Considering that a large portion of the American population is overweight, that means plenty of plump drivers are refueling more often.
utomobiles have grown heavier and larger over the years, partly because we carry more stuff, partly to accommodate new technology, and partly because occupants have grown larger.
According to one academic, we use 39 million more gallons of fuel for each pound added to the average weight of the American population, as compared to the average weight of the population in the 1960s.
Now, that doesn't mean that cars are heavier just because the population is, but that doesn't justify your second Big Mac, either.
Basic physics indicates that more energy needs to be used to haul around more weight, which means that it takes more power from the engine to overcome the extra weight of rotund drivers and passengers, thus burning more fuel. Considering that a large portion of the American population is overweight, that means plenty of plump drivers are refueling more often.
Of course, cars have gained in mass, too. It might not look like it, since the big boats of the 1960s have been replaced by autos with more-efficient packaging, but as more and more safety and technology features have been added both through government mandate and consumer demand, cars have gotten heavier. The demand for three-row seating has also been a cause for growth, and Americans do love to haul plenty of gear around, as well, and that also adds fuel-sucking weight.
Another thing to consider: research seems to show that the more car-dependent a society is, the more obese it is. So are Americans gaining weight because we're more car-dependent than we were in the '60s? Food for thought (pun intended).
Perhaps both cars and their drivers need to spend more time at the gym.