70 cars per minute
What Is The Average Number Of Vehicles On Any Given Mile Of United States Highways At Any Given Minute?
I am a highway engineer but not a highway statistician so this is very rough information. Usually traffic counts are recorded in average volume per day and the number of vehicles is for both directions on a given highway. It would not be unusual to have a count of 100,000 vehicles on an interstate in an urban area. Ignoring rush hours etc, and just assuming the traffic is the same rate all 24 hours, 4,166 cars would pass a point each hour. It would take about one minute for those cars to go one mile so 4,166 divided by 60 would yield about 70 cars per minute. This is a very rough number based on a 100,000 per day count.
Very hard to tell, many different places are more rural than other, and also depends on the time...