Replacing old or damaged gas pipelines was found to have significant, beneficial impacts on cities. A recent Stanford University study found that city pipeline replacement programs could reduce natural gas leaks by 90 percent.

"The surprise wasn't that replacement programs worked," Rob Jackson, the Michelle and Kevin Douglas Provostial Professor at Stanford, said in a news release. "It was that they worked so well."

Invisible gas leaks from pipelines contribute to global warming and, in extreme cases, can even cause explosions. The researchers measured gas leaks in cities using cars equipped with methane-mapping instruments. They drove through Manhattan, NY, Cincinnati, OH, and Durham, NC. When comparing all the cities, they found that in Cincinnati and Durham there were less leaks per mile. This is because outdated pipelines have been replaced by public-private partnerships in these areas, as the release noted.

"Infrastructure investments save lives, help the environment, and, over time, will put money in people's pockets," Jackson explained in the release.

While natural gas pipeline safety in the U.S. has improved, there is still more that needs to be done. In 2014, there were 18 deaths and 93 injuries from pipeline-related incidents. That same year, old pipelines also resulted in $2 billion worth of lost natural gas. Leaking gas and methane also affect the environment, because methane is a powerful greenhouse gas, and because hydrocarbons cause ozone to form.

"The oldest cast iron pipes were laid in the 1800s. They're well over a century old," Jackson said in the release.

According to the news release, Durham replaced all of its cast-iron and unprotected-steel pipes, and similar projects in Cincinnati are almost complete. However, in Manhattan, there are still hundreds of miles of old and damaged pipes underground.

"It's not just U.S. cities," Jackson said. "There are many cities in Europe and elsewhere with old, unprotected piping. We need smart financial incentives to upgrade our oldest pipelines. It's time to get them out of the ground."

Their study was recently published in the journal Environmental Science & Technology Letters.

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