A few months ago I bought a Toyota Camry that has a fuel saving system called "Eco." I had watched as the Eco light would go on and off depending on how I drove. When I accelerated quickly the light would go off and then come on when I reached my desired speed. The rate at which I accelerated determined how long the light would go off. So I decided to try an experiment and turn the Eco light off and drive for 100 miles with the light off. I can tell the average gas mileage that I got during that time on my dash. I averaged 23.1 miles a gallon driving normally with the light off. Next I reset the trip computer and turned back on the Eco light. Trying to keep the Eco light on as much as possible I wanted to see what my average gas mileage would be. Accelerating slowly, maintaining a constant speed and slowing down when I approached a red light I found I could keep the Eco light on about 95% of the time. I couldn't help but notice how often other drivers would try and pass me when I accelerated at a slower pace. I usually caught back up to them waiting for the next red light. Average mileage per gallon this time was 29.7 miles a gallon. A 29% savings in gas usage.
So when I filled up at $1.93 a gallon and saving 10 cents by using my credit card that gives me 5% cash back I was at $1.83 a gallon. By using the Eco light I saved another 53 cents (29% less gas used a gallon) a gallon bringing down the cost of a gallon of gas to $1.30.
Of course this whole discussion on what a gallon of gas costs is mostly related to the type of vehicle we drive and how we drive. Drive a Prius and you pay a fraction of what you pay per gallon to drive a Toyota Tundra truck or a GM Denali. I am always amazed when I see a GM Denali with only one person in the vehicle. Talk about overkill.