The average mph must be based on the time of the trip rather than the average speed when the car is in motion. OK. That is fine. I guess I could calculate it myself fairly easily, if I needed it. But why do I want this information? How is it helpful or useful? What does it tell me about driving the Prius?
You really couldn't calculate it. The influence of driving slow and being stopped with the system still active is more than you think. After a few months, you'll likely start to see a pattern emerge. It's a "big picture" data element most people simply never gave any thought about... until they're sitting there at the stoplight with the Heater or A/C running and the engine off. Pure highway cruising can be eye-opening too. Reset one of the meters from time to time. It's quite interesting to watch the correlation between MPG and that average MPH. .
I have be unable to find any value in the MPH display. My old Garmin has a similar feature, and I paid very little attention to it as well. Maybe on a day long trip it might be mildly interesting to see what the average speed has been for the day, but on stop and go, in town, fill-up once a week travel ..... I am not interested.
It's your overall travel speed for a given distance, including the stops and slowdown. It's a single number that equates to the variable speeds during the trip. It's gee wiz knowledge. It's why we were all late for dinner at Mom's. The traffic you didn't anticipate lowered you average MPH . Sometimes it's a indicator we should have taken a bike. Or how inefficient this whole car thing is, and possibly how speeding gains little.
