A massive derailment of an Amtrak train in Philadelphia claimed the lives of at least six people and injured another 140 people on Tuesday night, just one of a handful of fatal train accidents this year. Derailments are by and large the leading cause of train crashes in the United States. Between 2001 and 2010, of the 58,299 train accidents that occurred, 54,889 were train derailments. That’s a staggering 94 percent.

Officials have not yet determined the cause of last night’s Amtrak crash, but historically, broken rails and welds are the most common cause of train derailments. They account for more than 15 percent of derailments, according to data from the Federal Railroad Administration.

Broken rails and welds were more than twice as likely to have been the cause of train derailments than the second and third leading causes—track geometry and bearing failure. Track geometry, which includes such things as train alignment, gauge and elevation, was responsible for 7.3 percent of derailments and bearing failure was responsible for 5.9 percent.

Carrying 238 passengers and five crew members, the Northeast Regional Train 188 was bound for New York City when it crashed at 9:30pm in the Port Richmond region of the Pennsylvania city. Six of the train’s seven cars overturned in the accident, and while the majority of passengers were able to walk away from the accident, 65 people were taken to nearby hospitals.

Between 2005 and 2014, Amtrak had the second highest number of reported accidents and incidents, outstripped only by the Union Pacific Railroad company. Over the period, 20,703 accidents involved Union Pacific trains compared to the 18,460 that involved Amtrak trains. The two railroads accounted for 16.3 percent and 14.6 percent of all train accidents between 2005 and 2014.

It is important to note, however, that both of these railroads run trains much more frequently, so while the number of accidents is higher than others, that is not necessarily reflective of the general safety of the railroads.

This article is reproduced with permission from Vocativ (© Vocativ). The article was first published on May 13, 2015.