Repost from The Missoulian
[Editor: Significant quote: “the cars were rigged with double shelf couplers designed to prevent individual cars from detaching and potentially causing punctures.  ‘This safety feature of the tank cars worked properly, resulting in all 30 cars rolling on their side(s), as designed,’ Lewis said in a written statement.”
Here is more about double shelf couplers.  And note p. 23 of a 2010 Transport Canada study which found that “Double shelf couplers also have disadvantages: sometimes string of ’empty’ tank cars derail.”  – RS]

Montana Rail Link: Trains collide, tank cars derail in Missoula

An early Tuesday morning train collision in the Missoula rail yard resulted in the derailment of 30 empty tank cars but no injuries or spills.

Montana Rail Link officials said the accident occurred about 4 a.m. when a rail car loaded with company scrap metal made low-speed contact with a stationary empty tank car coupled to 29 others.

MRL spokesman Jim Lewis said the cars were rigged with double shelf couplers designed to prevent individual cars from detaching and potentially causing punctures.

“This safety feature of the tank cars worked properly, resulting in all 30 cars rolling on their side(s), as designed,” Lewis said in a written statement.

Lewis said there was minimal equipment damage. The loaded car did not derail and was moved from the site.

Crews with heavy equipment started putting the tank cars back on track before noon and worked until 8 p.m. They’ll resume Wednesday morning, Lewis said.

Mainline service was not interrupted, and the cause of the incident is under investigation.

MRL has released no further word on its investigation into a collision east of Missoula near the mouth of the Blackfoot River on Nov. 13. That crash resulted in the derailment of three locomotives and 10 empty grain cars.

Both engineers in one locomotive were hospitalized and released. The shells of the grain cars remain along the tracks by a trestle below the former Milltown Dam as salvage work continues.