In a previous job (one where I was paid very little, lived in the desert, and wore a uniform to work) I worked within spitting distance of the concrete pad where they loaded and unloaded the OST trailers. I won't go into detail, but the safety measures that prevent unauthorized persons from accessing the trailer contents are serious enough that I wouldn't wish to ever be on the authorized crew that loads and unloads them.
Also, you can sometimes tell that the plain jane tractor trailer is a SST (Safe, Secure Transport) because it's surrounded by a convoy of Suburbans with a wide variety of antennae, and a full load of US Marshals armed to the teeth. They don't go anywhere without that.
They can flip 'em over in ice storms all day for all I care. Any group who wants to can try to steal the cargo for all I care. I have zero worries about the contents of these vehicles. They are safer than just about anything else in the world.