4 facts everyone should know about train accidents

The derailment of an Amtrak train Tuesday night in Philadelphia has killed at least six people and injured dozens more.

We still don't know the cause of the accident. But we do know some basic facts about train safety that can help put it in context.

1) Train travel is much safer than other forms of travel

Train accidents are terrifying, and get lots of public attention when they occur. But the truth is that — just like plane travel — on a per-mile basis, riding on a train is much safer than in a car.

The most recent comparison study, conducted in 2013 by economist Ian Savage, compared fatality rates for several different forms of travel in the US.

The number of rail deaths from year to year ranges widely (because many can happen in large, sporadic accidents), but between 2000 and 2009, a person was about 17 times more likely to die while traveling in a car, compared to a train, for the same distance:

(Javier Zarracina/Vox)

2) Derailments are fairly common — but most are relatively harmless

Across the US, trains derail more often than you might think — last year, for instance, there were a total of 1,241 derailments. But the majority of them cause no injuries or deaths, and often only cause damage to the cargo they're carrying.

This is partly because just a slim minority of US trains carry passengers (most carry freight), and because most trains cars are designed to survive some level of impact. Additionally, most miles of track are in relatively rural, unpopulated places.

The Washington Post highlights a good analogy on this, which comes from George Bibel's book Train Wreck: The Forensics of Rail Disasters:

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. Unless derailed cars crash into houses, strike passenger trains, or release hazardous material into a neighborhood, derailments do not normally affect civilians.

3) Derailments have been getting less common over time

Bibel also notes that derailments have become dramatically less common over the years, with a huge dip in the annual rate in the 1980s:

(George Bibel)

There's been a similar dip in fatalities per passenger mile, Savage has found.

The decline was mainly caused by improvements in technology that were implemented after the freight industry was heavily deregulated in 1980, allowing companies to turn a profit, so they could invest more in track and new equipment.

Years ago, for instance, engineers were required to manually spot track signals and stop their trains to prevent collisions. Nowadays, automated systems do that, as well as monitor train speeds to ensure they don't exceed preset limits.

4) Derailments are most often caused by track problems

(Javier Zarracina/Vox)

Derailments can sometimes be caused by operator error or equipment malfunction — but more often, they're due to track problems. As Bibel notes in his book, "Broken, settled, spread, shifted, or overturned rails account for about 50% of the equipment related derailments."

We still don't know the cause of the Philadelphia derailment, but it's worth noting here that some of the decline in overall train derailments has been driven by huge investments freight companies have made into maintaining their tracks. As the Omaha World-Herald noted last year, the freight company BNSF spent $5 billion on it in 2014.

The same can't be said for Amtrak. The system has been underfunded for years, and federal legislation requires it to use the revenue it generates in the busy Northeast Corridor (where most of its riders are) to subsidize operations on the rest of its network, which lose money.

This has led to deteriorating track conditions in the Northeast (Amtrak trains ride on tracks owned by freight companies elsewhere), even as passenger numbers steadily climb. It's impossible to say for sure, but this may have played a role in Tuesday's derailment.

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