In this article, the automotive engineers at Robson Forensic provide an introduction on the capabilities and limitations of vehicle EDR (black box) data.
Automotive Event Data Recorders
The Event Data Recorder (EDR) or vehicle ‘black box’ is one of the most useful tools available to crash reconstructionists. For vehicles equipped with this technology, and when the recorders work as intended, the EDR provides crash investigators with valuable information that in many instances could not otherwise be collected. Despite the many advantages of EDRs, these systems have their shortcomings.
In this article we provide an introductory lesson on the benefits and potential pitfalls of using EDR data. We also explain some of the information that is commonly provided within EDR read-outs and some insight on when you should question the data presented.
History, Fundamentals, and Regulations of EDRs
General Motors began recording collision data to gauge real world performance of airbags and other restraint system components by recording the crash pulse. Later, GM added the ability to store vehicle parameters such as speed prior to the collision. Event data recording is typically handled by the Airbag Control Module (ACM), but in some vehicles data can be stored and retrieved from the Engine Control Module (ECM) or Powertrain Control Module (PCM). In the industry, we generally call them Event Data Recorders (EDR) - the systems concerning the collection, storage, and retrievability of onboard motor vehicle crash event data. Crash Reconstructionists and Police can often retrieve crash and/or pre-crash data with Bosch Corporation’s Crash Data Retrieval (CDR) System or manufacture specific software/hardware. Not all vehicles can be downloaded as:
- not all vehicles are compatible (non-supported OEMs, older cars)
- not all crashes trigger the recorder (rear impacts, light crashes)
- some recorders may be damaged, or lose power during a crash event
Check with a Robson Forensic expert or the Bosch Corporation to determine which vehicles can be downloaded. In general, the CDR can access some GM vehicles as old as 1994, Fords from 2001, Toyotas from 2003, Chryslers from 2006, and some Honda, Mazda, Nissan, Volvo, and Volkswagens from 2012. As of Sept. 1, 2014, all new cars, light trucks, vans and SUVs sold in the United States must be equipped with an Event Data Recorder (EDR) in accordance with 49CFR563.
The designed purpose of the EDR is to monitor data from specified sensors and record that data in the event of a collision that is of sufficient force to cause an airbag deployment. Some systems will also record events that are near the threshold for airbag deployment. In performing this task, the ACM uses integrated and remote mounted accelerometers and possibly other sensors that monitor the deceleration rate and heading of a vehicle to determine the severity of a collision and determine what, if any, passive restraint systems should be deployed. The various vehicle manufacturers (OEMs) have unique criteria used in creating the deployment threshold. Some of the crash parameters that may be recorded include:
- “x” seconds of pre-crash data
- Speed of vehicle (MPH)
- Crash severity (delta-V)
- Safety belt status
- Engine throttle %
- Accelerator pedal %
- Brake switch status
- Brake lamps status
- Cruise control status
- Yaw rate (deg/sec) (if equipped)
- Traction control button (if equipped)
- Shift gear position (if equipped)
- Seat track position (if equipped)
- Airbag Warning Lamp “On” Time Before Event (min)
- Tire pressure
Potential Problems with EDR Data
Many reconstructionists prefer to rely on EDR data to provide an unbiased measure of pre-impact actions and impact speeds. However, there are times that EDR information should not be relied upon, or requires in depth interpretation, such as when:
- The EDR data contradicts physical evidence
- The data is out of the common driving range (low or high)
- There is a discontinuity in the data (flat lines, spikes, etc.)
- Events such as multiple impacts, spins, airborne, rollover, or narrow object collisions
- The ownership of the data is disputed or the chain of evidence is suspect
When a vehicle impacts multiple objects, the timing of the recorded events can be flawed or out of sequence, as data is continually overwritten. Impacts that compromise the electrical system may yield bad data. Data in the EDR comes from multiple systems, this data can be out of sync or wrong compared to the Airbag Control Module’s timing circuit and accelerometer(s). Newer EDRs may have the ability to record more than one event.
EDR components can corrode over time. Also, data can be overwritten or plain wrong if the download is performed improperly. Collisions and vehicle maneuvers that alter the wheel speed relative to the actual vehicle speed can yield misleading data. This can occur when the vehicle goes airborne, spins, loses or locks-up a wheel, rolls over, or is cut in half. Narrow and light weight object impacts as well as small overlap collisions are often either not recorded or the data is flawed. The duration of the impact also may exceed the recording threshold of the EDR.
VEHICLE CRASH INVESTIGATIONS
Every expert in the Crash practice at Robson Forensic came to our firm after longstanding careers in the automotive industry. As automotive engineers they understand vehicle dynamics and how vehicles respond before, during, and after a crash. Our engineers, through their education and training, have a thorough understanding of physics and vehicle systems and how they affect the nuances of crash reconstruction.
To discuss your case with a subject matter expert, submit an inquiry through our website.
Steven conducts investigations involving vehicle failures and malfunctions, both as a crash reconstructionist and as a design expert. Steven’s engineering and design experience reaches nearly every mechanical and structural aspect of the vehicle. Steven has direct experience with the design and use of product durability test equipment as well as the quality assurance pro¬grams utilized by the auto industry. Steven is a member of the Society of Automotive Engineers (SAE), holds a Pennsylvania State Inspection License and has been published on Engineering Test and Analysis Methods on multiple occasions.