructor. Licensed driving instructor in the state of PA. Certified Defensive Driving Instructor for the National Safety Council. Precision driving for Hollywood and independent films. Expertise in virtual-reality driving simulators and teaching students with developmental/intellectual disabilities, traumatic brain injuries and more.

member, Teen Safe Driving Coalition; member, PA Safe Kids coalition; service provider, PA Bureau of Autism Services; service provider, PA Office of Vocational Rehabilitation.

Perkasie News-Herald WonkaVision Magazine Philadelphia Zoo website Driver Training Services website Yahoo! Associated Content

Licensed driving instructor, PA Department of Education Certified Defensive Driving Instructor, National Safety Council B.A. in American History (cum laude), Temple University (earned 2007) M.S. in Psychology, specialization in Educational Psychology (2015) Ph.D in Psychology, specialization in Educational Psychology (expected 2019)

Awards and Honors
Scientific Paper of the Year (2003), Association for the Advancement of Automotive Medicine.

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