Steve Jones, independent GIS logistics consultant, introduces the core map data used for routing in his recent articile « Introduction to Road Data » appeared in Directions Magaszine.
Part 1 of the his article covers road network accuracy, network connectivity and road speeds, hierarchical routing, and road classification.
Part 2 of the article gets into the details of using a road network for routing vehicles. He discusses how road speeds and impedances are applied, and addresses the use of traffic data (historical and current).