Track movement under freight train

[RobertInOntario]

I was watching a CNR freight train thunder through at a grade crossing today and I couldn't help but notice how much the track was moving up and down under the weight of the freight cars! I've actually seen this before in one of my other favourite train-watching locations.

It wasn't a whole lot different from how my track on my HO layout moves up and down (under the weight of my model trains) when it's not properly glued down or ballasted! This got me thinking, how common is this and how safe is this extra movement or play?

In June, I spent a day helping at one of the heritage railways that I visit. Staff there said they're out doing track maintenance work every week, and have to adjust/fix the ballast, gauge and positioning of the rails, etc. I suspect that this location (near the grade crossing) might need some maintenance?

Thanks,
Rob