I am a rather impatient person and I used to be a rather impatient driver. I now drive more slowly (5 MPH above posted limits instead of 10+), accelerate much less quickly, and brake from a further distance (although I always had a pretty large braking distance, driving with people who don't is terrifying). All of these things because of the little meter on my dash that tells me my instantaneous fuel efficiency. The measurement is approximate for sure, but I can tell that when I floor it the number plummets, and when my speed is steady it's nice and high. And because the car keeps track of the numbers over the lifetime, there's an incentive to keep it high. People like to get high numbers, this is a manifestation of that weird drive.
Which brings me to my main point, we should put little doodads that show lifetime fuels use in all cars. That would be the best way to get people to change their driving habits to be more moderate (and hence safer) as well as save more fuel. Although I know I tend to look at the gauge too often, so maybe it'd increase distracted driving.
I'd like to see if cars that have those displays (my coworker's diesel car has one, so it's not just hybrids) tend to get above-average (for their cars) fuel mileage. Could be interesting.