The objective of this step is to assess the direct and secondary impacts of each proposed alternative within a habitat network for each individual target species or species group. The impact assessment requires design information for each alterative including the roadway alignment, profile, lane and right-of-way width, limit of construction, anticipated culvert and/or bridge locations, and stormwater facilities and conveyances. Operational details that assist in addressing potential impacts include changes in traffic volumes, noise levels, and estimated annual salt loads. Landscape disturbance processes that influence and maintain some habitats and species requirements suitability, such as periodic flooding, wild fire, landslides and sediment loads, can also be altered by transportation projects. In certain circumstances, project designs could influence these natural processes and result in a change to the habitat networks.
Step 1.1: Describe Impact on Individual Cores, Islands, Corridors and Connectivity
The potential direct impacts of each alternative can be quantified for each target species by overlaying the project features with the habitat network maps. Quantitative estimates of direct impacts to habitat acreages and connectivity changes (corridor impacts) can be documented for each alternative. As part of this process, opportunities for impact avoidance and minimization can be identified for further evaluation.
Methods for the assessment of secondary impacts on wildlife (habitat degradation and functional loss) are not well established, are typically based on professional opinion and agency coordination, and mostly qualitative. Methods to estimate the acreage of effect and the degree of effect will vary by species and habitat types. Determining an appropriate level of mitigation, if any, to offset secondary impacts may be difficult to quantify and require a more subjective approach. Procedures for selecting appropriate mitigation measures for secondary impacts are also poorly defined. Procedural guidance on assessing secondary impacts is provided in the NCHRP 25-25 Task 11 Indirect and Cumulative Impacts Analysis (Stanley 2006). The report includes a flow chart for assessing secondary impacts within the NEPA planning process as well as case studies.
Step 1.2: Revise Alternatives to Avoid Impacts
The objective of this step is to determine if potential impacts identified in Step 1.1 can be avoided through the alteration of the project design. The evaluation process and outcomes should be documented for each alternative. The evaluation should account for other potential impacts that may be imposed by a change in the alignment that avoids a habitat fragmentation impact, including cost considerations. Cost considerations should include potential changes that increase or decrease costs for roadway construction, residential/commercial displacements, wetland or other mitigation requirements, and other relevant items that would influence the decision for altering a proposed alignment.
Step 1.3: Identify Potential Minimization Solutions
The objective of this step is to initially identify and evaluate potential minimization steps that could reduce connectivity impacts. These initial minimization solutions would focus on improving or maintaining permeability through the transportation corridor using structural approaches such as underpasses, overpasses and crosswalks. The Wildlife and Roads website provides a complete decision guide for selecting appropriate measures to reduce wildlife-vehicle collisions that includes a variety of wildlife crossing structures. Using this reference, potential solutions can be identified, evaluated and either adopted as a means to minimize potential impacts or determined to be inappropriate for location.
Resources that provide further guidance on minimization solutions for this step include:
go to Step 2: Summarize Habitat Fragmentation Analysis Results on Project