Answer: Air transport offers the primary advantage of speed over long distances, but it imposes limitations on the size, shape, and weight of shipments. It also tends to be the most expensive form of transportation; however, when speed is a priority, air is usually the only way to go. The cheapest method of transportation is via water, and this is the preferred method for such low-cost bulk items as oil, coal, ore, cotton, and lumber. Water transport is slow, however, and like rail, must be combined with another mode of delivery for most shipments. Intermodal transportation refers to the coordinated use of multiple modes of transportation, particularly with containers that can be shipped by truck, rail, and sea. Shippers can combine the benefits of multiple modes by using intermodal transportation. With containerized shipping, for instance, standard-size freight containers can be moved from trucks to railroads to ships for maximum flexibility.