PC*MILER Rail uses a minimum impedance routing program for computing routes. The link impedance used in route calculations is derived as distance multiplied by a cost factor, which essentially corresponds to route quality. High density mainlines are given a lower link cost, while medium density mainline, medium density branchline, and low density branchline have higher cost factors. The minimum impedance route between any two nodes (geographic locations) on our Rail Network is the sequence of links whose impedance sum is less than that of any other sequence of links.
PC*MILER Rail routes can be run in Single Route entry mode (the user specifies railroads and junctions manually) or using the AutoRouter to calculate all possible routes between locations. For interline routes calculated from the AutoRouter, junction interchange impedances are added to link impedances. The junction impedance for the forwarding and receiving railroads is based on the historic volume of traffic interchanged at that junction to/from those railroads.
Link costs and junction costs may be different for each of the PC*MILER Rail routing types. (See below.) Additionally, the link costs are adjusted to accommodate any directional routing arrangements.
All the various cost factors have been derived from extensive research using railroad timetables, maps provided by railroads, the Official Railway Guide, Official Railroad Station List, Railroad Atlas, and county maps. Trimble MAPS has updated these costs over the years to maintain a good match with current realistic routes.
PC*MILER Rail includes six different routing types:
- Practical routes simulate the most likely movements of general merchandise train traffic. Main lines are preferred to branch lines. A Practical route can sometimes be more circuitous than the shortest possible route.
- Shortest route calculations find the rail route with the least distance between the stops. For single routes, the shortest path within the railroad is determined for each segment. In the AutoRouter, the shortest path across all North American railroads is calculated, irrespective of the origin and destination railroads chosen by the user.
- Intermodal, Coal/Bulk, or Auto Racks may be used to determine the exceptional routings that these types of trains sometimes require.
- Fuel Surcharge routing is essentially a combination of the Shortest and Practical route formulas (because some railroads use Shortest mileage and some use Practical mileage when figuring their fuel surcharges). It provides mileage suitable for calculating fuel surcharges in conformance with the Surface Transportation Board ruling STB Ex Parte No. 661. See Fuel Surcharge Railroad Reference, for which railroads use Practical vs. Shortest routing.