Technically, tritium is a hydrogen atom with two neutrons (atomic weight of 3, hence the "tri" in tritium.
But it doesn't exist in nature - hydrogen itself (without the extra neutrons) is pretty rare in nature - it's too reactive chemically.
So normally they're talking about "heavy water" - water with a higher than normal concentration of tritium atoms making up the H2 part of the H2O.
Yes, it's slightly radioactive, and yes it is what makes watch hands and night sights glow in the dark. But it's not dangerous, just very, very expensive (but a little goes a long way).
I've transported it in small vials (in a box) when I worked for a courier years ago - nothing special there. I can't imagine why a tanker would haul it unless we're talking a huge quantity, and the only people that need huge quantities of heavy water are people making it (ie, nuclear power plants) or people building boosted fission bombs (read Clancy's "The Sum of All Fears for an explanation of that one, but don't try it at home).
