Those trailers are really low. Guaranteed he got high centered and as soon as that happens all the weight comes off the drive tires because the air suspension dumps. The tires now have just slightly more traction than if they were hanging in mid air.

Been there, done that. Fortunately not on a raised crossing but still needed a wrecker to get pulled off. Actually 2 of them and it didn't come back a foot and I was free.

Kevin