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What Is a Car Black Box? 5 Things You Should Know

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Introduction

Forensic engineering and accident investigation is a diverse and comprehensive field that involves the examination and analysis of both physical and electronic evidence. An integral part of the accident investigation process is the assessment of a vehicle’s event data recorder (EDR), colloquially referred to as the vehicle’s “black box.” The black box is an extremely durable electronic device capable of recording valuable information in the moments (typically five seconds) before a collision.

The concept of a black box is well-known and has long been part of the aviation industry, but many are unaware of its presence and role in the automotive industry and in car accident reconstruction. While the purpose and operating principle are similar, there are some key differences between vehicle and aircraft black boxes.

A Car’s Black Box Is Different from an Aircraft’s Black Box

Although they share the same name, a vehicle’s black box is not the same as an aircraft’s black box. In a commercial aircraft, the black box comprises two separate devices, the flight data recorder (FDR) and the cockpit voice recorder (CVR), which often combine to form a single unit. [1] The Federal Aviation Authority (FAA) mandates that that FDR monitors a minimum of 88 parameters including:

  • Time
  • Altitude
  • Airspeed
  • Heading
  • Pilot input
  • Pitch, roll, and yaw angles

By the same mandate, the CVR is required to record four channels of cockpit audio data for a minimum duration of two hours. [2] Despite the extensive data collection, an aircraft black box does not perform any safety function; it is simply there to record flight data and serve as a crash-survival memory unit.

A car’s black box (EDR), on the other hand, stores data to flash memory typically in the vehicle’s airbag control module (ACM). The ACM is a generic name for the control module responsible for airbags (primary) and supplemental restraint systems, such as seatbelts. Each vehicle manufacturer typically uses a different name for their ACM. For example, the ACM in Fiat-Chrysler (FCA) vehicles is called the occupant restraint controller (ORC), while in General Motors (GM) vehicles, it is known as the sensing diagnostic module (SDM). The primary function of the ACM is to sense a developing collision, determine if any safety devices need to be deployed, and deploy any necessary devices accordingly. Crash data recording is a secondary function of the ACM.

The crash data recording of a car’s EDR is like the aircraft FDR in that it records valuable information about the vehicle in the moments before a collision; however, the amount of the data that is recorded is not as extensive. Furthermore, a car’s black box does not record any audio such as in the case of the aircraft’s CVR. While the automotive black box does not record as much data as the aircraft black box, it is still capable of recording an abundance of data.

The Black Box Records an Abundance of Data

EDRs have been voluntarily installed by many vehicle manufacturers since 2002; however, the specifics of the data recorded (amount and type of data) vary depending on the manufacturer. In 2006, regulations were introduced (“The Part 563 Rule”) which specified the 15 minimum parameters that must be recorded should the manufacturer decide to install an EDR in their vehicle. [3] These parameters include:

  • Lateral and longitudinal delta-V (speed change) [4]
  • Vehicle indicated speed
  • Engine throttle percentage
  • Brake status (on/off)
  • Ignition cycles, crash
  • Ignition cycles, download
  • Safety belt status, driver

In addition to the required data, The Part 563 Rule also set standards for 30 other data types if manufacturers voluntarily configured their EDRs to record them. For example, if a manufacturer configured their EDR to record steering input or anti-lock braking system (ABS) activity, it would have to record five seconds of data sampled twice per second. Other optional parameters include lateral and longitudinal acceleration, engine RPM, and vehicle roll angle, among others.

A Car’s Black Box Is Not Always Black

Contrary to its colloquial name, many black boxes are not actually black. This is especially true in aviation, where the exterior of the black box is required to be coated with a heat and corrosion resistant orange paint for high visibility. [5]

In contrast, automotive black boxes do not have regulations set regarding the colour of their exterior. Although some are black, such as some BMW advanced crash safety modules (ACSM), many are silver.

Not All Black Boxes Can Be Downloaded

This is partially true. In December 2012, the National Highway Traffic Safety Administration (NHTSA) published a notice of proposed rule making (NPRM) that proposed a new Federal Motor Vehicle Safety Standard (FMVSS) mandating that all vehicle manufacturers must install Part 563 compliant EDR modules in all their vehicles. [6] The Part 563 rule further mandates that vehicle manufacturers must ensure by licensing agreement or by other means that a tool(s) is commercially available that is capable of accessing and retrieving the data stored in the EDR.

Accordingly, most vehicle manufacturers have licensing agreements with the most popular Bosch Crash Data Retrieval (CDR) tool. However, certain vehicle manufacturers such as Hyundai, Kia, and Tesla are supported by other EDR tools and are not compatible with the more common Bosch CDR tool. Consequently, when such vehicles are involved in a collision and require a black box download, the appropriate tool must be available, or the download will not be possible. Additionally, for vehicles manufactured outside of North America, the Part 563 rule does not apply, and there is no guarantee that their black box can be downloaded. In those cases, an EDR download would only be possible by shipping the ACM to the vehicle manufacturer for an in-house download.

When Airbags Are Replaced, the Black Box Is Also Replaced

When airbags are deployed, they are not repaired or repacked; they are replaced. Typically, when this is done, the ACM is also replaced. During a collision with airbag deployment, the ACM will store all the valuable crash related data and will “lock” the data so it cannot be erased or overwritten. Accordingly, a new ACM is required when replacing airbags. However, some auto shops will reset and/or reprogram the ACM in order to reuse the module rather than replacing it as it can still function as a safety deployment device.

Acknowledgments

We would like to thank Keegan Monteiro for providing insight and expertise that greatly assisted this research.

Keegan Monteiro is a Forensic Engineering Specialist in J.S. Held's Accident Reconstruction Practice. Keegan has been an active member in forensic engineering and accident reconstruction since 2021 and specializes in motor vehicle accident reconstruction, which includes speed calculations, area of impact determination, driver perception-response and behavior evaluation, vehicle crush measurements, crash data retrieval, collision dynamics, infotainment and telematics data acquisition and analysis, vehicle damage analysis, and accident site surveys. Keegan is also well-versed in vehicle mechanical assessments and failure analysis, including the examination of failed components, vehicle and mechanical component assessment, and analysis of fractured surfaces.

Keegan can be reached at [email protected] or +1 416 977 0009.

References

[1] Federal Aviation Administration, 14 C.F.R § 91.609 – Flight data and cockpit voice recorders (2013)

[2] Federal Aviation Administration, 14 C.F.R § 135.152 – Flight data and cockpit voice recorders (2016)

[3] Federal Aviation Administration, 49 C.F.R § 563.6 – 563.9 (2006)

[4] Speed change is the difference between a vehicle’s speed immediately after and immediately prior to impact. Collision severity is directly proportional to this speed change.

[5] Federal Aviation Administration, 14 C.F.R § 21.611(b) – TSO-C124b (2007)

[6] NPRM “Federal Motor Vehicle Safety Standards; Event Data Recorders,” RIN 2127-AK86 (77 FR 74144) (December 2012)

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This publication is for educational and general information purposes only. It may contain errors and is provided as is. It is not intended as specific advice, legal, or otherwise. Opinions and views are not necessarily those of J.S. Held or its affiliates and it should not be presumed that J.S. Held subscribes to any particular method, interpretation, or analysis merely because it appears in this publication. We disclaim any representation and/or warranty regarding the accuracy, timeliness, quality, or applicability of any of the contents. You should not act, or fail to act, in reliance on this publication and we disclaim all liability in respect to such actions or failure to act. We assume no responsibility for information contained in this publication and disclaim all liability and damages in respect to such information. This publication is not a substitute for competent legal advice. The content herein may be updated or otherwise modified without notice.

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