It could have been worse. The crew of the CSX freight train that derailed last month in Virginia escaped injury, but the incident caused millions of dollars in damages to the train, the track and a bridge.

A possible culprit: the 5 ½ inches of rain fell in the area during the ten days before the accident, and that subgrade fill was subsided from the track structure near a curve.

Connecting these dots has not yet been done; a National Transportation Safety Board (NTSB) investigation into the May 19 incident near Alexandria is ongoing, with a specific cause yet to be determined.

What is known is that the 9,910 foot long train, which consisted of 3 locomotives and 167 freight cars, was not transporting hazardous materials. The train was traveling at about 38 mph at the time of the derailment. Damage is estimated to be between $5 and $7 million.

From the preliminary report:

An investigation revealed an area in a curve where the subgrade fill was subsided from the track structure. The investigators found that this fill was subsided for about 26 feet (at a depth of 18 inches) at MP 102.9.

There was a flange mark traversing over the top of the rail head in the curve and at the location of the subsided subgrade.

How NTSB is getting info

In addition to on-scene inspections of the track structure, the signal system, and the mechanical equipment, investigators are getting data from an event recorder and video from the forward-facing video recorder downloaded from the lead locomotive. They are also collecting and examining maintenance records and interviewing the CSX train crew and other CSX personnel. Additionally, An NTSB aerial drone recorded the accident scene, especially the derailed equipment and the damaged bridge. (View from a drone shown above.)

The NTSB formed the following technical investigative working groups:

• Signal Systems
• Track and Engineering
• Mechanical/Equipment

Parties to the investigation include the Federal Railroad Administration, the Virginia State Corporation Commission, CSX, and the Brotherhood of Maintenance of Way Employees Division.