Accident Reconstruction with Telematics Data: Quick Guide for Fleet Managers

Article Published by Geotab
Author: Siam Ahmed, Technical Services Engineer

What Is Accident Reconstruction?

Accident reconstruction with telematics is the process of using telematics data to understand the events that occurred before, during, and after a collision.

Telematics data is highly valuable because it provides an accurate, scientific record of events. It allows you to go beyond word-of-mouth testimony. The granularity of the data can tell you many things about the accident. Telematics makes it possible to gain a broader perspective by looking at the historical patterns for a specific driver or vehicle.

MyGeotab offers access to a number of different types of data that are critical to accident reconstruction, including the Trips History, Accident and Log Data, Speed Profile, and the Accelerometer and RPM graphs.  By reviewing and analyzing this data, you can verify the events of the accident.
Telematics data for accident reconstruction

This post provides an overview of accident reconstruction, including:

  • Key reports to review and where to find them in MyGeotab.
  • How to view the accident on the map.
  • How to interpret the data, as shown by step-by-step explanations of two real case examples.

Note: For legal purposes or court cases, properly trained engineering or physics experts should be consulted.

Reviewing Accident Data in MyGeotab

Key Reports

The following reports in MyGeotab provide information about what happened before, during, and after the collision. Click on any of the images below to enlarge.

Map & Trips History — The Map shows you the date, time, and location of the event and provides contextual information about the event, such as whether it occurred at an intersection or parking lot. Toggle the view to Satellite for more detail.

Telematics data for accident reconstruction

Accidents & Log Data — Provides a useful, graphical representation of the engine data and acceleration. To access, go to Engine & Maintenance > Engine and Device > Measurements.
Speed Profile in MyGeotab

Speed Profile — See a real-time graph of the speed of the vehicle. Go to Activity > Speed Profile.
Speed Profile in MyGeotab

Accelerometer Graph — Provides a useful, graphical representation of the engine data and acceleration. To access, go to Engine & Maintenance > Engine and Device > Measurements.
Engine Data Profile in MyGeotab

RPM Graph — To access, click on Engine & Maintenance > Engine and Device > Measurements. Select the vehicle and time, then click on the red graph beside Engine speed.
RPM graph in MyGeotab

Exceptions Report — The Exceptions page provides a summary of all exception rules that have been broken within a specific time period. It is important to consult the Exceptions report if acceleration rules are involved, or if you’re working in an industry where there is an auxillary set up, or diagnostic trouble codes (DTC) coming through the engine.

If you already have a rule set up in MyGeotab that defines right and wrong driving behavior, then you can use those exceptions to provide more information about the accident. To find this info, go to Rules & Groups > Exceptions.

Accident Detection

Accidents are detected by the Geotab GO device upon any acceleration greater than or equal to 2.5 g where 9.81 m/s2 is the acceleration due to the Earth’s gravity. The firmware will not use accelerometer Up/Down (aka Z axis) in this calculation. The calculation uses the magnitude of the hypotenuse between X and Y (√(X2+Y2)) Where X is Forward/Braking and Y is Side to Side.

When the Geotab GO device detects a 2.5 g event in any direction, the device is triggered to start recording at 100 Hz frequency. This detailed, granular information will be reflected in the trip.

Possible Accident Rule
MyGeotab has a base rule in the system called Possible Accident. This rule is triggered if the accelerometer detects a change in speed of more than 25 kmph or 15 mph in 1 second in any direction. If possible, the device will send detailed forensic information about position, speed,and acceleration of the vehicle.

When the rule is set to On, a notification is sent to a user when a possible accident is detected. Event if the Possible Accident rule is not enabled, you can still see details in the Log Details and Accidents report.

Note: False alarms are possible. Knocking the device can trigger the rule accidentally, so installing the device out of the driver’s way is recommended.

Non Accident-Level Events
Sometimes an accident occurs where the accelerometer reading is less the 2.5 g. For example, in a low speed collision where both vehicles continued driving after or a slight rear end collision, an accident-level event might not be triggered. However, in these circumstances the data is still very important and helpful as accelerometer data is coming through at 100 Hz. The data is event-driven, so as there are more changes in direction or speed, there are more updates, resulting in a greater than normal number of logs.

Data Accuracy

GPS coordinates are accurate to 2.5 m in any direction. Speed is accurate to 0.52 m/s. Geotab’s curve logic polls acceleration at a 300 Hz error rate and upon detection of an accident-level event, re-polls at a rate of 100 Hz.

There are many ways in which automatically generated reports can be in error. Some directly measured quantities in the report, such as acceleration, speed, and GPS location, are subject to their usual uncertainties and measurement errors. Derived quantities, such as point of impact, are also subject to potential calculation errors.

GPS: Accurate to 2.5 m.
Speed: Accurate to 0.52 m/s.
Curve logic: Polls at a 300 Hz error rate and upon detection re-polls at a rate of 100 Hz.

First Steps


Prior to performing an accident analysis using data from Geotab GO device data, you should verify a number of items.

Check to ensure the following were true for the specific device:
✔  Accurate ignition detection.
✔  Valid GPS latch.
✔  Good connectivity of the SIM card based on the device log time and server upload time. You will have to contact the Geotab support team to confirm this.
✔  Accelerometer had not been disabled due to excessive logging (usually caused by a loose installation).

Sources of error for vehicle position, speed, and acceleration are dependent on the specific model of device; verify these with Geotab for your specific device.

In cases where the Geotab GO device was not rigidly attached to the OBD II connector, the initial acceleration data from the device remains correct, the reaction (or backward) acceleration will be in error due to the flexing of the harness. Additionally, the actual acceleration measured by the device may not be identical to the acceleration of the center of gravity of the vehicle depending on the location of the device relative to the center of gravity of the vehicle.

Data for Geotab GO devices are stored in secure data centers only accessible by Geotab. Always state the VIN (Vehicle Identification Number) for the vehicle Engine Control Module (ECM) data collected by the Geotab GO device.

Basic Procedure

In general, to reconstruct an accident in MyGeotab, you will carry out these steps:

  1. Look up the accident in the Trips history and view it on the Map. Record the date, time, and location. Gather information about what the vehicle was doing at the time. Note any exceptions.
  2. Review the Accidents & Log Data to pinpoint the accident-level event. Look for large g-force events. Then read up and down the log to understand what was happening before and after the accident, such as how fast the driver was going. Look for sharp acceleration or deceleration, either forward and backwards, side to side, or even up and down.
  3. Check the Engine Measurements and Accelerometer graph for more clues on the direction of impact. Read forwards and backwards around the time of the event.
  4. View the Speed Profile and RPM graph to see the speed of the vehicle before and after the accident and check for possible aggressive driving and driver reaction.

Case Examples: Reconstruction of Accident Data

For illustration purposes, Geotab has put together reconstructions of two real accidents involving passenger vehicles. 

Download the full report for two step-by-step examples of  how to use the different tools in MyGeotab to verify the circumstances of the collision.
Geotab Accident Reconstruction with telematics guide for fleet managers

The Roadmap for Future Developments

With the power of big data, we can now look at accidents at a larger scale. Geotab is taking full advantage of the technologies available to analyze driver patterns and provide more accurate information upon accidents. Predictive analytics will become an integral part of fleet safety management.

Fleets will be able to use big data to identify factors contributing to potential accidents and increasing a driver’s level of risk, such as location, weather, time of day, vehicle type, and specific driving patterns. The advanced analytics tools we are working towards will provide the exact information you need at your fingertips for analyzing point of impact and rollovers.

Additional Training:
Watch our Accident Reconstruction training video to learn more about uncovering accident data and reconstructing an accident. Available