Distances are calculated by first determining which roads a vehicle will travel to get between two points and then adding up the distances over each section of road to arrive at a total mileage—similar to the manual task that one might follow if using an atlas.
Routes will “clean up” to the nearest truck-usable road on the highway or local street network. This local distance equals the short air distance between where the point is plotted on the map and the closest truck-usable road.
In the Detailed Report, which lists every route segment and interchange on a route, this distance may appear as “Local”.
To learn more about creating a route in PC*MILER, go here.