How are overspeed events generated from the AVL (not real road overspeed)

Owned by Amy Mackay (Unlicensed)
Last updated: 16 Dec, 2024 by Sarah Masefield
2 min read

To see how real (posted) road speed events are generated, see this article - How are Posted (Real) Road Speed overspeed events generated

The overspeed threshold

Each individual Smartrak GPS unit is capable of being configured with a single overspeed threshold. When the speed of the GPS unit exceeds this threshold for 10 seconds, the unit is considered to be speeding, and an overspeed event is generated.


For fleets that travel on the open road, the overspeed threshold is typically set between 101 and 110km/hr, slightly above the typical open road speed limit of 100km/hr.


For slower-moving fleets (such as diggers, mowers, or heavy machinery), the overspeed threshold can instead be set to the maximum safe operating speed of the vehicle.
 

It is important to note that since the GPS unit can only be configured with a single threshold, detection of speeding based on the posted speed limit of the road is not possible at this stage.

*for New Zealand customers Smartrak has implemented an update to account for the two roads which recently had speed limits upgraded to 110km/h.



Overspeed accuracy and filtering

The nature of GPS positioning means that given certain circumstances, the GPS position and associated speed reported by GPS may be incorrect beyond the normal accepted range.

Such inaccuracies are predominantly caused by the GPS antenna being partially or fully occluded from the sky, such as around mountainous terrain and high-rise buildings, or in underground environments.

These inaccuracies can lead to the reporting of false-positive overspeed events.


To minimise the effect of these environments, the following measures are taken:

  • The GPS position must be of sufficient quality, obtained from, at minimum, 4 satellites.

  • The GPS speed will be invalidated (Not Used, shown as 0 km/hr) for the next 2-5 seconds if it fails one of the following validations:

    • The GPS speed has not increased or decreased by more than 20km/hr within the last second.

    • The GPS speed is within +/- 9km/hr of the calculated point-to-point speed, given the previous and current position.

  • The GPS speed must remain above the threshold for 10 samples (1 second per sample) before an overspeed event is generated.

 

Overspeed Duration configuration, the following also applies:

  • A Below Speed event will be generated when the GPS speed falls below the threshold, or the current speed becomes invalidated.

  • An additional overspeed event will be generated roughly every 5 seconds while the GPS speed remains above the threshold.