Everything you need to know about Amtrak

Emergency workers continued combing through the wreckage early into Wednesday morning after an Amtrak train ride carrying hundreds of passengers turned deadly the previous night, derailing just north of Philadelphia and killing at least six people.

Related: The latest on the Amtrak train derailment

Federal investigators are still searching for details explaining what caused the crash, which occurred on the busiest stretch of railway in the Northeast. Here's everything you need to know about the backstory to the Amtrak derailment:

Train fatalities number in the hundreds annually: According to the Federal Railroad Administration, trains killed 813 people in 2014 alone, including 226 deaths on Amtrak and other commuter railroads. The agency says the vast majority of fatalities are avoidable -- highway-rail crossing and trespassing fatalities account for nearly 96% of all rail-related deaths. 

The track location has a deadly history: One of the worst train derailments in American history occurred on the same stretch of track 72 years ago when a 16-car Pennsylvania Railroad Congressional Limited train carrying military servicemen to New York on Labor Day careened off the track. The deadly crash killed 79 people and injured another 117. Investigators later concluded that the journal box had burned off and an axle snapped at high speeds.

Chinese rails receive billions more in revenue: Critics have called for more funding for the federal government in order to replace aging and archaic infrastructure. But according to the National Journal, the House of Representatives has called for $1.4 billion annually for Amtrak. Compare that to the $128 billion the Chinese government will be funding its rail system this year. 

Thousands of trains operate same route: More than 2,200 trains take the Amtrak Northeast Corridor each day, making the route connecting Washington, Philadelphia, New York and Boston the busiest stretch of railroad in North America.

The 456-mile northeast corridor services more than four-times the number of passengers than the second busiest railway, carrying more than 11.4 million passengers a year.

Northeast Amtrak out-paces major airline travel: Amtrak recently saw its largest number of total passengers in its history, with 31.6 million passengers who used the rail service in 2013. On average, more than 86,000 passengers ride more than 300 Amtrak train daily.

For some perspective, more than three times as many people took Amtrak between Washington, D.C., and New York City as the airline industry.