oil-train-railBakken Shale crude oil shipments via train have resumed in North Dakota, but there remain unanswered questions about what caused 10 tanker cars to derail and ignite in Heimdal, ND, earlier this month.

A spokesperson for BNSF, the railroad involved in the derailment, told NGI‘s Shale Daily on Tuesday that the National Transportation Safety Board (NTSB) continues to investigate the May 6 accident, and the company is prevented from disclosing “any information that is germane” to the investigation.

In Washington, DC, an NTSB spokesperson said a final report, including identifying the cause of the incident, is likely to take up to a year, but some interim reports may be issued. NTSB’s Jim Southworth has been the investigator-in-charge.

Read more from NGI’s Shale Daily.