Underground Lines
Why not build transmission lines underground?

Underground transmission lines are extremely costly to build and repair. Underground lines cost at least twice as much as overhead lines and, depending on terrain, environmental constraints and other factors, can cost up to 10 times as much to build.

Regarding reliability, a problem with an underground line can take a week or more to locate and repair, compared to just hours for overhead lines. While underground lines are less susceptible to storm-related outages, overhead transmission lines are also rarely subject to weather-related outages. It is overhead distribution lines -- the lines that service individual homes and businesses -- and not transmission lines, that typically experience weather-related outages.

Underground transmission lines require a cleared easement, the installation of large, above-ground structures at every line termination and the construction of numerous access vaults.

In addition, the environmental impact of digging trenches to bury cable is significant when contrasted with above-ground construction.

Underground transmission lines require a concrete-lined trench and truck-sized splicing vaults.