File Name: evidence in traffic crash investigation and reconstruction .zip
What is Accident Reconstruction? Accident reconstruction is the process using scientific methodology to determine the circumstances, mechanics, and contributing factors associated with a collision. It requires a working knowledge of many disciplines including physics, vehicle dynamics, mathematics, photogrammetry, and computer applications i.
This article presents several basic concepts typically found in the area of investigation and reconstruction of vehicle collisions. The following material is not intended to be comprehensive, but should be considered an overview of fundamental principals. These concepts are presented as they commonly apply to collisions involving passenger cars.
Other areas of analysis not included are collisions involving heavy trucks and other articulating vehicles, or impacts involving pedestrians, motorcycles and bicycles.
Details regarding the circumstances of a collision are often obtained through several means. Two basic sources of information are the Traffic Collision Report, and photographs of the vehicles and collision scene. Additional sources to be considered are witness statements and deposition transcripts. Oftentimes the eye witnesses may fill the gaps between what can be observed in photographs and what the traffic officers included in their reports.
Emergency personnel run-sheets, medical records, and autopsy reports can provide useful and thorough descriptions of occupant injuries. Injury location may be used to help support opinions regarding vehicle dynamics. Repair estimates, crash test reports, and vehicle specifications provide data necessary for calculations when vehicle weight, dimensions, and property damage are used. Published research and literature can help assist the reconstructionist when a specific engineering principal or phenomenon is being analyzed.
Inspection of the collision vehicle is most helpful when performing a reconstruction. While the study of photographs of vehicle damage is important, many details about the degree of vehicle deformation can be vague or not fully documented in such photographs.
Therefore, a vehicle inspection is often preferable. If a two-vehicle collision is being analyzed, inspection of both vehicles should be requested. This often requires additional leg work, because the location and condition of the other vehicle are seldom known. Vast amounts of information can be gleaned by inspecting the collision vehicle, such as the quantification of the vehicle crush profile.
In addition, simply standing next to, or even sitting in the damaged vehicle and considering the extent and direction of the structural deformation lends crucial insight into collision type and severity. What can be learned at an inspection that cannot be learned from reviewing vehicle photographs? One example is the confirmation of ground contact to the vehicle undercarriage. Colliding vehicles will often pitch downward during the collision phase to the extent that suspension members or other undercarriage components strike the road surface and create a gouge.
Along with pre-impact skid marks or post-impact tire marks, gouge marks are often among the list of physical evidence documented by the investigating traffic officer.
Determination of which vehicle component interacted with the roadway and their location relative to some vehicle-fixed reference point may support opinions regarding vehicle position and heading at the time of impact.
Photographs of the accident vehicles rarely depict undercarriage damage. Another example supporting the utility of vehicle inspections can be the existence of grass or debris trapped in door openings. The existence of this material may help to confirm the door came open during the collision or rollover event. Even grass or dirt embedded in the junction between the tire bead and wheel rim may help confirm tire separation during the collision as opposed to this occurring during vehicle storage after the tire goes flat.
Oftentimes, photographs do not yield this level of detail, and inspection of the vehicle is the only way to confirm these potential phenomenon.
Because evidence inside or outside the vehicle can only degrade with time, a secure and indoor vehicle storage is strongly recommended. Proper vehicle storage should be considered sooner rather than later. The results of the collision reconstruction may include pre-impact speed, vehicle heading, post-impact speed, and change of velocity or delta-v.
The principal direction of force, collision duration, and peak or average vehicle acceleration may also be evaluated. However, before one can fully comprehend the significance of the terms commonly used by reconstruction specialists, a review of fundamental terms and units may be helpful. Four fundamental physical parameters are length, time, force and mass.
Typical units for length or distance are inches, feet, or meters. For time, seconds are commonly used. The units of force are pounds or Newtons; for mass, slugs or kilograms. Derived terms are algebraic combinations of the four fundamental parameters.
Derived terms commonly used by the reconstructionist are velocity, acceleration, energy work , and momentum. Acceleration is the rate change of velocity with respect to time, or length per unit time squared.
Speed and velocity are different entities, although in colloquial speech these two words are often, although inaccurately, used interchangeably. By definition, speed is a scalar quantity having only magnitude. Recall that speed is the rate change of distance. However, velocity is also the rate change of distance, but velocity is a vector quantity with magnitude and direction.
Several other important terms include delta-v or Dv , principal direction of force PDOF , center of gravity, yaw, coefficient of restitution, and coefficient of friction. Delta-v is the vector difference between the pre-impact and post-impact velocities, or the velocity difference between when the vehicles first come in contact to when they separate. Of note, the time between first contact and separation is called the collision phase of the impact, the time during which the vehicles deform.
Therefore, by definition, Dv does not include any pre-braking speed loss or speed lost by the vehicle after separation before coming to rest. The PDOF is the direction of the summation of all collision forces required to deform the vehicle. When two vehicles come in contact, they begin to deform at some force level. The surfaces of each vehicle in contact change over time, because of vehicle deformation, and they continue to change throughout the collision phase.
As an analogy, picture two rectangular sponges being pressed together. Initially, the two sponges may touch at the corners, or at each end, but with increased force, the area of the contact surface of each sponge increases.
Similar in concept to the sponge, the structure of a vehicle deforms in an impact. Forces are required to deform a vehicle structure, however over the collision phase, the forces change direction and magnitude. As the vehicles continue to engage, new structures are deformed. Instead of analyzing the work and moment contributions of all these collision forces over all the directions of the impact, reconstructionists study the one collision force applied to the vehicle along the principal direction of force.
The direction of the PDOF is often given in terms of degrees or hours of a clock dial. The center of gravity, or cg , is simply the balance point of a vehicle. To simplify the analysis of a colliding vehicle, the entire mass of the vehicle is defined to be located at the cg.
One can calculate the fore-aft location of the cg by applying a moment balance using the front and rear axle weights. However, vehicle occupants can shift the cg fore or aft to some degree, and the apportionment of passenger weights to the front and rear axles should be considered. Also, the cg may actually be slightly to the left or right of the vehicle centerline, but for most applications one can assume the cg is centered laterally.
Yaw is rotation of the vehicle about a vertical axis passing through the vehicle cg. This curved path is indicative of a vehicle in yaw. Yaw will be studied in a misapplication of the skid to stop equation presented later. Restitution is why vehicles often bounce away from the other vehicle or rebound from a rigid barrier after an impact.
Vehicle collisions are called inelastic, and property damage often results. However, while the vehicle structure does deform, there is some portion of this damage that is restored. The restoring forces are what cause restitution.
The coefficient of restitution of two colliding objects is defined as the ratio of the relative rebound velocities to the relative impact velocities. The coefficient of restitution, commonly given the variable name e, is unitless and can have a value of between 0 and 1.
For two colliding vehicles, the equation for coefficient of restitution can be written as:. When a vehicle impacts a rigid barrier, the equation simplifies to:.
By way of example, vehicles impacting a rigid barrier at 30 to 35 mph exhibit restitution values of between about 0.
However, as collision speeds decrease, restitution often increases. For this reason, it is crucial to have accurate values of e when studying a low-speed collision. The coefficient of friction is why vehicles slow down, upon applying the brakes. The friction coefficient is also a unitless value. It is often given the variable name F , and is a measure of the relative slipperiness of two surfaces in contact.
In the case of a vehicle in a locked-wheel skid, the two surfaces are the roadway and the tires. However, more accurate friction coefficients for a specific road surface may be obtained by conducting a brake test with an appropriate exemplar vehicle. Special consideration must also be used with ABS equipped vehicles. This equation can be used for any condition when a vehicle changes velocity.
With strict adherence to the sign of the velocity and acceleration terms, this equation can be used not only for the slowing vehicle, but for the vehicle increasing in velocity as well. The general velocity equation is often applied to vehicles braking to a stop.
In this case, v f is zero, so the general equation simplifies to the skid to stop equation:. The general velocity equation can be rearranged algebraically so the value of v f , v i , a or d can be solved. Two examples will be used to illustrate this point.
These examples are theoretical or text book applications of the general velocity equation. Consideration must be given to real world braking system components. For instance, vehicles do not leave skid marks immediately upon stepping on the brake pedal. The rotating wheels need time to slow and lock prior to leaving tire marks.
Estimates can be made of the distance necessary for a vehicle to skid to a stop based on a pre-braking speed and a friction coefficient. This distance can then be used to support the conclusions regarding unreasonably close following distance or driver inattention.
What is Accident Reconstruction? Accident reconstruction is the process using scientific methodology to determine the circumstances, mechanics, and contributing factors associated with a collision. It requires a working knowledge of many disciplines including physics, vehicle dynamics, mathematics, photogrammetry, and computer applications i. This article presents several basic concepts typically found in the area of investigation and reconstruction of vehicle collisions. The following material is not intended to be comprehensive, but should be considered an overview of fundamental principals.
The manual also discusses the importance of calling upon the skills and advice of occupational specialists, such as reconstructionists, lawyers, traffic engineers,.
Firmware update 5. Evidence Recorder V
Currently the unit includes 12 Troopers, 14 County deputies, 32 Municipal officers, and 2 Game Wardens. Unit members are located throughout the entire state and are chosen based on both geographic location and ability. The objective of the Crash Reconstruction Unit is to conduct in-depth investigations and analyses of major traffic collisions throughout the state.
Traffic collision reconstruction is the process of investigating, analyzing, and drawing conclusions about the causes and events during a vehicle collision. Reconstructionists conduct collision analysis and reconstruction to identify the cause of a collision and contributing factors including the role of the driver s , vehicle s , roadway and general environment. Physics and engineering principles are the basis for these analyses and may involved the use of software for calculations and simulations. Collision reconstruction is sometimes used as the basis of expert witness testimony at trials.
Providing tailored solutions for the investigation of incidents involving road users of all types, ranging from a full analysis to answering specific questions about an incident. We supply court-ready reports and provide live evidence in Civil, Criminal and Coroners Courts. Our expertise covers; Vehicle Examinations Mechanical road worthiness examinations, damage analysis and component failure examinations. This is an area where FCIR stand out combining knowledge of both vehicle condition and the collision dynamics. This is important because whilst there may be a defect to a vehicle it requires knowledge of both the vehicle and the collision to state if these were contributory to a collision.
Да, да, - сказал он, - читайте эту благословенную надпись. Сьюзан стояла рядом, у нее подгибались колени и пылали щеки. Все в комнате оставили свои занятия и смотрели на огромный экран и на Дэвида Беккера.
Your email address will not be published. Required fields are marked *