The bounce came from the level crossing. Rails naturally move on ballast to accommodate the weight. At a crossing the street is a firm base which does not allow the rails to go down. Therefore the train actually rises across the level crossing and resettles to its original traveling height. If you watch to end you'll see the bounce almost completely disappears.
I drove for a guy who lived to pace trains and yours is a beautiful steady work. Made me go back to an old favorite. One 30 years ago with 3 MILW RD GP40s on an empty grain train in North Dakota esp watching those couplers bounce
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