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Vehicle Data – The final answer or just the beginning

February 26, 2018

Does the “black box” in a vehicle hold all the answers or does it precipitate more questions?

Most vehicles on the road today have an event data recorder (EDR), and the number of EDRs is only increasing as newer vehicles replace older models. EDRs are modules that will record data related to an incident (i.e. a collision). This technology has been around for over 20 years, so now is a good time to look back at how these black boxes have changed the way we investigate collisions.

Conventional analysis for reconstructing vehicle collisions has always been reliant on physical evidence, both from the incident site and from the vehicles involved. Damage sustained by the vehicles can be used to orient the vehicles relative to each other, and the markings on the roadway (i.e. gouges) can be used to place the vehicles at the point of impact. Analysis using physics can be completed to determine impact speeds and the severity of the collision, and any tire marks leading up to the point of impact can be used to assess vehicles’ travel path and the pre-braking travel speed.

However, there are gaps in the physical evidence that need to be addressed. Tire marks may show when the tires were locked up and skidding, but they may not provide insight as to when the brakes were initially applied or when the throttle was initially released. If the driver only partially applied the brakes, or the ABS system on the vehicle prevented the tires from skidding, then tire marks may not be deposited. In the past, assumptions would be made to fill in the gaps, now EDRs provide the missing pieces.

Early EDR modules reported the collision severity (delta-V) and the speed of the vehicle leading up to the collision, which was very useful since a large portion of the conventional analysis done was to determine these values. Knowing the vehicle speed filled in the gap as to where the vehicle was seconds leading up to the collision without relying on the presence of tire marks and other road evidence, or based on assumed acceleration/deceleration rates.

Additional data in EDRs now includes throttle application, brake status (On/Off), and steering wheel angle. Throttle application, and specifically the release of the throttle, can show a driver’s initial reaction to a hazard (i.e. the foot being lifted off the gas pedal).  Brakes On or Off fills the gap as to when the brakes are first applied to when tire marks are first seen, or if no marks are present, it can confirm whether brakes were applied at all. Steering wheel angle identifies another type of driver response. In the past, this information would have been based on the orientation of the vehicle at impact. If the vehicle was angled it could be consistent with steering in that direction. However, in the scenarios where a driver steers in one direction and then alters the reaction and steers in the other direction, the presence of a steer maneuver may be lost, and certainly the complexity of that steer maneuver would not have been captured.

Newer EDR modules now include multi-directional accelerometers that provide pre-impact data. This data can provide precise insight into how the vehicle responded to the driver’s input:

-    How hard were the brakes being applied and what deceleration rate was the vehicle achieving? How slippery was the roadway?

-    At what rate did the vehicle accelerate from a stop?

-    How much did the vehicle’s direction change during the steer maneuver and how far did the vehicle move laterally?

EDR data can be used to identify the location of a vehicle leading up to the point of impact. As well, this data can be used to determine when each vehicle would have become visible to other drivers, and assess driver reaction. Not surprisingly, this increased data has led to a greater scrutiny of a driver’s actions and timing.

No longer are the limits of what can be determined based on what can be observed at the scene. As the data in the vehicle EDRs continue to increase so does the clarity in the moments leading up to the impact, and with that clarity more and more questions can be asked and answered.

Written by Paul Gullekson


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