If people realized what was moving by rail or truck through their neighborhoods they'd freak. Do you realize the US Govt moves nukes by unmarked semi all the time? The security is primarily the trucks anonymity. About 20 years ago one of them hit a patch of black ice in NW Nebraska and ended up in the ditch. Sheriff came to assist and found the driver brandishing a M-16 and ordering them to stay away. Once they verified the drivers story and who he worked for, the Sheriff was astonished to learn that his county was a regular transit route for nuclear weapons.
There a quite a few other non-nuclear items I'm aware of that ship by rail in plain freight cars or trailers and again, the shipper depends on the load not sticking out and your not giving it a second thought even thought you might be 10 feet away when it passes you at a road crossing.
Guns are way down the list of things to worry about