Black Box Analysis
Event data recorders (EDRs), sometimes referred to as “black box”, are installed in over 95% of the passenger vehicle manufactured today and can store valuable data regarding what a vehicle did before, during, and after a collision. EDRs are part of a vehicle’s airbag control module (ACM) or powertrain control module (PCM) and the data it stored can be retrieved from select passenger vehicles dating as fast back as 1994. Below shows a timeline of EDR coverage, or when data retrieval was first available for specific manufacturers using commercial tools.
EDR data may include information about vehicle speed, speed change (delta-V), brake status, throttle position, engine RPM, airbag deployment status, occupant presence, and seatbelt usage. Newer vehicles are capable of storing additional information such as oil pressure, seat position, yaw rate, transmission shift position, steering input, cruise control status, ABS status, and more. Depending on the vehicle manufacturer and model year, pre-crash data can be available for around 2.5 to 25 seconds (most often 5 seconds) leading up to the collision event in intervals of 0.5 or 1 second. The pre-crash data can provide a timeline of driver actions leading up to the collision, and in some cases, can assist experts in identifying contributing factors of a collision. NBI’s experts are qualified to retrieve, analyze, and interpret the data downloaded from the “black box” of vehicles.
While Event Data Recorders provide crash-related information and can be a powerful tool in assisting the determination of liability in a motor vehicle collision, it cannot be applied without understanding the limitations associated with the the data collected and the recording criteria. For example, the EDR-reported speed is measured by sensors monitoring the average speed at the drive wheels. Therefore, the EDR-reported speed can be underreported in cases when the subject vehicle is in yaw. In addition, studies have shown some discrepancies between the EDR-reported speed change and measured speed change in instrumented vehicle tests. Generally, EDR data should be treated as a source of physical evidence and as a supplement tool to corroborate a thorough accident reconstruction.
Newer generation Toyota/Lexus/Scion vehicles (2013 to present) may be equipped with vehicle control history (VCH), a special type of event data recorder (EDR) that collects data by monitoring for certain triggers related to vehicle systems and driver inputs. A crash event is not required to trigger a VCH event. The VCH triggers based on system-related events (lane departure, pre-collision braking, or ABS activation) and driver-related events (sudden braking, sudden steering, sudden acceleration). The VCH stores data such vehicle speed, engine RPM, throttle opening, acceleration, and steering for 5 seconds prior to an event and 5 seconds after an event. For each event, the associated ignition cycle, date and timestamp according to the GPS system, event triggered, and odometer are recorded.
Commercial motor vehicles (CMV), including trucks and tractor-trailers, do not have airbag modules or crash-sensors like passenger vehicles do, but continuously records data that may capture a collision event. Events can be triggered by a “last stop” event, or by a meeting a threshold change in velocity over a period of time that qualifies as a “hard braking” or “sudden deceleration” event. Data is stored in the engine’s Electronic Control Module (ECM) that controls the engine performance, power generation system, and emission system. The ECM records parameters such as vehicle speed, engine speed, engine load, accelerator/throttle position, brake application, engine RPM, clutch status, and diagnostic codes for up to 1 minute 44 seconds before a “trigger event” and 15 seconds after.
Which commercial vehicles can be downloaded? The availability of EDR data in commercial motor vehicles is dependent on the engine manufacturer rather than the truck manufacturer. NBI experts can obtain HVEDR (heavy vehicle event data recorder) data from the following engine manufacturers, with each manufacturer requiring distinct hardware and software:
- Detroit Diesel
Some commercial vehicles can only store 2 sudden deceleration events before being overwritten by newer events, and some commercial vehicles record data in a buffer such that when the engine is re-started after a collision, the data is lost. Due to the time-sensitive nature of heavy truck data, it is important to set up a vehicle inspection with our experts as soon as possible in order to preserve the data. Similar to passenger event data recorders, the data obtained from heavy trucks should be analyzed by an accident reconstruction expert to identify the onset of a collision within the hard-braking event.