Don't get me wrong either, it'd be a nice feature to have for some, but I think you're asking for something a little different.
How about forgetting the average for that 10 min slice and say whether a road is slow on average for that road in total, like Google maps traffic layer. Is that what you mean?
That would be pretty nice. Or even a notification like a speed camera, but for a change in speed? There are easier ways to do it I suppose
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