“Most derailments are relatively benign, and can be compared to a person walking down the street, tripping, getting back up, and continuing on her or his way,” University of North Dakota mechanical engineering professor George Bibel wrote in “Train Wreck: The Forensics of Rail Disasters” in 2012. “… Yet derailments have been responsible for some of the greatest train wrecks ever.”

In Philadelphia late Tuesday, it seemed Amtrak was facing one of its most serious wrecks in recent years. As a swarm of flashlights and floodlights swept the scene of an Amtrak derailment in Philadelphia late Tuesday, the spectacle was horrific. A train car rolled on to its side. Emergency responders uncovering bodies. A survivor covered in grime sipping from a bottle of water in a daze. The toll, as of Wednesday morning: six dead, more than 140 hospitalized.

Amtrak derailments have been flat in recent years, according to the Federal Railroad Administration’s office of safety analysis. But the first two months of 2015 have seen more derailments than comparable periods in previous years.

An Amtrak train derailed in North Carolina in March. An Amtrak train derailed in Massachusetts last June. An Amtrak train derailed in South Carolina the year before that.

Amtrak derailments have increased in recent years, according to the Federal Railroad Administration’s office of safety analysis. There were two in 2012, three in 2013, six in 2014, and there have been nine this year.

Why do Amtrak trains derail with such frequency? Although the cause of Tuesday’s derailment was still undetermined, the answer has a lot to do with the United States’ crumbling transportation infrastructure, and a little to do with freak accidents. The United States’ lack of interest in funding rail transportation has been long-lamented. Amtrak, a federally subsidized for-profit corporation that doesn’t turn a profit, is a Republican punching bag — the subject of a perennial struggle for funding on Capitol Hill.

“While Amtrak isn’t currently in danger of being killed, it also isn’t likely to do more than barely survive,” Simon Van Zuylen-Wood wrote in the National Journal last month. “Last month, the House of Representatives agreed to fund Amtrak for the next four years at a rate of $1.4 billion per year. Meanwhile, the Chinese government — fair comparison or not — will be spending $128 billion this year on rail.”

The result: a system that connects the nation and posted record ridership in 2013 but can’t always pull its freight.

“The problem that you have — and you’ve had it since 1976 and even before — is that there’s never been an investment program that would bring the infrastructure up where it belongs on existing capacity,” Amtrak chief executive Joseph Boardman told the Atlantic last year. “There isn’t even an understanding about the need to increase capacity in order to continue to increase the GDP in this nation. Not only on the Northeast Corridor but all over the country.”

Amtrak was faced with mechanical problems almost immediately after opening for business in May 1971. A month later, it was counting bodies.

“Amtrak train No. 1, a southbound passenger train operating on the tracks of the Illinois Central Railroad between Chicago, Illinois, and New Orleans, Louisiana, derailed near Salem, Illinois, on June 10, 1971,” the National Transportation Safety Board reported. “Two locomotive units and the first seven cars were turned over on their sides. The derailment resulted in 11 fatalities and 163 injuries.”

A mechanical failure in a wheel caused what was called “the first major accident under the Amtrak system.” Tighter safety regulations were recommended,  and although all train derailments — not just Amtrak’s — have fallen since 1980, most continue to be caused by such problems.

“Derailments are usually caused by equipment failures,” Bibel wrote. “Broken, settled, spread, shifted, or overturned rails account for about 50 percent of the equipment related derailments.”

However, human and environmental factors can also contribute to train accidents.

“Poor train handling, incorrectly set track switches, unsecured cars on a hill, shifted loads, vandalism, or obstructions on the track are among the human causes of derailments,” Bibel wrote. “Derailments can also be caused by flash floods, avalanches, rock slides, and high winds.”

Perhaps the worst Amtrak derailment that resulted from human error came on Sept. 23, 1993. More than 40 people died in Alabama when a train “hurtled off a 12-foot-high trestle into a bayou and caught fire, trapping sleeping passengers in black water up to 30 feet deep,” as the New York Times put it. What’s known as Big Bayou Canot train wreck is still the deadliest crash in Amtrak’s history.

“We were throwing sheets and blankets out of the cars that were still on the track to the people who were wet from being in the water,” a survivor told the paper. “Some people were hysterical. There were a lot of old people on the train.”

The crash occurred less than 10 minutes after a river barge hit the trestle, displacing the track. Among other causes, the NTSB blamed reduced visibility and “the pilot’s lack of radar navigation competency.”

Amtrak can’t be held responsible for acts of God, rail-jumpers or people who park houses on train tracks. But it will have to find a way out of its endless fiscal crisis if it is to survive and thrive.

“There was no question that it would probably not pay for itself,” Anthony Haswell, who lobbied for the creation of Amtrak, told the National Journal. “But the Nixon administration and other conservatives thought that once it was demonstrated that it wouldn’t pay for itself, it would be abolished.”

Correction: An earlier version of this story inaccurately reported the rate of recent Amtrak derailments. The story has been corrected.

Aerial visuals revealed the extent of wreckage after an Amtrak train derailed in Philadelphia killing at least six people. (Reuters)