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Pre-crash path determination using EDR stability control data

Author(s): Agha-Razi

Slidedeck Presentation Only:

1B_Agir-Razi

Abstract:

Background/Context: Event Data Recorder (EDR) contains large number of recorded data that can be used to reconstruct events leading to a collision. Often collision investigators only use the reported speed as the main element in their analysis. However, other data such as stability control, yaw rate and steering input can be utilized extensively. A vehicle's path of travel can be determined using the stability control yaw rate in concert with steering input analysis.

Pre-crash path determination using Event Data Record (EDR) is especially necessary in cases where encroachment is suspected. Often in cases of encroachment which lead to a head-on collision, investigators are left with little to no road evidence other than what is left at the point of impact.

Physical evidence of the roadway such as tire marks is often not available either due to its short longevity or its weather dependency. Important physical evidence is often disturbed during rescue attempts by the emergency personnel.

The need for an independent and reliable method to determine the path of a vehicle prior to collision resulted in the research and development of this mathematical method.

Aims/Objectives: This method enables investigators to accurately determine the path of a vehicle using stability control yaw rate and steering input recorded by the Event Data Recorder (EDR). The path is then complimented by road evidence, witness statements, crush analysis and can be superimposed on the scene diagram to produce reliable results. This is especially important in cases where encroachment is suspected and road evidence is limited or short-lived.

Methods/Targets: In normal driving conditions, a driver steers the vehicle between two points in a slightly curved path and constantly 'corrects' the heading of the vehicle to navigate the roadway and negotiate the turns. In other words, the vehicle travels from point 'A' to point 'B' at a 'Rotational Speed' of “ω”. Its actual path is a curved line between the two points. If the EDR download includes information about stability control yaw rate (in degrees per second) it means that a built-in gyroscope has measured its rotational velocity (angular velocity) around its vertical axis as the vehicle was being driving on the roadway. This data is usually recorded every 0.1 second.

In this method rotational speed is converted to a linear speed using basic geometry. The resultant linear speed ''vector'' has both magnitude and direction; The vector is then projected into two components of X and Y to get the lateral and longitudinal movement of the vehicle for the duration of the EDR pre-crash download every 0.1 seconds. The calculated points are then compiled and the path is drawn using the coordinates.

Results/Activities: This method produces accurate and reliable results which matches closely with steering input analysis.

This method can also pinpoint exact coordinates of the beginning and end of a yaw mark which can be valuable when the road evidence and tire marks are disturbed by emergency personnel or environmental factors.

Discussion/Deliverables: This method is a valuable tool in cases of head on collisions where encroachment is suspected.

The threshold where this method loses its functionality is when the vehicle starts leaving yaw marks and striations on the road. This method would be redundant if the vehicle in question leaves yaw marks that show the path of travel at the time of the collision.

Effects of extreme avoidance maneuvers (over-steering); high-speed cornering, spin outs as well as correction for road geometry of a vehicle in yaw (i.e. superelevation) will be discussed in future documents.

Conclusions: This method provides a valuable tool to collision investigators that is reliable and easy to understand. It will also allow the investigators to cross reference their findings and prove validity of their analysis when speed determination, yaw analysis and steering analysis all yield the same results. Using this mathematical formula, the investigator will be able to accurately draw and explain the path of travel with X-Y coordinates for technical and non-technical audience.