Apparently there was no bomb; the driver fell asleep and hit a sign standard, which ruptured a fuel tank and set the dual trailers on fire.
I have to say I was a bit dubious when I considered that there was no crater and the tractor was practically unscathed. But I can see why it was treated more seriously than otherwise might have been warranted by the responding officers.
My next question is how in hell a truck driver running one of those tandem rigs falls asleep at the wheel. An inspection of his log will probably show that he wasn’t taking his mandated breaks and was way over on his driving hours.
And they not only want to keep driving the tandem rigs, they want to drive triples, too. Didn’t these people ever hear of the railroad?
A "surly curmudgeon[], suspicious and lacking in altruism." (Robert A. Heinlein)