I diligently kept track of the true miles per gallon based on my odometer and the number of gallons I pumped into the car at each fill-up. The following are the results of this tracking so far and some of my conclusions.
At each fill-up I recorded the date, total miles on the odometer, number of gallons of gas, and price per gallon. The majority of my driving was freeway commuting to work, initially between Alameda and Fremont/Newark and later between Alameda and San Mateo.
The Civic Hybrid features a real-time MPG meter, as well as two trip meters that track number of miles driven and MPG for the current trips. I generally reset one of the trip meters pretty much whenever I started my car. In late 2004, I started regularly resetting the other when I filled up on gas and adding the reported MPG to my log.
I uploaded all this data to the website swivel.com, which generated the nice graphs you see previewed below (they're even nicer if you click through).
As an added bonus, they noticed my nice graphs and one of them is currently their featured graph, front and center on their home page. Sweet.
Estimated MPG vs. Actual
The above graph shows the actual MPG (the lower line, based on odometer and gallons of gas) as compared with the reported MPG (the higher line, based on the trip meter estimate). While they do track together, you can see that the car's real-time estimates are optimistic by generally 3-5 MPG.
Variability in MPG
There can be a big difference in MPG from fill-up to fill-up, and I think that's largely because a Civic Hybrid driver can greatly affect the MPG based on his or her driving technique. Driving fast and aggressively makes the MPG plummet. If you drive behind a tractor-trailer truck at 58 MPH, you can do very well.
The trip meter and real-time MPG gauge are great motivators. Adam, one of my co-workers when I worked in Fremont, bought a Civic Hybrid about the same time I did and we shared a similar commute. For a while we were competing to get a higher MPG on our daily commute (we were regularly getting MPGs in the mid-60s).
Unfortunately, I did not often maintain the patience to get the best bang for my gasoline buck.
Major trends in MPG
You may notice that my MPG increased over time, presumably as I learned to drive the car more efficiently (and perhaps as I broke it in?). My initial commute was a particularly flat route from Alameda to Fremont via I-880.
In May 2005, I started commuting to San Mateo which had some negative impact on my MPG. Potential culprits include climbing the incline on the San Mateo bridge, winds on the bridge, and more back-ups (stop-and-go traffic).
My overall MPG has so far been 42.97, but it is continuing to trend up over time.
MPG by month
While not dramatic, the winter months of January and December had the lowest average MPG. That could be a factor of the battery being less efficient when it is colder, or the impact of wind and rain.
I was very curious when I bought my car what the payback period might be at which the cost difference between purchasing a hybrid over a conventional car ($3000 over a standard Civic) would be paid back by gas savings (not that that is the only reason for buying a hybrid, mind you). Gas prices did go up more than I thought they would over the early lifetime of the car. This is what I paid per gallon:
Ah, remember the days of $1.50/gallon?
My previous car (a 1989 Civic Hybrid) was getting about 28 MPG when I sold it. I have so far saved about $2,900 over what I would have spent filling up a car of that efficiency.
Compared to the 31 MPG a new standard Civic would have gotten (if it actually met its claimed MPG), I would have saved $2,100 so far.
Not too bad. My next step: get my MPG numbers back up now that I've shamed myself by posting the results of my inefficient driving.