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Gary Kilpatrick, PE, NSPE

A Traffic Accident Reconstruction is a process by which an engineer determines from all available information and evidence how and why a traffic accident occurred including but not limited to pre-impact and post impact vehicular velocity vectors, pre-impact and post impact vehicular direction vectors, vehicular change in velocity (Delta-V), momentum vectors, vehicles' point of impact on the roadway, vehicular visibility by a driver, vehicular crash data retrieval reports if assessable, accident factors and causes. Traffic accident reconstruction is a complicated science. The following is only a synopsis of the science for the interested reader of a traffic accident where one or more cars, light trucks or road tractors and semi trailers are involved in a collision.

Phase One: A meeting is scheduled between the engineer and the client to discuss the traffic accident case at hand. It is here that the client will discuss with the engineer the details of the case and what type of information the client is looking to discover or prove.

Phase Two: If the traffic accident took place in the past, the engineer will requst and review all non-privileged arguably relevant documentation given to him by the client if it is available such as pleadings, depositions, interrogatories, police citations, a police wreck report, police or legal counsel accident photographs and if available a police accident reconstruction report. It is during this phase that the engineer will have to determine if there is enough informaton and evidence to reconstruct a traffic accident. From the time an accident takes place, the accident site evidence will deteriorate quickly due to other vehicles driving up and down the road as well as ambient weather conditions such as rain and wind events. These things quickly deteriorate tire skid marks and evidence of soil that was disturbed by vehicles sliding, vaulting or flipping on asphalt, grass or dirt surfaces. If the traffic accident took place several months or years in the past and all of the physical evidence has since then disappeared, the engineer will have to make a decision as to whether or not there is enough documented evidence for a traffic accident reconstruction. If he deems there is enough evidence, he will then proceed to Phase Three.

If the traffic accident has just taken place and the engineer is contacted and retained to assist a private party, legal counsel or law enforcement in a traffic accident reconstruction, then the above stated documentation will not exist, and the traffic accident must be reconstructed from vehicle inspections and accident scene evidence inspection.

Phase Three: The engineer will interview the investigating police officer, witnesses if any were present during the accident and the person or persons represented by the client, if and only if, the client has given the engineer permission to do so.

Phase Four: Research the vehicles involved in the accident to determine if they are equipped with airbags and seat belt pretentioners. Also determine if the vehicles are assessable to the Bosch Crash Data Retrieval System. If the vehicles have air bags and are assessable, then the engineer must determine if he has has the appropriate umbilical cables for the Bosch Crash Data Retrieval System. If not, the engineer must order and purchase it. The engineer will then travel to the vehicle manufacture dealership to obtain vehicle build sheets and ACM wiring information. If the vehicles have airbags and selt belt pretentioners and are assessable by the Bosch Crash Data Retrieval System, then the engineer must get written approval from his client and the owner of the vehicle to enter the vehicle and download the crash data report. In some states, it may be required to obtain written approval from each owner of the vehicle if the vehicle has been owned and operated by various individuals.

Phase Five: The engineer will then travel to where the vehicles are being stored and inspect, measure, photograph and record in detail the following: crush damage present on the body of each vehicle and crush damage measurements, damage to the vehicle's chasis, the interior damage and seat positions, body paint damage, scratch and scuff markings and their directions and orientation, window glass damage, tire wear, tread scuffing and tire damage, tire size and type specified by the manufacturer, tire air pressure if the tires are inflated, soil/grass/asphalt imbeded into vehicle chassis and body parts, engine coolant radiator and engine oil pan damage and service brake system condition. The engineer will also determine the approximate principle direction of force generated on each vehicle. Traffic accidents involving road tractors and semi-trailers are special cases of a traffic accident reconstruction and require a full and complete inspection of the entire rig including all damage, the brake system, its air tanks and lines, glad hands and electrical connections, slack adjusters and brake lining, the lamps on both the road tractor and trailer. To obtain a download of the road tractor's event data recorder, special computer equipment is needed to acomplish this. Both the road tractor and semi-trailer must meet the requirements of the U.S. Department of Transportation's Federal Motor Carrier Safety Administration.

The engineer may determne that a component failed and caused the accident. The engineer will then contact the client to discuss this issue and to get permission from the client to have the vehicle towed to a dealership's service department for a vehicle component disaasembly and inspection. The engineer must not perform this inspection without the client's approval.

The engineer will create hard copies of his post-collision vehicle photographs along with any other photographs taken by law enforcement, the plaintiff or legal counsel and take them to the accident site to assist him in the accident reconstruction process. He will look at these photographs while he is at the accident site along with viewing the tire skid marks, and gouge and scrape marks on the roadway to determine how the vehicles approached each other, collided with each other, separated and traveled to their resting places.

Crush measurements are useful for input into dynamic vehicle crash analysis and simulation software. This program incorporates vehicle body crush coefficients, and vehicle dynamic yaw, roll-over or flip equations for the calculation of vehicle velocities and dynamic video simulation. Gary E. Kilpatrick and Associates, PA utilizes this software for traffic accident reconstruction along with in-house created crash programs. Visit the website of Engineering Dynamics Corporation to read about our software and this technology. We have also created our own vehicle velocity program to calculate vehicle speeds at impact.

If the vehicles have occupant restraint system technology (air bags and seat belt pretensioners), a vehicle crash data report may be stored in the Airbag Control Module (ACM) or Power Train Control Module (PTCM). The engineer can download the stored crash data report by utilizing the Bosch Crash Data Retrieval (CDR) System for cars and light trucks. Once the engineer downloads the report into his or her laptop computer, he or she can then view and interpret the report. This crash data report download can be performed if and only if the data is accessible. At this time, only General Motors, Ford, Chrysler, Isuzu, Mitsubishi, Sterling, Suzuki, Saab and Hummer vehicles are accessible using the Bosch Crash Data Retrieval System. The engineer can utilize an autoscanner to download any Diagnostic Trouble Codes (DCTs) via the vehicle's Data Link Connector if its wiring is intact. Visit the website of Bosch Diagnostics to read about this technology. Click on CDR to read about this forensic engineering service we provide as well as a discussion for a vehicle crash data report download. For all other non-assessable vehicles that utilize occupant restraint system technology, their vehicle crash data reports may be downloadable if available at a manufactures dealership by a certified dealership technician utilizing the manufacturers certified equipment. The Bosch CDR system mentioned here will not interface and download crash data from Road Tractors. This has to be performed using special systems that are made for this purpose. These systems may be purchased from the truck manufacturer or other suppliers.

If the accident took place during the night time hours, questions may arrise as to whether a vehicle's lamps were on during a collision. While inspecting the vehicles, the engineer will be in a position to perform a lamp filament anaylsis. However, due to outside lighting and ambient conditions and/or lamp proximity within the vehicle, it may be necessary for the Engineer to remove the lamps from the vehicle and perform the lamp filament analysis in his office or lab under controlled lighting conditions as well as the ease of handling and manipulation of the lamps. This analysis will determine if the lamps were on or off during a night time collision. Click on this link Lamp Filament Analysis to read about this forensic engineering service as well as a synopsis of the science.

If there was more than one occupant in a motor vehicle, questions may arrise as to who was actually seated in the driver's seat driving a vehicle. The engineer will inspect and record the seat positions, interior impact damage, blood and tissue spatter. If the occupants were injured during the accident, the engineer may be able to compare and match up their injuries to the impact areas along with interior damage. If one occupant was heavy or thin, short or tall, seat positions along with bodily injuries, interior impact damage and body DNA analysis comparison can indicate who was actually driving a vehicle.

Phase Six: The engineer will travel to the accident scene and walk the entire site to carefully inspect the actual physical evidence of the accident site including but not limited to the area of impact of the vehicles, fluid stains from engine oil and coolant, tire skid marks on the roadway surface, tire skid marks on the dirt or grass, gouge or scrape marks on the road surface, dirt or grass, vehicle impact gouges on the roadway, dirt or grass shoulder from impact from a vehicle, pre and post impact trajectories of each vehicle, property damage, location of vehicle parts and each vehicle's final resting place including human bodies if anyone was thrown from the vehicles or struck and thrown by a vehicle, the surrounding landscape and topography, the location of all signage adjacent to the accident scene such as stop signs and other road signs, utility poles, buildings, trees and shrubbery adjacent to the roadway, sight obstructions such as buildings, signs, trees, shrubbery and other structures that could impede the visibility of drivers at the accident sight. The engineer will also confirm the principle direction of force generated on each vehicle.

The engineer will create a scaled Accident Scene Situation Map to capture and record the accident scene and all evidence on a drawing. This Accident Scene Situation Map will include but is not limited to a reference point such as a utility pole, a building corner or some other point that the engineer chooses, the roadway surface and its boarders, its curvature if any, the road surface flatness or crowning, the surrounding landscape and topography, the location of all signage adjacent to the scene such as stop signs and other road signs, utility poles, buildings adjacent to the roadway, sight obstructions such as buildings as well as other structures, signs, trees, bushes and shrubbery, the area of impact of the vehicles along with a sketch of the vehicles' approach, impact and separation, tire skid marks on the road surface, dirt or grass, gouge or scrape marks on the road surface dirt or grass, the trajectories of each vehicle, property damage, location of vehicle parts and each vehicle's final resting place including human bodies if anyone was thrown from the vehicles.

The scene map is a living document during the traffic accident reconstruction effort where forensic evidence and information are continuously added throughout the reconstruction effort as the scene is inspected and measured. When the engineer has finished creating the Accident Scene Situation Map, it will be a scaled drawing of the entire traffic accident site. The map will include a measurement chart that indicates drawing scale, measurements, directions and distances for each point measured which is indicated on the map. The map will also include an identification block to identify who performed the reconstruction effort and the date it was performed. There are various methods to create these maps. One way is to draw the map free hand on a sketching pad. Another way is to create a scaled instrument drawing on site utilizing a portable drafting machine. The engineer can utilizes a laptop and CAD software to create the map. The engineer can utilize a computerized surveying instrument called a total station to establish a point cloud of the traffic accident scene which can then be uploaded into a CAD system for drawing rendering. Another way is to utilize Close Range Photogrammetry which generates similar points as the Total Station for drawing rendering. Another service we provide is a 3-D laser scan of the entire accident site if the client requests it. This scan will generate a complete 3-D image of the accident site that can be rendered to do a virtual walked through.

The engineer will photograph the entire accident site including all evidence and indicate by markers at the site and on the Accident Scene Situation Map the approximate locations where he took each photograph. He may also video tape the site as well.

As stated above in Phase Two, from the time an accident takes place, the accident site evidence will deteriorate quickly. If the accident took place several months or years in the past, the physical evidence at the accident site will have deteriorated and disappeared. The engineer will then need to utilize his skills of photogrammetry for a photo reconstruction if and only if good quality photographs exist. This is where an attempt is made to extract physical evidence from old photographs taken at the traffic accident scene just after the accident took place. Computer programs exist today that can assist the engineer in photogrammetry such as iWitness. Another technology is the 3-D Laser Scan. Click on this link to review information about this technology 3-D SCAN. As stated above in Phase Two, the engineer must make a decision early on as to whether or he has enough information and evidence to reconstruct a traffic accident.

Note: The engineer may be required to perform field test using exemplar vehicles to determine additional information if documented data is not available. The client must approve this before hand. The engineer must also consider Human Factors during the traffic accident reconstruction such as driver perception and reaction time, vision and visibility and his or her movement within the vehicle and interior damage related to bodily injuries. Seat position is noted in an attempt to determine and verify who was driving if there are questons as to who was driving the vehicle during the accident. If the Engineer determines that visibility was a factor in a traffic accident, then the engineer will be required to perform studies using exemplar vehicles to determine when the vehicles were and were not visible to the drivers involved at a accident site. Depending on the case, the engineer may determine that a vehicle component failed in service causing the accident. If this is the case, then the Engineer may be required to disassemble parts of a vehicle, with the approval of the client, to locate the components that failed causing a traffic accident for the purposes of a product defect and failure investigation. Click Product Liability to read about this forensic engineering service.

Phase Seven: The engineer is now in a position to return to his office and start his reconstruction analysis of the vehicles involved in the traffic accident including a vehicular velocity analysis and a dynamic computer simulation and study. This analysis will determine if a vehicle was speeding, exceeding a safe speed, if a vehicle ran a stop sign or red traffic light or if a driver lost control of the vehicle due to a component failure. The engineer will calculate the pre and post impact vehicle velocities and determine how the traffic accident transpired. As a final note, remember that it is impossible to defy the laws of physics. Click on this link The Physics of a Collision to read about the engineering sciences regarding velocity calculations.

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Gary E. Kilpatrick and Associates, PA, is a Forensics Engineering Firm dedicated to the application of the art, science and methodology of engineering and the scientific method to answer questions of fact in the jurisprudence system pertaining to personal injury and wrongful death.

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