WASHINGTON (AP) — Cities such as Indianapolis that regularly replace old natural gas lines have significantly fewer leaks than older urban areas where they don't, like Boston and New York City's Staten Island, according to a new study by Google and an environmental group.

Using a gas-sniffing device attached to Google's city-mapping cars and new statistical calculations that determine rough leak rates, the Environmental Defense Fund measured the key component, methane, in the streets of the three cities.

Boston and Staten Island averaged one leak per each mile mapped. In Indianapolis, where the public utility has replaced old pipes, there was only one for every 200 miles mapped. And Boston and Staten Island leaks were more likely to be bigger, more than 2,000 cubic feet per day of the potent global warming gas.

Methane traps 84 times more heat than carbon dioxide, but after a couple decades, methane disappears and carbon dioxide sticks around much longer. Reducing methane is an important tool in fighting climate change because it is so short-lived but powerful, said the advocacy group's chief scientist Steve Hamburg. Companies want to reduce leaks because it saves them money and the environmental group hopes to map more cities and develop a better tool to reduce leaks.

These are usually not the type of leaks that are considered immediate safety hazards in terms of explosions and are more nuisance types that are repaired on a regular but not urgent schedule, said Sue Fleck, a vice president of National Grid, a Boston natural gas pipeline firm.

Explosions from ruptured or leaky gas lines killed eight people in New York City's Harlem earlier this year and eight people in San Bruno, California, in 2010. These leaks are not likely the type behind those tragedies, Fleck said.

The study is not peer-reviewed. Previous studies published in scientific journals showed large leak rates in Boston and Washington, D.C. and outside scientists who study methane leaks said there wasn't too much new in the latest study except for the addition of leak rates and they questioned how they were calculated.

Still, Rob Jackson, a Stanford University professor who studied Boston and Washington, said he was surprised by how few leaks the Google study found in Indianapolis. A previous study shows that Boston, parts of New York, Washington, Philadelphia and Baltimore are among the slowest to replace old pipes, while Cincinnati, Birmingham, Alabama, and Chicago are among the fastest.

The new study "shows us that policies to replace old pipes matter," Jackson said. "It doesn't have to be like Boston or D.C."

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Online:

Environmental Defense Fund study: http://www.edf.org/climate/methanemaps