Hot answers tagged road
Right-click on your length field -> statistics -> look at the SUM field
EDIT : The default output of line density is in kilometer per square kilometer. So the output of the tool is already what you are looking for (you don't need to divide it again by the size of the circle, this is done automatically). Note that the vector-based approach from @Anggik will be more precise, however you will not have overlapping window analysis.
in my point of view, you should decide your unit area (it could be county boundary or certain grid). after that, do some geoprocessing to divide roads in each unit area. Then you calculate each of roads length in each unit area and divide with the hectarage (or km2).
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