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Crash Data Recorders: The New Eyewitness In Vehicular Accidents As originally published in Advocate Magazine, Summer 2001
By: Dr. George Govatos |
THOSE OF YOU WHO PRACTICE AUTOMOBILE LAW ARE ABOUT TO EXPERIENCE A PROFOUND shift in the way accident cases are litigated and settled. The field is on the verge of a technology driven paradigm shift that will have an immediate and lasting effect on the way crash related evidence is measured, recorded, collected and analyzed. The story of this change involves the vehicle airbag; more specifically, the sensors and conrrol modules that monitor vehicle status and decide when the airbag should deploy. These modules are the aviation equivalent of "Black Box" data recorders that store and later provide vital information about the status of the airplane in the moments prior to disaster. We are now learning that airbag control modules have had the abiliry to provide similar data for vehicle crashes at least since the early 1990's. Methods for retrieval of these data are now commercially available and are currently being used as the equivalent of mechanical witnesses to tell crash investigators what happened in the moments prior to a vehicle crash.
Overview of the Technology
Since the advent of airbag technology in the mid 1970s, engineers have had to develop and refine a method for sensing vehicle status so that airbag firing circuits could determine whether or not to deploy the airbag. Specifically, the control circuits had to be able to discriminate berween normal driving conditions, and the initial stages of an impact that would require airbag deployment. To help increase their knowledge of the dynamic states of the vehicle, sensors, along with memory units, were designed to record and store some parameters associated with airbag deployment. These data could later be retrieved and analyzed ro refine discriminatory conditions for sensing and firing the airbag.In 1990, General Motors introduced a Diagnostic and Reserve Energy Module (DERM) that recorded airbag firing data and fault codes within the airbag firing system. In 1994, General Motors introduced a single point sensing system consisting of a solid state analog accelerometer and a computer algorithm integrated into a Sensing and Diagnostic Module (SDM). This system allowed recording and collection of data regarding maximum velocity change (delta V) of the vehicle for both deployment and near deployment events. Since historically, delta V has been used as a measure of crash severity this allowed engineers to learn how the entire restraint system, including belts and airbags functioned with changing crash severity conditions.
In 1997, the National Thansportation Safery Board (NTSB) made a recommendation that vehicle manufacturers and the National Highway Traffic Safery Administration (NHTSA) work together in collecting and using these crash data to increase highway and vehicle safety. In 1999, General Motors expanded the capabilities of the SDM allowing it to collect precrash parameters including vehicle speed, engine speed, throttle position and brake activation for a duration of 5 seconds prior to deployment or a near deployment event. A summary of the data collected and recorded by the 1990 DERM, the 1994 SDM, and the 1999 SDM is shown in Table 1.
Although these data were recorded, they could only be retrieved and interpreted by General Motors technicians using specialized equipment. To make these crash records available to the general public, General Motors authorized Vetronix Corporation of Santa Barbara, California to develop the hardware, software, and connecting cables to download and analyze recorded data from the SDM. Last year, the Vetronix Crash Data Retrieval System became commercially available, and is now being used by police agencies and others engaged in accident reconstruction to assist in reconstruction of accident events.
The amount and type of data that can be downloaded varies according to the rype of SDM in the vehicle. Not all 1999 models store the complete data set shown in Table 1. However, in succeeding years, 2000 and 2001, the number of General Morors cars offering the complete data set has increased. Vetronix has stated that subsequent versions of the Crash Data Retrieval System will be able to collect data for previous years through 1990 for all General Motors cars equipped with recordable modules. In addition, Vetronix has designed their Crash Data Retrieval System such that it can be used to retrieve data from other manufacturers by simply updating the software. Vetronix expects to begin to add models from Ford Motor Company by the end of 2001. Because of the recommendations from the NTSB and the NHTSA, it is expected that all manufacturers will soon be making recorded crash data available.
Dr. George Govatos has provided Engineering Analysis for attorneys, both plaintiff and defense, and Engineering Design / Analysis for public and private clients for over 27 years. He also lectures in the fields of Accident Reconstruction and Collision Analysis, Highway Safety, the mechanics of whiplash, structural collapse, and engineering aspects of product liability.
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