Forest Plan Implementation
Procedures and Tools
Road Density Calculation Procedure
Road density (typically expressed as miles of road per square mile) is an important parameter to use in evaluating project effects. Existing road densities and future road densities should be computed. In addition, densities on National Forest System (NFS) lands, as well as adjacent non-NFS lands should be calculated. It is usually also important to subdivide the roads by open versus closed roads.
Existing densities on NFS lands can be calculated by using the "infra_rds" layer from the GIS library. In addition, the "all_rds" layer should be used to identify unauthorized roads. In the "all_rds" layer, only the additional roads that are not included in Infra and that have CATEGORY = E (for Existing) should be used. The routes identified in the "all_rds" layer should also be compared, where possible, with aerial photography or ground verification to verify that they actually exist.
For non-NFS lands, a GIS layer was developed for roads. This layer is named "non_nf_rds" and is described on the GIS Layers for Cumulative Effects Analysis web page.
Road densities should be calculated by VCU for watershed and fish evaluations and by WAA for wildlife evaluations. In addition to summarizing road densities for NFS and non-NFS lands, combined total road miles and road densities should be computed for all lands within the VCU or WAA combined. In addition, cumulative road densities should be calculated for NFS lands, non-NFS lands, and for all lands combined.
The step-wise process is as follows:
- Step 1: Define the area of interest (VCU(s) or WAA(s)).
- Step 2: Calculate existing road miles for NFS and non-NFS lands within the area of interest using GIS. Distinguish between open and closed roads on NFS lands by maintenance level. Assume Maintenance Level 2, 3, 4, and 5 system roads are open and all other roads (Maintenance Level 1 and unauthorized roads) are closed.
- Step 3: Calculate the square miles in the area of interest for NFS and non-NFS lands using GIS.
- Step 4: Divide road lengths (in miles) by the appropriate area (in square miles) to obtain estimates of existing road densities on NFS lands, non-NFS lands, and all lands combined for each VCU or WAA in the area of interest. Also calculate these densities for open and closed roads.
- Step 5: Calculate the future project-related road construction (open vs. closed) and estimate the future non-NFS road construction for the area of interest during the period that the project would be under development (e.g., 3 to 10 years). For non-NFS lands, use a conservatively high estimate. Add these future miles to the road miles calculated in Step 2 and recalculate road densities (as in Step 5) to obtain an estimate of future road densities after project development.
- Step 6: Finally, use the LSTA to estimate cumulative future NFS road mileage that could be built on NFS lands. Add to this, any likely state or other public transportation routes that are likely to be built across NFS lands. Then estimate the future non-NFS road construction for the area of interest over the long term, using a conservatively high estimate. See the separate Web pages on cumulative effects for more detail.