Tire marks left in the roadway can help reconstruct many aspects of a traffic accident. A private investigator working up a traffic accident reconstruction can analyze tire marks, skid marks, debris fields and witnesses, to develop a picture of what happened, and in what order.
Tire marks, in particular, can tell the private investigator about what a driver did, or attempted to do, before and after a collision. A point of impact can be determined. Speeds of deceleration before impact, swerving and braking activity can also sometimes be derived from tire marks.
So how can an experienced investigator use the tire marks to tell what happened?
Tire marks can be of several types. To list a few:
- Scuffs – made by a rotating vehicle, or a flat tire
- Pre-skid shadow marks – can show vehicle speed at beginning of skid
- Yaw marks – made by a tire that is rotating and sliding sideways
- Skids – made by a locked wheel, indicating sudden braking
- Erasure – caused by a sliding locked tire, erasing loose material from the road
- Squeegee – similar to erasure, but on a wet roadway
- Smear – caused when a tire is hot enough to smear the rubber; usually seen on concrete roadway
- Gap skids – caused by pumping brakes, or anti-lock brakes
- Acceleration marks – “laying rubber” by fast acceleration that spins the wheels
- Scrub marks – caused when a vehicle is redirected by impact; useful in determining point of impact
As can be seen by this list, good photographs of the scene of an accident, taken immediately thereafter, are CRUCIAL. With most everyone having a mobile telephone nowadays, we see many cases where great photos were taken right after the accident.
But INTERPRETING the photographs is where a private investigator’s skill and experience come into play. Tire mark interpretation involves three factors:
- Vehicle Speed (determined by the marks, as of the start of a skid)
- Drag factor – derived from the type of roadway (asphalt, concrete, dirt, gravel)
- Braking efficiency (expressed as a percent)
Using these three factors, an experienced private investigator can tell which of the many speed calculations to use. Say a vehicle left a 150-foot tire mark on asphalt roadway. If the tires left a yaw mark, that calculation will yield a speed of 48 mph. If the tires left straight skid marks, the calculation will yield a speed of 56 mph. An eight-mph difference might not mean much, unless the posted speed limit is 45 mph. Thus, this kind of calculation can be CRUCIAL to determining which driver(s) caused the accident.
Understanding and identifying tire marks is an essential part in accident investigations. You need an experienced private investigator to review all the evidence in your case.
- Determining Vehicle Speeds from Skid Marks: http://www.hhs.iup.edu/CJANICAK/SAFE541CJ/Skid%20Mark%20Evidence.pdf
- Ohio PD: http://www.ohiopd.com/skidmarks.php
- American Prosecutors Research Institute: “Crash Reconstruction Basics for Prosecutors”: http://www.ndaa.org/pdf/crash_reconstruction_basics.pdf