A new study found that cities that regularly replace old natural gas lines don't leak as much methane as older cities who don't fix them.

Using a gas-sniffing device attached to Google's city-mapping cars and new calculations that determine rough leak rates, the Environmental Defense Fund measured in the streets of the three cities, Indianapolis, Boston and New York City's Staten Island. Methane is a potent global warming gas and leaks can be a safety hazard.

While Boston and Staten Island averaged one leak per each mile mapped, Indianapolis, where the public utility has replaced old pipes, had 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.