Archive for March, 2010

Valuable Evidence Collected from Vehicles

Wednesday, March 10th, 2010

As part of a thorough vehicle examination we will first look at the evidence that can be collected from the various lamps on the vehicle. Many times the question arises in an accident about whether or not someone had their headlamps on low or on high beam. Were they using their turn signal? Or were other basic indicator lights illuminated? Sometimes as a result of the collision there may be scientific evidence that may be collected from a bulb or even its remnants that could help answer these question

Second let’s consider the vehicle’s tires. Depending on the circumstances surrounding the accident there may be questions about tire failure. Valuable evidence regarding this can be collected from a careful inspection. Also the tires could be overly worn or improperly inflated and lead to a hydroplaning incident. Or maybe the tires are unevenly worn indicating a possible alignment issue. Also it is important for accident reconstruction purposes to know if the wheels became pinned or locked due to the collision because this affects the post-impact energy-speed calculations.

Next we can look at the damaged areas. When considering vehicle damage it is important to distinguish between contact damage and induced damage. As the terms imply, contact damage is damage to a vehicle caused directly by contact with another vehicle or object. Induced damage is damage that is produced by the collision forces but did not directly make contact with any outside object. Some items of evidence that can be collected from damaged areas include surface abrasions, windshield damage, imprints, tire prints, and paint transfer. Also we want to measure the crush profile and determine the principle direction of force.

 

Surface abrasions usually result when a vehicle overturns but can result when a vehicle scuffs up against an object or rigid body such as a median wall. When the vehicle slides over a surface it will produce scratches in the vehicle’s paint. The orientation of these scratches can be helpful in determining the movement of the vehicle as the marks are being made.  

With windshield damage it is important to distinguish between induced and contact damage. It is also important to note that some windshield contact damage can result from the deployment of vehicle airbags. If it is determined to be contact damage not from an airbag, it could be from an object outside the vehicle such as a motorcycle or bicycle rider. In this case it would indicate the movement of the rider after the impact with the striking vehicle. The windshield damage could also result from an occupant or some other object inside the vehicle. This information can help determine occupant position and the direction of the collision forces.
Tire prints are similar to imprints however they do not typically leave an impression but a different kind of distinct marking. Sometimes during a collision the tires of one vehicle will rub up against the body of the other leaving a rub mark or tire print. In the case where the front wheel of a semi-tractor rubs up against a vehicle, the lugs can produce circular tears in the metal along with the tire rub mark.

 

 

 

Another bit of evidence that can be helpful in determining the orientation of the vehicles or even which vehicle hit another vehicle at different points in a multi-vehicle accident is paint transfer. Many times paint from one vehicle will be transferred onto the other vehicle where they make contact. Although many times this evidence may be obvious there are other times where it is very miniscule and requires careful examination.

Finally by looking at and taking measurements of the damaged vehicle we can produce a scale diagram of the vehicle and its deformation. This is helpful like the tire prints and paint transfer in determining the way the vehicles came together in the collision. Also it can sometimes be used with crash test data to determine an impact speed for the striking vehicle. Also we can look at different components of the vehicle that were displaced during the collision and take note of the direction of their displacement from their original placement to get an idea of the principle direction of force that was applied to the vehicle. This can be helpful in confirming other calculations and in understanding occupant kinematics.

 

This article is not exhaustive but serves to highlight the fact that a lot of valuable evidence and data can be obtained from a careful vehicle inspection. This information can assist in answering questions that arise when investigating the causes of vehicle accidents.

 

Jonathan McGehee