This likely was caused by foundation being too soft, wet road beds can't handle the impulse loads that locomotives present upon them. Tacoma is Seattle weather wise and you are wet most of the time.

And they went too fast. You have all manner of speed traps on this in USA.

I can talk about Norfolk Southern over the gorge in Letchworth Park south of Buffalo NY. Or a water tower in Maricopa AZ where freights roll past at 70mph+.

You have lots of problems and bridges are part of that.

PLUS Amtrak rides on freight rails. They should be using their own.