Why did a Norfolk Southern train derail in Ohio?

The NTSB is still investigating the cause of the derailment

Clean-up continues in East Palestine, Ohio, after a Norfolk Southern train derailed in the village, requiring the venting and burning of its cargo of flammable and hazardous vinyl chloride.

Federal and state agencies have been on scene assessing the environmental and health effects from the derailment, and political partisans have leapt on the opportunity to turn the crash into a soundbite.

The National Transportation Safety Board is in the midst of an investigation into the crash. It has released some preliminary reports, but a full report is likely still some time away.

The NTSB has already established that the immediate cause of the crash was the failure of a wheel bearing due to overheating.

"NTSB investigators have identified and examined the rail car that initiated the derailment. Surveillance video from a residence showed what appears to be a wheel bearing in the final stage of overheat failure moments before the derailment. The wheelset from the suspected railcar has been collected as evidence for metallurgical examination," the agency said in its report. "The suspected overheated wheel bearing has been collected and will be examined by engineers from the NTSB Materials Laboratory in Washington, D.C."

What is currently unknown is if there is any reason why the stretch of rail that runs through East Palestine contributed to the train's mechanical failure.

The NTSB said it plans to release further information on the nature of the derailment during a media briefing on Thursday.

At least four other trains have derailed since the Ohio train derailment on 3 February.

Cleanup gets underway at site of Ohio train derailment (Cynthia Forse Davies/LOCAL NEWS X/TMX )

In Houston, a train derailed on 13 February near Houston after it struck an 18-wheeler. The driver was killed in that accident.

A train in Detroit, also carrying hazardous materials, derailed on 16 February. No injuries were reported and none of the train's cars were breached.

Two other trains derailed as well, one in Delphos, Ohio, near Toledo, and another in Nebraska which was hauling coal.

While those numbers may seem shocking, the Federal Railroad Administration estimates that approximately 1,000 trains derail each year. The recent derailments have made headlines due to their proximity to the disastrous derailment in East Palestine.