by Victoria Eyers
What is an Event Data Recorder (EDR)?
An EDR is a function of a vehicle’s Airbag Control Module (ACM), which is otherwise known as the Restraint Control Module (RCM). The ACM constantly receives data from various sensors around the car. This allows the module to decide whether the vehicle is experiencing an incident which might require the deployment of the airbag system. Where the signals received suggests there may be a need to deploy the airbags, data is recorded by the event data recorder. This is recorded in two forms, either a deployment event or a non-deployment event. A deployment event is where the airbags deploy, whereas a non-deployment event occurs when the airbag module considers there might be a need to deploy airbags, but the threshold to deploy is never reached. Low speed impacts or those with low forces are more likely to be a non-deployment event but irrespective of the event category, data may still be recorded.
What data does the EDR record?
There are some slight variations between vehicle manufacturers, but you can generally expect to find:
- Wheel speed
- Steering wheel angle
- Brakes on/off
- Accelerator pedal % input
- Seatbelt use
- Lateral and longitudinal Delta-V (change in speed)
- Roll angle
The way pre- and post-crash data is saved will vary between manufacturers, as will the number of events that can be saved, but there is usually 5 seconds of pre-crash data. If the vehicle’s airbags have deployed this is usually a good indication that crash data may have been captured. Where the airbags have not deployed, it is still worth investigating, but crash data is not a certainty.
Is it always available?
Not every collision will be severe enough for the ACM/RCM to consider activation. Sometimes this in itself is useful information for an expert; if no data has been created, it might mean an impact was less forceful than has been claimed. Pedestrian impacts, for example, might not be sufficient for data to be saved.
Download of the data is not always possible from every vehicle. From July 2022, access to EDR data became mandatory on all new vehicle models in the EU but not all vehicles are covered by the same download tools; some must be retrieved with the manufacturer’s own equipment. Toyota and Volvo vehicles have very good coverage, with Toyota data available on most vehicles produced since 2004. VW, Audi, and BMW are covered from around 2018/2019. Different tools are available, so to be sure it is best to provide the vehicle make, model, and age so our experts can check for compatibility before undertaking an inspection. At present there is extremely limited coverage for HGVs and motorcycles.
Is the data reliable?
The data recorded will be an accurate reflection of the information that is being sent from the various sensors to the RCM, but the data does require expert interpretation. Although the data is accurate, there are some instances where expert interpretation is required to obtain a reliable conclusion regarding the vehicle’s behaviour at the time of an incident. For example: speed data is taken from the wheel speed sensors. The RCM will accurately record the speed the wheel is rotating at, but that might not be the same as the actual road speed of the vehicle if the wheel is spinning or the vehicle is under heavy braking. Alternatively, if a sensor is located on a part of the vehicle that undergoes heavy deformation during an impact, it may no longer be giving reliable readings. This is where a mechanical vehicle inspection will also assist. This does not mean that the data is not accurate, but without expert interpretation it could mislead. As such, it is important that the data is analysed by an expert so it can be validated and interpreted appropriately.
Are there any pitfalls?
The EDR does not record the date or time of the event, therefore if a vehicle has been in a collision historically (even a minor one), old data relating to the previous incident may have been stored. Or, if an incident involves multiple impacts, separating the data into a coherent sequence can be complex. It is very important that an expert analyses the data to ensure the information being considered actually relates to the incident in question. Wherever possible, the expert should seek to validate the EDR data against other reconstruction methods.
Please contact us for further information or to check if a vehicle is supported.
This is the first bulletin in a series of information notes about EDR. The others in the series cover
- Using EDR data to explain Sudden Unintended Acceleration (SUA) events
- Four common collision types where EDR data illuminates causation
- How and when to cross reference EDR data with other digital data, such as CCTV analysis.