Car and light truck black boxes or Event Data Recorders (EDRs), were originally developed to assist car manufacturers and airbag systems manufacturers to control airbag deployment and to collect data at or about airbag deployment. It helped the manufacturers tune the airbag systems.
In the National Transportation Safety Board’s (NTSB) list of their Top Ten Most Wanted Safety Improvements for 2017, they listed: Expand Recorder Use to Enhance Safety. In this item, the NTSB noted that the modules were widely implemented in passenger vehicles and light trucks. These devices are generally referred to as Event Data Recorders (EDR) in passenger vehicles. They are also known as Airbag Control Module (ACM)
However, the NTSB wanted these types of devices implemented in all major forms of transportation. In commercial motor vehicles (CMV) these devices are referred to as Engine Control Units (ECU) and Engine Control Modules (ECM). In addition, these types of devices are also in freight and passenger trains.
The volume of information recorded by EDRs is ever increasing. The analysis of the data can certainly increase vehicle safety as the data is aggregated and acted upon. However, it is can be important to collect the data for litigation purposes.
The data from EDRs is collected post-crash. The data is then analyzed to help determine the status of the vehicle prior to the deployment of the airbag and for a few seconds after deployment of the airbag.
Different manufacturers record different information in their Airbag Control Modules (ACM). The most common data elements collected are: whether or not the brakes were active, the speed of the vehicle at the time of impact, how far the accelerator was depressed usually expressed as a %, the engine revolutions per minute (RPM), the steering angle, and whether seat belts were "Buckled" or "Unbuckled" at the time of the crash.
Newer EDR systems are connected to more of the vehicle’s computer. They are constantly collecting information from the various other computers in the vehicle. EDRs are usually integrated with the Supplemental Restraint System (SRS). SRSs include the sensors that can detect impact or sudden deceleration and determine what passenger restraint systems to deploy such as Airbags or Seatbelt pretensioners.
As these modules become more sophisticated the amount of data collected increases. Newer EDRs collect information about the direction of the car’s movement including Longitudinal (Front to Back) and Lateral (Left to Right) Acceleration and Velocity change as well as Vertical (Up and Down) Acceleration and Roll Rates (Roll Over). These data points can be incredibly helpful in reconstructing the crash.
The data downloaded from older EDRs usually contains just a few pages of information. It is not uncommon for newer EDRs to have dozens of pages of data to report. Each system is different and each vehicle can have different systems that are being monitored by the EDR. Ultimately, the amount of data reported is dependent upon the make/model/year of the vehicle being evaluated. EDRs are designed to be tamper-proof. The data collected is written to non-volatile memory* which can store the data without any power. Transmission of data from vehicles also happens.
General Motors' OnStar system currently transmits airbag deployment information along with the location of the vehicle in GPS coordinates. This transmission happens as long as the vehicle has cell phone coverage. Teslas are constantly transmitting data via a cell phone signal to servers that are believed to be in California via a cell phone device built into the vehicle.
