Pretty much only the largest systems need enough to use rail - a little Chlorine goes a long way in water! But having handled it both ways, from a safety standpoint I would rather see Chlorine in a rail tankcar than an over the road truck any day and twice on Sunday!
But there is another important factor that also drove system operators away from Chlorine which was if you have a little bit of low molecular wt organic material in your feed supply, Chlorination will help you generate halogenated organics - which is to say potential carcinogens. For instance Ann Arbor, which takes some water from the Huron river - which being a live ecosystem of course does carry some organic material, switched for that reason.
Given the dilution volume of the Great Lakes, the Detroit system, which draws mostly from Lake Huron, has organic concentrations low enough that is apparently not an issue.