I too have an '05 HCH that I purchased new in Southern Indiana .
There, in flatter terrain and slower highway speeds (55mph), the mpg was averaging about 42mpg.
Here, in San Diego, with the rather hilly terrain, significantly higher highway speeds (avg 65-75 mph
), and the state mandated fuel additives, the car averages about 35mpg.
With great care and attention, limiting top hwy speed to 65mph, limiting passengers to 1 (3-4 people in the car drops mpg down to about 30mpg), I can get 37-38mpg.
My fear is though that the hilly terrain is taking its toll on my AMA BAttery causing it to be in charge mode much too often which really hits my mpg hard! The Elec. Motor Assist is used a lot every time I climb small hill, and runs the battery down. So on even flat terrain, I'm having to recharge the AMA Battery.
I've come to the conclusion that the hybrids are excellent for flatter terrain and single drivers, but beyond that, they are not designed to deal with heavier passenger loads and moderate to difficult terrain. I'd be just as well off driving a Toyota Matrix/Pontiac Vibe like my youngest daughter which averages 31mpg in the same terrain at significantly cheaper purchase price and no worries about a the failure of a very expensive battery component, or even my other daughter's Mini-Cooper which averages 35 hwy, 29 city (but runs premium gas..ouch!).
I'm considering selling my HCH before the AMA Battery fails to avoid the hassle. Like I said, I fear that it's nearing that point already at just 50K miles. I'll buy a compact as my wife's daily commuter.
Good luck with your HCH.
I'm amazed at the reported avg mileage for the HCH (avg 46 mpg). There's no way I can come even close to that here in San Diego.