The issue
Transmission lines often face obstacles in the siting process because they consume lengthy stretches of land – known as rights-of-way – and many people would prefer to access their 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. Some industry observers would suggest that transmission lines should routinely be buried underground, like natural gas pipelines, to eliminate the problem.

The pros and cons of undergrounding
It is true that once transmission lines are buried, they are out of sight. This can ease the challenges of siting major transmission projects. Ice or wind storms will not be likely to result in customer outages.

Miles of U.S. Transmission Line
Source: Edison Electric Institute

However, policymakers should be aware of the complications also caused by undergrounding. First, at a minimum, underground transmission projects cost 2-3 times equivalent overhead projects. For a 138-kV line, this translates to a $1.5-2 million premium per mile of single circuit line. Cost differences can be as great as 5-10 times when traveling through particularly challenging geographic regions – certain soil and rock formations, mountains, urban areas and protected wetland habitats, to name a few.

When an underground line endures some kind of fault, the outage typically is longer because the cable must be sectionalized and tested to find the fault – it cannot be isolated as easily as an overhead line.

From an environmental standpoint, all vegetation must be permanently cleared in the line’s path, to provide access. Such cables are embedded in oil insulators that require shunt reactor stations every few miles. And construction through fragile habitats is much more disruptive than that needed for overhead lines.

While none of these concerns should be “deal breakers,” they definitely need to be cautiously considered. Especially regulated utilities should exercise discretion in considering underground lines – proving their costs are “just and reasonable” to a state utility commission can be challenging when the cost differentials are so steep.

Average U.S. Cost Per Mile: New Transmission Construction (in millions of dollars)

AEP position
AEP does not question the occasional benefits of undergrounding lines. But the price differential of underground vs. overhead makes for a challenging cost-benefit analysis.

It is AEP’s position that a regulated utility should consider underground lines as a method of last resort, leaving the costlier technologies to merchant proposals.

AEP undergrounding cost experience
These are some examples of undergrounding proposals handled by AEP.

The City of Roanoke, Virginia
AEP was requested by the City of Roanoke to relocate approximately 3,200 feet of double-circuit 69-kV transmission line with a double-circuit 12-kV under-build. The city was responsible for 100% of undergrounding costs: about $2 million.

South Padre Island, Texas
A request was made to reconstruct an existing 138-kV 6.8 mile overhead line across the Laguna Madre with submerged cable. The request was part of a term easement renewal. Replacement of the overhead line was estimated at $500,000 (2002 dollars). The equivalent submersible option was estimated at $10 million and the submersion option was abandoned.

Undergrounding (PDF)