- The #1 Mistake Accident Investigators Make When Using EDR "Black Box" Data:
Accepting the data on its face value!
The data retrieved from an electronic data recorder (EDR) is relative data, insomuch as the data is generally going to be accurate to what the sensors are telling the EDR. The manufacturer of the vehicle from which the EDR is installed may go so far as to include a disclaimer in the EDR report retrieved with the Bosch Crash Data Retrieval (CDR) Tool cautioning those reading the data to always compare the data reviewed against the actual scene evidence. That is, to use the physical evidence to validate the EDR data, and not the other way around.
Take speed for example, vehicle sensors have no way of knowing whether the wheels are rolling on the pavement (a normal “static” relationship), slipping on the pavement (as in a loss of traction), or free-wheeling (spinning while the wheels are off of the ground). The speed data reported may be from one or several sensors. And, most importantly, the speed reported has no spatial reference, meaning, that if the vehicle is in a yaw, the speed sensors may not be giving you the true speed of the vehicle’s center of mass.
EDR data may be of value in helping to determine the speed of the opposing vehicle. This is accomplished by using the EDR’s reported change in velocity along with the weights of the vehicles to determine the change in velocity for the other vehicle. The result can then be used with other calculations to determine the closing speed. That information, along with other data, can then be used to determine the approach speeds. The problem, however, is that there is a significant margin of error that must be kept in mind so as to determine the range of possible speeds.
Information the analyst needs to complete their work can often be found in the CDR report’s “Data Limitations” section. However, many do not take the time to review this information, leading to improper conclusions. For example, if the EDR reports steering wheel angle, knowing whether the proper sign convention (+/-) is applied to the data can make the difference between a proper or improper determination of the direction the operator is attempting to go. Additionally, the steering wheel angle reported in an EDR is not the actual bearing of the vehicle, but rather just the angle the steering wheel is turned. The resolution of the steering data may indicate the wheel was turned 10 deg, when in reality that value may cover a range of 5.01 deg to 10 deg. Without reading the Data Limitations, the analyst may not know whether this is true.
The truth is that there are many factors which must be taken into account when evaluating EDR data. Choosing to rely on the data on its face-value is akin to playing Russian Roulette. Can you really afford to make that mistake? We owe it to ourselves to be continually aware of not only the applicability of technology, but of the changes and advances the tech goes through. Never stop learning!
- Excellent points!
EDRs are an excellent supplement to the crash investigation and reconstruction field.
However...
they are NOT infallible.
We wrote a paper last year on some of the possible issues and will be presenting more EDR related findings at the 2024 IPTM Symposium...
- 109 MPH Crash, Collision Magazine Article, msmac3D Recon
- Which includes a link to our article
- Investigation of EDR Data from a High-Speed Crash with msmac3D
- Please let us know if you have ANY questions or comments on the article!