Hurricane Sandy cuts power for millions. Why aren't utility lines underground?

Hurricane Sandy caused a record storm-related power outage in New York City and has more than 7.4 million homes and businesses without power. So why aren't cities burying more power lines underground to avoid the blackouts?

Hurricane Sandy left more than 7.4 million homes and businesses without power and knocked out mass transit along a wide swath of the eastern United States from the Carolinas to the Canadian border.

It will not be the first time – nor will it be the last time – a major storm knocks out power for millions. High winds, broken tree limbs, and lightning strikes are a familiar foe to exposed, elevated cables.

The question arises: Why aren't power lines underground? 

Some already are. San Diego has been putting utility cables underground since 1970 and hopes to bury all residential-area lines within the next half century. In 2003, the California Public Utilities Commission approved an "undergrounding" surcharge on San Diego residents' electricity bills. The city buries 20-25 miles of utility lines each year at an annual price tag of $54 million, according to its Utilities Undergrounding Program website.

After last October's surprise snowstorm left 3 million in the dark across the Northeast, Boston Gov. Deval Patrick entertained the idea of buried power lines during a press conference.

“I love the idea," the governor said. "Apparently, though, that is a $1 trillion project across the commonwealth. And that cost and how to pay for it, no one has answered yet."

Therein lies the challenge. While it may seem logical to bury utility cables to avoid the inconveniences and dangers of downed power cables, the upfront costs of transplanting is steep.

Building new underground transmission lines is five to 10 times more expensive than putting up overhead transmission lines, according to 2009 study by the Electric Edison Institute, an association of shareholder-owned electric companies. So the costs of converting from an overhead to an underground system range anywhere from $80,000 per mile in a rural area to $2.1 million per mile in a city. 

Even when the cables go underground, they aren't necessarily 100 percent protected from nature's wrath.

In Manhattan, there are about 21,000 miles of underground cables. Nevertheless, most of downtown Manhattan was darkened Monday by power outages because of hurricane Sandy's record storm surge of nearly 14 feet, which caused widespread flooding. Consolidated Edison, the utility serving the area, had warned on Sunday that it could cut power to customers in Lower Manhattan to help protect the cables from flooding.

In all, more than 650,000 customers in New York City and Westchester County lost electrical power due to the hurricane, three times the number affected by hurricane Irene in 2011, the utility said.

"This is the largest storm-related outage in our history," John Miksad, Con Edison's senior vice president for electric operations, said in a statement Tuesday.

Even if the frequency of outages is diminished with underground cables, some studies show that the duration is not. A comparison by North Carolina’s investor-owned electric utilities found that the average duration of an underground outage was 58 percent longer than an outage in overhead cables.

Despite the drawbacks, many still call for subterranean utility cables. Underground cables are less vulnerable to natural disasters and pose a lesser threat to wildlife and low-flying aircraft, advocates say.

It's an easier case to make when overhead cables sway in gale force winds. 

– Material from the Associated Press was used in this report.