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A train carrying crude oil derailed and exploded Monday in central West Virginia, sending oil into the Kanawha River and forcing the shutdown of the Fayette County's main water intake plant while officials continued to test for releases.

It's the first serious incident involving oil rail tankers in the U.S. of 2015, but it is unlikely to be the last. The number of accidents has been increasing in recent years as the amount of oil transported in the U.S. has exploded.

Meanwhile, Congress passed a bill last week authorizing construction of the Keystone XL Pipeline. President Obama is expected to veto it, but even when that happens, the project still won't be dead, as Congress could find votes to override the president's veto. And in any case, the North American shale oil boom shows no signs of slowing.

So which of the two modes of transporting oil is safer: rail or pipeline?

In 2013, a Canadian think tank published a report arguing pipelines were safer than rail. The 10-year average for the frequency of liquid leaks was approximately three leaks per 1,000 km of pipeline, the Fraser Institute found—a “remarkably small” average considering that Canada produces and transports 3.2 million barrels of oil each day.

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But some found the Fraser report flawed. In an op-ed for The Huffington Post, Peter Goelz, the former managing director of the National Transportation Safety Board, accused the report's authors of cherry-picking data.

When it comes to environmental impact, he said, railcar accidents actually tend to be limited: The overwhelming majority of rail spills reported to the Department of Transportation are usually less than five gallons.

As for pipelines, Goelz writes, "when [they] have a problem it is almost always a big one."

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The best example of this occurred in North Dakota in 2013, he said. A pipeline owned by San Antonio-based Tesoro spilled nearly 20,600 barrels of oil in what Goelz says was the largest inland pipeline spill in recent U.S. history.

And it took two weeks for authorities to notify the public of the spill.

"Even the pipeline company cannot explain how long the leak was active, let alone what caused it," Goelz wrote.

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In the U.S., the incidence of serious oil and petroleum product pipeline disruptions (ones involving injury or death) has been mostly unchanged despite the oil production boom of the past few years.

The International Energy Agency recently analyzed U.S. incident data and largely came to the same conclusion as Goelz. Rail incidents outnumber those of pipelines two to one.

But, "the average pipeline spill was far graver," analyst Charles Esser wrote last May.

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In January, a ruptured pipeline dumped approximately 40,000 gallons of oil into the Yellowstone River in Montana, the second time an incident had occurred there in four years. Last week, Montana Governor Steve Bullock called on the Obama administration to beef up federal subterranean pipeline rules that right now require them to be buried just four feet beneath the ground

Rail accidents often seem worse, but usually lead to less damage for everyone involved than pipeline mishaps.

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Exxon's two Yellowstone incidents, as well as its 2013 Pegasus disaster that cleared out the town of Mayflower, Ark., will result in millions in fines and lawsuits.

Whereas this Lynchburg, Va. accident, which looked terrible…

…Resulted in very little damage. Virginia's governor merely convened a roundtable to discuss rail safety.

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The property damage from pipeline incidents soars into the hundreds of millions each year.

Whereas Politico recently reported that damage from rail spills just reached $10 million in 2014.

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Still, risks from rails are going to be around for awhile. While less than 10 percent of U.S. crude gets taken by train, most of the oil coming out of North Dakota's booming Bakken play does so, and the government now says the specific oil found in the Bakken is especially flammable.

Regulators are now seeking to impose a rule that would require oil rail cars to be redesigned to further reduce spills on derailment. But the largest car manufacturer can only change out 8,000 cars a year, leading one U.S. Congressman to fear that replacing all affected cars could take a decade.

And the Wall Street Journal recently reported that not everyone knows the extent of rail oil routes.

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ProPublica's Lena Groeger compares pipeline incidents to airplane fatalities: rare, but disastrous when they do happen. And pipelines lack the same degree of federal oversight that airplanes have: just 44 percent of all hazardous liquid lines are subject to rigorous inspection criteria and inspected regularly, she says. All other links are inspected irregularly.

Goelz writes that both pipelines and railroads deliver more than 99.5% of their crude oil product safely.

Most environmentalists say the debate over whether pipelines are more dangerous than rail largely misses the point.

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“The best data I’ve seen indicates, depending on your perspective, both are pretty much as safe as each other, or both are equally unsafe," Edward Whittingham, the executive director of the Pembina Institute, an environmental group based in Calgary, Alberta, told the New York Times last year.

"There’s safety and environmental risks inherent in either approach.”

Rob covers business, economics and the environment for Fusion. He previously worked at Business Insider. He grew up in Chicago.