Tire pressure, weather (cold), and terrain has a lot to do with mileage. There are "numerous" threads on this site explaining everything. Your mileage sounds reasonable for the basic information you have given.
knudho, I drive 55-60MPH on routes 9 and 7 on my 60 or so mile commute from WV to Sterling, Va. I've got 90,000 miles on the car. I've been getting 68 to 73MPG on my way to work, 63 to 66MPG on the way home driving a little faster. The cold weather is a killer :!: During the summer I routinely get 80MPG going to work. I have my tires at 49pps and use the cardboard radiator block. Use the "Instantaneous fuel efficiency display" to see what kind of mileage you are getting under different conditions. It's really helped me. Sometimes when I have driven 25-30 miles, my mileage will only be in the 55-60 range thanks to the hills, but by the time I get to work I can usually get it up to the area of 70MPG. What highway are you driving on?
Cold doesn't mean freezing! What may be cold to the Insight for max fuel economy may not seem cold. I find that even in the 50s and 60s when I am driving at highway speeds that is cold (because of the volume of that cool air plowed over the engine). Hence, the warm air mods are the great fix. However, even with them, 65 mph and up takes a big toll.
What are the temps when you are driving? If it's regularly 60s or below, then warm air mods should really help.
Here in CA where I am it rarely gets below freezing, but it is plenty cold enough to hit the mpg figures. The cold engine start slows everything even in 40s and 50s for night temps.
Thanks everyone. My 2000 Insight is a 5 speed which I'm a novice on and I'm using it on I95 south of DC ,lots of rolling hills. It does seem to get better after 25 miles.
I'll try the radiator block and tire pressure, I'm also due for the 60K checkup. The temps have been below 60. This morning I drove in heavy rain and wind and got upper 40's. But earlier this week I kept it under 60 MPH and drafted a truck a little ways and did end up with a 61 MPG trip which is my best so far.
This is a great forum with lots of great input. Someday I hope to acheive the 60 - 75 MPG range as the norm.