Axle is an easier way of dumbing that down for people. My point remains. The rules which Ben posted still do not pertain to wheel bearings. Wheel bearings do fail at random times even with maintenance. We struggle with this in the rail industry and truck industry. It’s why you also see so many truck fires. It’s a cheap component prone to failure. I have seen ones with less than 5000 mi on them blow apart in wheels. It’s literally nothing new. Additionally I have not seen any reports yet that this train threw any hot boxes along the line so it likely happened at a rapid pace.