The next of the road modelling input files defines connectivity between vertices, provides a length of the line segment (in map units) and road cost information. This file contains 8 fields: SEGMENT, FNODE, TNODE, LENGTH, MAINTAIN, BUILD, HAUL and DIRECTION.



FNODE and TNODE refer to the vertex identification labels described in the vertex file. These end point vertices provide a rough approximation of the location of the line segment.


When you implement a road model you must load up the core road files, and you can optionally load the road shape file. If you load the road shape file, then the Map Viewer will use the shapes from the shapefile to draw the roads. If you do not load the shapefile, then the Map Viewer will draw the roads as straight lines between the starting and ending vertices. This means that the original road may be windy and curved in reality, but displayed as a straight line in the Map Viewer . Regardless of whether you use the shapefile or not, all of the cost, direction and length data are read from the core files. If you do load the shapefile, then the additional attributes from the shapefile will be present in the route and network tables.

The MAINTAIN field is defined as the cost per year ($/yr) to maintain the segment of road. The maintenance charge is assumed to cover the costs of keeping the road open (grading, culvert repair, snow plowing).

MAINTAIN costs are accrued during periods when the model selects to use the segment to transport wood. The value is a periodic cost, and is summed inot the appropriate road maintenance account. If the segment is not being used to transport wood within a planning period, no maintenance charge applies.

BUILD is the one-time cost incurred to build the segment of road. This cost would only be incurred when it was necessary to use a line segment that has not previously been used (eg. formerly inaccessible blocks accessed for the first time). After the segment is built, no further building charges apply (although maintenance costs will accumulate during periods when the road is being used). If the line segment represents an existing road it should have a build value of 0. Values for road construction costs are determined in the data preparation process(i.e. using DEM's to calibrate construction cost based on terrain). The cost represents the fee for the entire length of the road segment.

The HAUL field contains the cost (expressed as $/m3) to haul one m3 of wood over the length of the segment. This value will be multiplied by the cumulative product volume travelling over the segment on its way to a selected destination. This flexible data structure allows for reasonable hauling cost predictions to be derived from what harvest is forecast and transported on specific routes. This modelling structure correctly tallies the cumulative volume flow when tertiary and secondary segments passing volume merge on their way to the destination node.

The DIRECTION field specifies the direction of travel allowed on this road segment. A value of '1' means that products may flow from FNODE to TNODE, a value of '2' means the opposite direction, and a value of '3' means that flows are allowed in either direction. Multiple records can be added for each pair vertices. A pair of opposite direction one-way records might record differential hauling costs (cheaper to haul downhill than uphill). Several haul cost alternatives can also be represented by multiple records.

Figure 182. Multiple direction road segment

Products can flow through the road network in a variety of ways. It is even possible for loaded trucks to pass each other carrying different products to different destinations.