It's not really an edge case. Everyone drives on paved private property (parking lots and the like). A flat 2% mileage reduction per year is probably enough t

It's not really an edge case. Everyone drives on paved private property (parking lots and the like). A flat 2% mileage reduction per year is probably enough to cover this for the vast majority of people. So if someone drives 10,000 miles a year, you'd charge them for 9800 miles with the assumption that they drove about 200 miles on private property that year.