Investigators found that the accident was caused by a defect in the track. The defect had been spotted — one day before the derailment. And it had been scheduled for maintenance — one day after the derailment. It was the 48 hours in between that posed the problem. More frequent inspections might have identified the safety issue sooner, before it declined into a catastrophic failure.

The NAS also questioned new regulations established for oil train speed limits. Speed limits are now 50 mph in most areas and 40 mph in urban areas. But some safety experts say that speeds should be reduced to 30 mph for safety.

The oil industry says that the new regulations, speed limits included, are working. Last year saw the fewest oil train derailments on record.

The industry also says that lowering speed limits further would increase congestion, as trains could not clear the tracks as quickly. That’s a legitimate concern, even for passenger train travelers: Passenger and freight trains must share the same tracks, and longer, slower freight trains already are causing delays in Amtrak schedules, here and across the country.

The scientists also say that emergency responders should be better trained to deal with derailments when they do occur, a recommendation that also has been put forward by others.