The U.S. Interstate Highway system is the dominant circulation system for people and goods in the United States, especially now with air travel sharply reduced. Now your first reaction to this map might be like mine: “duh, the virus is concentrated along the interstate highways because the highways connect the cities where most of the people live.” But that is not what this map shows. This map shows the doubling time for COVID-19 cases, not the total number of cases. The places along the interstate highways are the connected places and that’s what makes them vulnerable.