From wikipedia
> United States – BNSF Railway and Union Pacific Railroad (UP) regularly operate intermodal container trains exceeding 5,000 metres (16,500 ft) in length on main lines in the western United States. On the UP, these trains can stretch to over 6,100 metres (20,000 ft) with 5 locomotives and 280 well cars.
Those are incredible figures. It would almost be a shame to ban such amazing monuments to engineering. Not to mention that it's probably the most efficent and enviromentally friendly way to do things.