In liquid form absolutely agree.
But hexane is quite volatile so you can get a vapour mix fairly easily.
I have done this demo using methylated spirits by shaking the can before lighting and you get a nice boom.
Getting a whole truckload to be stable for most of the journey and then to mix enough to go boom on the bridge is not in within the expertise of this chemistry teacher but I can see it might be possible.
Interesting point about Hexogen, but would be harder to hide it.
@CanadaPlus
It is a really cool demonstration though - and very useful for showing quite a few different things by changing the fuel.