Passport transport ran a bolt down the side of my 1968 superior hearse I had them transport back in the mid-90s. At the time it was still owned ( the company ): by the Pass family. The crease started at the front fender and ended at the quarter panel. The estimate for the repair was over $1500 at that time. They sent me a check for $300 dollars and told me they were not paying to restore my whole car. Needless to say, I never fixed the damage and I sold the coach a number of months later. A few years after the accident I talked to Robert Pass at his booth in Auburn, Indiana. I told him who I was and how unprofessional I thought his company handled things. He asked me to call him at his office the following week and we would discuss it further. I called twice and both times I left him a voice mail and my calls were never returned. I believe the company has been sold a couple of times since but I would not recommend them.
I saw a trailer burn on an off-ramp on I-35 at Story City, IA a couple of months ago. Same cause. I was actually inside of a metal building right next to the off-ramp. Now, that gets your attention when those 4 tires blow!
Step deck trailers like that use what we refer to as donut tires, 15" or 17.5" diameter to allow for the low loading height, increased interior height to be able to stack cars on the baskets in the trailer with additional clearance.
Because they turn at higher RPMs than the normal 22.5" or 24" tires on most semi trailers, keeping them inflated to spec, 120 psi is critical to prevent heat build up. It is well known operational problem in the industry, has been for years.
the routine inflation checks were likely not done, the smaller rims make it very difficult to check the inner tire for proper inflation. there are systems out there to make it easier, but they are widely ignored.
Unless it went flat very quickly, which is possible between routine walk around checks during stops, probably bad maintenance.