I do agree that these is not a huge saving for fuel, as you have to fuel your body more. However, don't forget the costs of owning and maintaining vehicle.
I wonder how much it costs to maintain a bike versus a car per mile. $30 for 2 tires every 2500 miles would cost about $256 dollars to go 40,000 miles. A $250 set of small car tires should last for more than 40,000 miles. A car needs a $20 oil change every 3000 miles or so, but would you use more than 4 $5 bottles of lube to ride a bicycle that far, especially in adverse condidtions. Also on a bike you need special clothes that always need washed and eventually wear out and need replaced. Then there's brakes, cables, bearings, pedals and everything else that needs maintained. Bike parts are cheaper than car parts, but they last far, far fewer miles. I'm guessing that including fuel and maintenance a bicycle is not really cheaper to operate per mile than a small automobile.