Container Tugs and Container Frames
For freight that is not time critical or immune to the conditions of space (ore minerals, building materials etc.) Container tug trains are a cheaper alternative to Freighters. Most Container tugs are unmanned robot tugs and run back and forth the same routes.
Large Tug Trains of 200 km and more meters length are not uncommon, although the average Tug train is about 20 kilometers long.
Container Frame Ships are often used in express freight roles or for perishable items.