What is "good" when it comes to GPS tracking of speed? In previous employment they had eroad and also in-cab cameras, the drivers became so obsessed with not getting in trouble they tended to look at the eroad screen to manage the speed, and at the same time camera footage showed that this distracted them from looking at the road for a considerable part of the day.
My point is these pieces of equipment are tools, but businesses are using them to punish drivers, it is not that they are exceeding the speed limit but what motivates them to do it. Are they under pressure to get jobs completed, are they rushing back to base? Once you understand the motivation you can do something about it.