by Liia Koiv-Haus, ASLA, AICP
Visual Impact Assessments (VIAs) are a technical resource report produced for transportation projects that require consideration of the National Environmental Policy Act (NEPA). VIAs evaluate visual resources—scenic views or vistas—in a project study area and develop mitigation measures to reduce or mitigate a project’s negative impacts on visual resources. Because they require landscape design, revegetation and grading expertise, these reports are often completed by landscape architects. For example, a wildlife overpass might be designed to blend in with surrounding vegetation and topography as the result of mitigation commitments established by the VIA.
NEPA is generally required for projects involving federal lands, federal dollars, or a federal agency permit. Different federal agencies have different methods for visual assessment; the Federal Highway Administration (FHWA), US Army Corps of Engineers (USACE), Bureau of Ocean Energy Management (BOEM), Federal Energy Regulatory Commission (FERC), Natural Resources Conservation Service (NRCS), Bureau of Land Management (BLM), and United States Forest Service (USFS) all have varying requirements and guidance.
The 2015 FHWA Guidelines for the Visual Impact Assessment of Highway Projects provides nationwide guidance for Departments of Transportation (DOTs) completing VIAs. These guidelines state that “With the ever-increasing sophistication of computer modeling, adding vegetation and structures to [a] corridor’s topographic information to establish actual physical constraints will become increasingly possible and is preferred for the VIA.” The computer modeling discussed here is referred to as a “viewshed analysis.” A viewshed analysis is a computer algorithm or analysis using Geographic Information Systems (GIS) software that shows what area is visible from a certain location, taking into consideration obstructions like buildings, trees, and topography. The visible area is called a viewshed and is typically depicted on a map.