Slack action is still as prevalent as it was years ago.
Liquids in Tank cars slosh about and can cause wicked slack action, a bunch of loaded tanks behind a string of MT’s have been known to slosh about so much, they pop some of the MT’s of the rails; There are reports of employees who have had tanks slosh around so much that they have ripped the train apart. Autoracks, boxcars, and centrebeam/bulkhead flats with the long cushioned drawbars can cause a lot more slack action than say a grain hopper or a coal gon.
They can, loads behind empties can with slack can pop the empties off the track, or they can act like an anchor and when the crew starts pulling can stringling the empties.
- West Virginia