A new study … has found that from 1970-2010, an increase in vehicle distance traveled in the US, coupled with a decrease in the number of occupants in the vehicles, combined to undercut the impact of advances in vehicle fuel economy during that period.
I’m willing to bet that the number of people per car would have changed regardless of the fuel savings. There are 5x the number of cars in the road in places where the car standards didn’t go up. Is that because they failed to increase the required mileage?