October 3, 2011 | 2011-R-0338
UNDERGROUNDING ELECTRIC LINES
By: Kevin McCarthy, Principal Analyst
You asked for a discussion of the benefits and costs of placing electric distribution lines underground, particularly in urban areas. You also wanted to know whether there are barriers to placing these lines underground. In practice, undergrounding typically involves telecommunications as well as electric lines. This report discusses the cost and benefits of undergrounding both types of lines, but focuses on electric lines. OLR Report 2004-R-0572 discusses issues surrounding the undergrounding of part of the Norwalk-Middletown electric transmission line.
SUMMARY
This report summarizes recent reports on undergrounding electric distribution lines prepared by public utility commissions in Florida, North Carolina, Oklahoma, and Virginia; a legislative task force in Maryland; and a national study prepared by the Edison Electric Institute (EEI), the trade group of investor-owned electric utilities. Several of the commission analyses were conducted in the wake of major outages caused by storms and, in the case of Florida and Virginia, were prepared at the direction of the state legislature.
The primary benefit of placing new or existing distribution lines underground is that it reduces the frequency of outages, particularly those caused by storms. Undergrounding reduces the costs of post-storm restoration of the electric system and reduces revenue losses for electric utilities resulting from these outages. Undergrounding substantially reduces the costs of tree trimming and other vegetation management and damages to electric facilities caused by vehicle crashes. It reduces the risk of the pubic coming in contact with live wires. In addition, undergrounding provides aesthetic benefits by reducing visual clutter. This may increase the value of nearby properties, although this issue is not analyzed in the reports summarized below.
On the other hand, undergrounding is expensive. According to EEI, building a new overhead distribution line costs between $136,000 and $197,000 per mile, depending on several factors including population density of the area served (urban areas being the most expensive). The cost of new underground lines ranges between $409,000 and $559,000 per mile. The Virginia commission estimated the cost of new underground lines to be four to six times more expensive than new overhead lines.
Undergrounding existing overhead facilities is even more expensive. The Virginia commission found that “the relocation of currently existing overhead lines would result in tremendous costs and significant disruptions… [and] could take decades to complete.” It estimated that the cost of placing all existing electric distribution lines in the state underground would be about $83 billion or about $3,000 per customer per year. Undergrounding telecommunications lines statewide would cost an additional $11 billion. The Florida, Oklahoma, and North Carolina commissions made similar findings.
We have not been able to find any general cost estimates for undergrounding in Connecticut. However, several years ago Yale University proposed to build a new biology building on Whitney Avenue in New Haven. As part of the project, the university proposed to bury the existing electric and telecommunications lines on both sides of the avenue from Edwards Street to Trumbull Street, a distance of one-half mile. The architect for the project, Pelli Clarke Pelli, estimates that undergrounding the lines in this area, which primarily serves commercial and institutional customers, would cost approximately $2 million ($4 million per mile).
There are several disadvantages to undergrounding besides costs. While underground lines experience fewer outages than overhead lines, it is more difficult to find faults on them than overhead lines and they take longer to repair. Underground lines are less capable of dealing with overloads and are more complicated to upgrade or modify.
Undergrounding in urban areas has several additional barriers. Underground lines need boxes for switches and other equipment. These boxes, which are located above ground, are typically six feet long, eight feet wide, and four feet high. In densely populated urban areas, there may be insufficient room in the existing utility easement for the boxes. In some cases, undergrounding existing lines would require the utility to acquire new easements. New easements may be needed when the utility only has a right to use the space above the surface or when the existing overhead route is inappropriate for an underground line, e.g., when a line goes over a water body. Obtaining new easements may be particularly difficult in urban areas where lots are small. In addition, building underground lines in an urban area may require the use of directional boring rather than trenching, which is less expensive, in order to minimize disruptions to streets and driveways.
Nonetheless, several states and many municipalities require that new distribution systems be undergrounded. The staff of the Florida commission recommended undergrounding of existing systems in several cases, such as when utilities need to relocate their lines in conjunction with road construction.
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