A Mississippi barge is about 1,500 tons capacity, a truck is about 25/26 tons, and each rail car is about 100 tons. Barges are grouped in 15 barge tows, and trains are grouped in 90 to 125 car unit trains.

Its a bit easier to get the trains than that many trucks. Also considering that can do barges can almost always do trains. Its not ideal and barge would be preferred, obviously.