[cdiddy2]

It can be made on site where it is going to be used. Generally combined with a manufacturing plant

[pixl97]

Are railcars filled with pure chlorine any better? Chlorine gas leaks are deadly.

Unless you're talking about in situ chlorine production, which has its own list of issues.

[red-iron-pine]

So how do you get the precursors to the plant? You're either transporting chlorine, or you're manufacturing it in huge quantities locally, which has plenty of it's own headaches.

Either trucks or trains, and trains are more cost effective.