Every Thursday, the Association of American Railroads reports weekly rail traffic in the U.S. They specify how much of the rail traffic was carloads and how much was intermodal.
The U.S. Department of Transportation explains:
Carload traffic is comprised mostly of bulk commodities, such as coal (46% of rail tonnage in 2001), agricultural products, and nonmetallic minerals and products, while rail intermodal transports a huge range of goods from bicycles to automotive parts, lawnmowers to glassware, greeting cards to bottled water, and toys to computers. Through globalization manufacturers supply chains have become widely distributed geographically, and rail intermodal plays a critical role in making supply chains more efficient for retailers and other firms and industries.
From the best source on the web, intermodal containers are:
A standardized reusable steel box used for the safe, efficient and secure storage and movement of materials and products within a global containerized intermodal freight transport system. “Intermodal” indicates that the container can be moved from one mode of transport to another (from ship, to rail, to truck) without unloading and reloading the contents of the container. Lengths of containers, which each have a unique ISO 6346 reporting mark, vary from 8 to 56 feet (2.438 to
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