Overhead lines have a range of advantages that usually make them the default option for transmission system operators: the technology is well-known and reliable; they are easy to build and access for maintenance purposes; there is ample insight in building and operating costs that currently are estimated to be lower than those of building a cable. Cables, on the other hand, entail a reduced visual impact, which is an important argument for affected populations and local communities. Yet, laying underground cables usually requires state-of-the-art technologies and higher installation costs.
The major environmental impacts of overhead lines occur when they are already in operation. They are mainly related to birds colliding with the lines as well as the visible effects on the landscape. For underground cables, it is the installation that turns out to have the most significant ecological impacts. Trenches need to be excavated and access to the construction site has to be cleared for heavy machinery needed for cable transportation and trenching. Construction works affects the ecosystem and may also cause soil compaction, which in turn can have considerable negative impacts on biodiversity. Electromagnetic fields are believed to be less of an issue with cables.
RGI aims to: determine how to evaluate the options of overhead lines vs. cables in specific natural settings; give recommendations on relevant criteria to look into; explain the choice of cables vs. overhead-lines to a concerned public.