Undergrounding vs. Overhead lines

Electric utilities sometimes face obstacles in the siting process of overhead transmission lines because lengthy stretches of land – known as rights-of-way – are required for construction. Many people would prefer to receive electricity without ever seeing how it gets to their home or business. This is especially true in particularly scenic or historic areas, and in heavily populated areas. To eliminate the visual impacts of overhead transmission lines, some industry observers believe that transmission lines should routinely be buried underground.

Underground cable compared to overhead conductor

Underground cable compared to overhead conductor

The pros and cons of undergrounding

Placing transmission lines underground can ease the challenges of siting major transmission projects by eliminating visual impacts. Underground transmission lines are also less susceptible to outages caused by severe weather.

However, there are other factors policymakers should be aware of when considering the feasibility of underground transmission.

First, underground transmission projects cost many times more than the equivalent overhead project. In most instances, installing underground lines is more intrusive because of the need to cut roads and sidewalks, dig a trench, refill a trench, and repair the surface. Underground lines also must be routed to avoid gas, water and sewer lines and wetlands, all of which can add time and cost to construction.

New construction transmission cost per mile

When an underground line endures some kind of fault, the outage is usually longer because it cannot be identified and isolated as easily as an overhead line. In addition, the process to repair the cable is more time-consuming, resulting in longer outages and an increased reliability risk.

Underground lines are less efficient at carrying electricity, so they must be short or use expensive methods to improve the flow of power.

The combination of higher construction costs and maintenance and reliability problems have resulted in underground transmission representing just a small fraction (<1%) of all transmission lines.

None of these concerns rule out the use of underground transmission lines completely and there are circumstances where underground is the appropriate choice (in urban settings and near airports, for example).

However, regulated utilities are obligated to prove their costs are “just and reasonable” to a state utility commission. All factors, with cost being at the forefront, must be considered when evaluating options for transmission lines.

AEP position

AEP understands there are situations that require transmission lines be placed underground, but the higher cost of constructing, repairing and maintaining underground transmission lines effectively prohibit their routine use.

AEP will build underground transmission lines when it is the economically and technically appropriate solution. If underground lines are technically feasible and will maintain reliability, AEP will consider placing transmission lines underground when a third party absorbs the costs instead of ratepayers.