Event Data Recorders
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Most vehicles that are equipped with air bags also have a crash recording system known as an event data recorder (EDR). The EDR forms part of the computer system that controls deployments of the air bags and uses some of the available memory to store information about the crash. The data captured generally consists of information relating to the crash severity and to certain pre-crash actions of the vehicle's driver.
The stored data have a variety of uses, including refining the crash performance of active restraint components such as
seat belt pretensioners and advanced air bags, and enhancing collision avoidance systems such as electronic stability control and brake assist systems. In certain situations data obtained from EDR's can be used to support criminal and/or civil legal actions.
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How do they work?
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Sensors monitoring the vehicle's deceleration are used to determine when a collision is occurring, and the severity of the crash, in order to command deployment of the air bags. This process is conducted by an on-board microcomputer that controls the air bag firing circuit. Part of the computer's memory is also used to store information about the collision that can be downloaded and analyzed at a later time.
Some EDR's are proprietary and can only be accessed by the vehicle manufacturers. In contrast, some General Motors, Ford and Chrysler systems may be read by a publicly available tool, the Crash Data Retrieval System. The EDR is connected by cabling to a computer through an electronic interface device. Associated computer software allows data stored in the EDR to be accessed, downloaded to the computer. The program also analyzes the data and produces a report.
The data captured by EDR's generally consists of information relating to the crash severity and to various pre-crash actions of the vehicle's driver. There is currently no standardization of the devices. EDR's from different manufacturers, and even different models of EDR's from the same manufacturer, can record different types of collision data. Crash data can include such items as the vehicle's change in velocity (delta-V) and/or the vehicle acceleration as a function of time, and the firing times for seat belt pretensioners and air bags. Pre-crash data can include seat belt use (buckled or unbuckled), and a time history of vehicle speed, engine RPM, brake and throttle application. The following examples are taken from EDR's in General Motors' vehicles:
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| The EDR in this General Motors' product records the vehicle's change in velocity over a period of 300 milliseconds (thousandths of a second). The vehicle was involved in quite a severe crash, with a maximum change in velocity of 61 km/h (38 mph). Note that the change in velocity occurs quite rapidly, as shown by the steepness of the curve, before becoming constant at approximately its maximum value. The flat part of the curve at the end indicates that the speed of the vehicle is no longer changing, ie. the vehicle has stopped decelerating. The entire crash was over in just 140 milliseconds, a little over one tenth of a second! |
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The EDR has recorded the vehicle's speed (red line), the engine RPM (green line), the percentage throttle application (purple line), and the brake application (blue line) for a period of five seconds prior to the crash.
In the case collision, the vehicle driver was in the process of making a left turn in traffic. The vehicle speed ranged between 16 and 32 km/h (10 and 20 mph). Initially the driver was braking, prior to starting the turn, as shown by a nominal 100% application of the brakes five seconds prior to impact (t=-5s on the left of the chart). At the same time, there was no throttle application since the blue line starts at zero. The driver's foot then came off the brake and was placed on the accelerator (t=-4s). The vehicle accelerated and the engine RPM and the vehicle speed can both be seen starting to climb between t=-4 and t=-2s.
Because of oncoming traffic, the driver was clearly caught in two minds as to how to proceed. Two seconds prior to impact there was no braking and 100% throttle application, whereas at one second to impact the situation was reversed, with no throttle and the driver's foot back on the brake pedal.
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Data such as those shown above provide an objective record of vehicle crash performance, and of pre-crash driver actions, in real world collision situations. As such, these data are extremely valuable to a variety of end users. Vehicle manufacturers can use the data to improve the safety of their products, regulators can develop better crash tests and safety regulations, and researchers can explore driver behaviour in a way that has not previously been possible.
However, such information is also potentially useful to manufacturers in disputing frivolous product liability lawsuits, to police in prosecuting traffic offences, to lawyers and insurers in pursuing legal claims for damages resulting from collisions.
In general, the EDR and the data it contains belongs to the vehicle's owner. Consequently, access to the data is available to researchers only with the permission of the vehicle owner. But access to the data for legal purposes can be required if a court order to this effect can be obtained. This is a two-edged sword for vehicle owners. On the one hand, data from an EDR may be used as evidence to support a legal action, either criminal or civil, against a driver. In contrast, the EDR data may well support the driver's version of the events of a given collision and be used to defend against a legal action.
The bottom line is that your vehicle may be equipped with an EDR and, in the event of a collision, it may record some relevant data. One of the safety aspects of EDR's is that driver should be aware of the presence of an EDR and drive appropriately!
What can science tell us?
The Use of Event Data Recorders in the Analysis of Real-World Crashes;; German A, Comeau J-L, Monk B, McClafferty KJ, Tiessen P, Nowak ES, Chan J and Lo G; Proc. CMRSC-XII; London, Ontario; June 10-13, 2001
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The authors report on a series of test programmes and pilot studies of collisions involving vehicles equipped with event data recorders. These include instrumented crash tests which can be used to validate the quantitative results obtained from on-board recorders, and in-depth investigations of real-world collisions where results obtained using standard reconstruction techniques can be compared to the electronic data relating to crash severity. The studies also include an evaluation of pre-crash factors involved in real-world situations, based on in-depth investigation techniques, detailed occupant interviews, and analysis of a variety of pre-crash data elements obtained from event data recorders in collision-involved vehicles.
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Comparison of Crash Pulse Data from Motor Vehicle Event Data Recorders and Laboratory Instrumentation; Comeau J-L ; German A and Floyd D; Proc. CMRSC-XIV; Ottawa, Ontario; June 27-30, 2004
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Frontal barrier crash tests conducted with General Motors' vehicles allowed data relating to the crash pulse to be obtained both from the vehicles' event data recorders (EDR) and from the on-board instrumentation used by Transport Canada's test centre. Good agreement was observed between the two datasets; however, in some situations the vehicle EDR was found to be unable to capture the entire collision event. The implications for the use of EDR�s in real-world collisions are discussed in the light of these findings.
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A Study of Pre-Crash Events Using Information Retrieved from Event Data Recorders; McClafferty K, Tiessen P, Shkrum M, Chan J, Deyell P, German A, White J, Glazduri V, Comeau J-L and Monk B; Proc. CMRSC-XIII; Banff, Alberta ; June 8-11, 2003
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This paper reports on a series of in-depth investigations where pre-crash data was available from an EDR in at least one of the involved vehicles. In some cases, the electronic data confirmed the driver's recollection of the collision events, while in other cases there were significant discrepancies between the two data sets. Drivers tended to under-report their actual speed, braked late in the sequence of collision events, and drivers who were unbelted were frequently found to misreport their restraint status. Pre-crash information captured by current event data recorders is subject to a variety of limitations. Nevertheless, by providing objective data, these systems provide an extremely valuable tool for research into causal factors for motor vehicle collisions.
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Event Data Recorders: The Right to Privacy vs. Society's Right to Know; ; McClafferty K and German A; The Safety Network; pp. 7-9; June, 2004 (660 KB PDF file)
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This article expands on the finding of the above-noted paper and postulates that the safety benefits that may accrue to society as a whole from the use of EDR's are of greater importance than an individual's privacy in the context of existing limitations on the driving environment.
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A Review of Jurisprudence Regarding Event Data Recorders; Robert N. Green and Kevin J. McClafferty; Prepared for Road Safety and Motor Vehicle Regulation Directorate, Transport Canada; March 31, 2005
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The question of ownership of the EDR unit and generated data appears from the case law to date to abide with the vehicle owner. The rapidly evolving jurisprudence in both criminal and civil jurisdictions appears to significantly limit the owner to a reasonable expectation of privacy in allowing access to this data by many interested parties.
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Useful links
Safety Initiatives - Event Data Recorders (General Motors)
Q&As: Event data recorders (IIHS)
Event Data Recorder (NHTSA)
Event data recorder (Wikipedia)
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Quick Facts
- EDR's are present in many air bag equipped vehicles
- Many EDR's are proprietary and can only be read by the vehicle manufacturer
- Some EDR's from General Motors, Ford and Chrysler can be read by a CDR tool
- Data is captured on the nature of the crash and certain pre-crash driver actions
- Check the owner's manual for information about an EDR that may be in your vehicle
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