Accident Detection and Reconstruction

Accident Detection

The accelerometer is used in an advanced accident detection system. The accelerometer is orientated to forward/back, left/right, up/down regardless of the installation using GPS data and movement. After installation, this takes about 15 minutes of normal driving.

The accident detection system does the following:

• Accidents are detected using 2D (horizontal) changes in velocity over 120ms. The change threshold is configurable in the settings below. Default threshold is 7km/h
• Roll overs are reported when the vehicle’s angle to the “normal” horizontal plane exceeds 60 degrees.
• Drop detection detects velocity changes in the vertical dimension.

Firmware Setup

The following device types and firmware version support accident detection and reconstruction:

Device Installation and Auto-Orientation

Simply secure the device firmly to the vehicle chassis, in any location that will not see excessive vibration, and at any convenient angle. The unit should not rattle or change orientation during driving, so try to avoid cable ties to flimsy wiring harnesses, and installs that might impact nearby objects when vibrating.

Once power is applied, the unit will begin to continuously self-calibrate. It begins from an non-calibrated state, in which the harsh driving detection is disabled, and the accident detection is in a basic mode that ignores orientation. Once the vehicle begins a trip, each time it accelerates, brakes, or turns, the unit can compare the acceleration to the GPS velocity to determine its orientation. Each manoeuvre increases the accuracy of the orientation, and when the accuracy is high enough, harsh driving and advanced accident detection are enabled. This typically takes 10 to 15 minutes of driving.

Even after the initial settling period, the unit continues to self-calibrate, so it will adjust to small changes in position. Large changes will result in a few minutes of inaccurate data (~90 minutes if the direction of 'down' has changed), while it adjusts to the new conditions. When intentionally re-orienting the unit, you can reset it to its non-calibrated state by flipping it over for a few seconds. In addition to triggering an accident event for the rollover (if configured), this resets all orientation data, disabling the harsh driving and advanced accident detection until recalibration is complete. The unit will recalibrate faster if you reset it in this way.

Accident Reconstruction

While driving, the device gets a GPS fix every second, this second by second GPS data is saved into a section of the device's flash memory. Some other fixes also occur (GPS freshens, movement checks). Every GPS fix is saved into this section of parameters, regardless of parameters. There is capacity for about 2 hours of data in the 'accident log' section of the flash. What exactly is done with this data in the event of an accident varies slightly depending on setup. 

The "Accident Logging" Parameter

There is further detail on parameters in the next section, but in terms of retrieving accident data, these parameters set the following behaviour:

Accident Logging/Roll Logging - Off (default)

• Every second by second GPS fix is logged in the accident log partition. 
• If there happens to be an accident, the device doesn't detect or log this
  
• However, if we are to query the accident data by sending a message to the device (see here - Accident Data Exports) - for the right time period, we can retrieve the data. If no data exists for the time period we set, the upload will come back empty. Note if after the accident occurs the car does another 2 hours worth of driving, the logs in question would be overwritten (oldest overwritten first). So it is worth enabling Accident Logging + Reconstruction Data in the parameters!!
• So the takeaway is if we get in fast enough, we can usually retrieve some accident data, irrespective of parameters.

Accident Logging/Roll Logging - Accident Log Reason, or Accident Log Reason + Reconstruction Data

• If a crash threshold is set, and a crash event occurs:

  • If Accident Log Reason is set, you get a GPS data point logged with the Accident log reason in the main log

  • If accident data + reconstruction is enabled, the second-by-second log is transcribed into the main log and uploaded, as soon as the accident is detected. This is 60 sec before the crash and 10 seconds after,

  • Likewise for roll events

The data is currently saved by the OEM server. Contact support to find out about retrieving it. There are also options to send the data to software platforms via OEM.

Point data can be retrieved in a CSV export and map data in an HTML map file. See this explanation.

System Parameter Setup

• Accident Logging allows 3 levels of logging. 
  • Off (default): results in no detection and automatic upload of reconstruction data.
  • Accident Log Reason: logs only the accident record and no reconstruction data.
  • Accident Log Reason & Reconstruction Data: logs the accident record and reconstruction data.
• Accident Delta-V Threshold is the magnitude of the change in 2D velocity over 120ms that will trigger an accident. The units are km/h. The default is 7km/h. This corresponds to 1.6G over the 120ms period. 
• Disable Orientation allows the advanced accelerometer features (roll detection, driver profiling, and drop detection) to be disabled.
• Disable Vertical Accident Filtering allows the drop notification to be disabled.
• Wakeup Threshold and Wakeup Count relate to the accelerometer's sensitivity to movement that will wake the device up or keep it awake. Generally, the defaults of 1 and 0 respectively should be used.

Accident/Rollover Alerts in Telematics Guru

Use the Alert Wizard under Admin -> Alerts to set up email, SMS or app-based alerts when an accident is detected. 

For more information on Alerts, see Getting Started - Alerts

I am getting a lot of false alerts, what can I do? 

While our devices are smart, they can't work miracles! If a change in velocity is registered above the set threshold, or the roll threshold is exceeded, an accident will be logged. Certain vehicle types may generate events like this regularly - particularly quad bikes, small vehicles being driven over rough roads etc. If they are regularly being jolted or being used aggressively you may get excessive accident alerts. It is a balance between ensuring that true accidents are detected, and ensuring that there are not false positives. 

If you are getting excessive accident alerts, your options are:

1. Start by increasing the Delta-V Threshold if you believe it is simply due to rough roads, or a small vehicle which may change velocity more dramatically regularly. The maximum is 11km/h change over 120ms.
2. If you have maxed out this value but still are getting false alerts, you can set it to 0 to disable accident logging, but keep Rollover alerts enabled. 
3. If you are additionally getting false rollover alerts, you will need to disable accident logging entirely - detecting accidents/rollovers by an accellerometer is not practical for the asset type in this scenario.