I was looking at the US Dept. of Energy Freedom Car and Vehicle Technologies Program webpage on Hybrids at:
Advanced Vehicle Testing Activity: Hybrid Electric Vehicles
The graphs for Accelerated Reliability and Fleet Results showing mpg for each type of hybrid (Insight, Civic, Prius I & II) really surprised me.
On the monthly fuel economy graph, a lot of what I see makes sense. For instance the average mileage of the four HCH's they test drop dramatically in the first month--but it is May going into June in Arizona; so that probably means the drivers turned on the air conditioning.
Other results don't make sense to me. Why would the average efficiency of the Insight crater during October and November of '03? October and November of '02 are one of the high points of efficiency for the Insight. Even August has a significantly higher mpg for both '02 and '03--and this is in Arizona!
My real question relates to the overall mpg of all of the hybrids they tested. All of them seem to experience an overall decline in efficiency as time passes. Admittedly there is not a ton of data here, but it sure looks like all of their HEV's lost some efficiency over time. The HCH holds up the best, but even that seems to show a very slight decline.
This seems to directly contradict the experience reflected in our database. Looking over results for vehicles with over 10 tanks of gas listed, I see either the mpg improving or staying pretty much the same. This appears to be true across all four types of hybrids. I have also read a lot of discussion about hybrids increasing in mpg over time.
I'm really curious about what you all make of these results.