Our car has a little computer in the dashboard that calculates your miles-per-gallon as you drive. You can set it to calculate it in “real-time” as you drive or to compute the average mpg for each trip.
I think every car needs one of these because it’s an incentive to drive more efficiently when you can see how much fast, aggressive driving costs you. Instead of slower driving being boring, it becomes a challenge to see how high you can push the mpg, and it’s surprising how much of a difference driving style makes.
Our car’s a Jetta TDI diesel, which gets pretty good mileage no matter what, but driving style makes a big difference. I’ve been experimenting with trips I make a lot (to and from Teresa’s work, for example) and I’ve gotten a low of 38 and a high of 56 mpg (the indicator is a little off - I think the actual mpg tends to be 4-5 mpg lower) just by varying my style slightly. The key ingredients seem to be how early you shift while accelerating and how fast you go on the highway. For example, going 55 instead of 65 makes a difference of only a few miles per gallon, but jumping up to 75 or 80 really causes a significant drop in mpg.
Not that I plan on driving 55 everywhere (I can’t…no, i won’t say it), but it’s nice to have an incentive to take it easy a bit more & to actually make it fun.