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Forensics of Acceleration Skid Marks Part 2

Because of constraints in teaching this level of science in a "tele-learning" format, I must use extreme examples. Subtle important differentiations will remain assumed. Thus, in a spectacular crash is an excellent example of an Acceleration Skid. Here the force of the accelerating vehicle is increasing rather than decreasing up to the instant of impact Obviously our road surfaces nationally are not consistent and must be inspected personally by an expert in failed traffic safety. However, generally, paved road surfaces are not smooth; they consist of tiny rises and falls, (diagrammed in your work books)

As the vehicle is accelerating, remnants of the tire are scrubbed off leaving rubber against these tiny rises and falls. The rubber, which has piled up on the sides of the rises face in the direction of the vehicle’s travel.

The failed traffic safety expert will locate and face in the skid from the opposite direction of vehicle travel. The remnant mark will be darker at the start and fade out as it comes toward him/her because in reality the slippage of the tire against the road surface or surface tension lessens. While looking in the direction of vehicular travel, the marks will not appear as dark due to the simple fact that remnant rubber was deposited on the forward side of the hills and valleys of the road surface. Thus one can see less residual rubber (see Figure 3 in your workbook). Hot rod fans use skid readings to see where shifts are made when a car is accelerating. The acceleration skid marks darken where each shift is made. Increases torque on the rear wheels momentarily causing an increase in slippage and darkening the print from several inches to a few feet.

Braking Skid Marks

The remnant of braking skids are light at the beginning of the pattern and get darker at the end where the vehicle stops. This pattern develops due to the fact that the sudden braking (coefficient of friction between the road surface and the tire) causes enough heat to print part of the actual tire on the pavement left as a remnant rubber "finger print" (see Figure 4 in your workbook).

The Braking Skid or Deceleration skid marks will be noted as rubber remnant piled up on the backsides of the tiny rises and falls.

Gouge Marks

When a vehicle strikes an object, rolls over, or strikes another vehicle, metal parts of the vehicle will often gouge and scratch the road surface and fixed objects struck (please see Figure 1 in your workbooks). In Figure 1 an Angled front end fixed barrier collision visualizes remnant gouge marks and tiny remnant objects falling from the vehicle. Unlike a flush fixed end barrier collision where the damage is more confined. For example, major vehicle manufactures world wide only test fixed barrier studies. Obviously, the results are minor damage when compared to any similar speed vehicular collision during angled fixed barrier collisions. Death and sadness inevitably follows high speed to mid range fixed angled barrier front-end collisions. Thus, in a multi vehicular collision, if you are to recreate successfully the transpired events, tiny and minute remnants will denote strong viable evidence as to cause. You cannot be influenced by propaganda pseudo-science by either a major vehicular manufacturer or a pundit money doctor pro low impact high fatality ratios due to their obvious business intent to protect their profits. Absent any monetary compensation, the truth can easily be established.

These tiny gouge marks and striations will mark the exact point of impact and direction of travel after impact or roll over. Fresh gouges can readily be recognized, as old gouges, due to weathering and wearing (called spauling) will have smoother edges as opposed to fresh gouges, which are quite jagged.

As alluded to above gouge marks occur more frequently in high-speed collisions than in low speed collisions because in low speed collisions the forces are often insufficient to force metal to road contact from collapsing suspension components.

Impact Damage

The impact damage to any means of transportation can be observed visually. By covering all the bases as I am proposing, a combination of measurements of the damages with skid, gouge, striation and tiny remnants of the vehicles mark the angles of impact between the vehicular and a fixed barrier or a multi-vehicular collision. The amount of metal crushing involved can also be used to show the severity and speed of the vehicles at impact. The fact is that photographs of participating vehicles have proven extreme value due to this fact. Never, in these instances, have one quick snap shot taken, perhaps, a total loss worksheet. Thus, several clear photographs of the vehicles from every angle, from far to close, including above and below if possible are a must. Photographs of the actual accident scene surfaces will later denote lost remnant especially with super photo-focus technologies. Years later neither the vehicles nor the actual accident scene will be available or preserved and the photographs can be used to demonstrate visually what the expert witness is referring to!

In these cases, the services of a professional photographer are a must. If it is a severe accident with a large potential exposure, spend whatever money and time is necessary to rebuild a solid comprehension of the fact/evidence. A cheap expert witness’ investigation, unless there is no evidence, is usually worth less than you pay for it. It generally is a waste of time, money and effort. It has been the experience of our nation that only worthwhile cheap investigations are those that tells you that you have nothing to talk about.

In part two you will learn the forensics of Impact Damage, weathering, wear, head-on, rear end, T-bone, Fixed barrier Front end Angled vs. Flush pattern marks and Impact Damage with complete description and reconstruction diagrams of freeway and intersections. Further the taxonomy of twist, pulled, pushed and so forth Impact damages using actual past Legal Cases are correlated completely with consistent forensic principles of Justice through Science.

"God offers to every mind its choice between truth and repose. Take which you please-you can never have both." Ralph Waldo Emerson

-- Scott D. Neff, DC DABCO CFE DABFE FFABS FFAAJTS  Doctor of Medicine    

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