"Today, the rail administration says it lacks enough evidence that long trains pose a particular risk."
This is ridiculous, in fact outrageous. We've been using trains and railroad technology for about two hundred years and the engineering is well understood. If procedures now require trains to exceed the once-understood safe limit of 1.4 miles then administrators should automatically set up a testing program to determine new parameters and operational safety limits.
What's the purpose of having regulators who cannot act proactively before an accident? If operational parameters change from the accepted norm or standard then then a reappraisal of the regulations should happen automatically.