Just trying to explain the impact to the average American family in terms of the savings. As noted --- for American families living on the edge every dollar counts -- so even ten dollars counts when trying to commute to a lower-wage job everyday while trying to cover rent, food, and other necessities.
The bigger impact -- as noted by Ricter -- is with commercial trucking and diesel costs. The price of transport impacts everything in the supply chain including the price of food in your local grocery store. The Duke economist only accounted for the direct savings for the family at the pump -- not the broader impact of fuel price savings related to transport of goods.
