How to use the filtered and unfiltered posted speed reports.
There are two versions of the 'Posted Speed Limit Events' report. You will see one that shows 'filtered' at the end and one that says 'unfiltered'.
What we found with regard to the posted speed limit events was that there were a few scenarios which could result in 'false' speeding events. The two most common are due to actual geographical overlap (vehicle travelling on an overpass and the system cannot determine whether the speed limit of the overpass versus the road underneath is the applicable limit) and GPS drift (due to normal GPS variance, the location triangulates on a close-by road with a different speed limit to the actual).
The 'filtered' report version has some additional checks built in that look at the data points before and after a speed event to filter out those that could have resulted from the above two situations. With email alerts, we cannot run the same kind of checks and the system will send an alert for every event.
What does that all mean? We recommend using a combination of those tools in monitoring speeding behaviour.