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A westbound Union Pacific Railroad double-stack container train crosses the Keddie Wye trestle in the Feather River Canyon of northern California. The train's containers are bound for the port of Oakland. (Photo by Ernest H. Robl; transparency file no. 960154)
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For information on photos used in this document, please contact ehr@mindspring.com. Or, call (919) 401-9480.
This document consist of the following sections:
Because the subject of intermodal containers continued to come up in both prototype and model discussions on the net from time to time, and these discussions frequently brought out conjecture and incorrect assumptions about containers, I first put together this FAQ on the subject of containers in 1995.
The initial document was distributed through several internet news groups. In 1996, the document was converted to an HTML Web page and enhanced with photographs. The document has grown considerably since its initial version, in large part due to comments and suggestions received from many people in the transportation and logistics business. This feedback is hereby gratefully acknowledged.
As a writer/photographer specializing in transportation subjects, I've visited a number of container facilities in both the U.S. and Europe. I also keep up with a variety of transportation trade publications which cover developments in this area. So, the following information is based on personal observation as well as reference works.
The following discussion is restricted to containers designed to be hauled by rail, road, or vessel (ship or barge). It does not include aircraft containers (so-called ULDs or unit load devices). [Link to illustration of ULDs.] It also does not include oversize ocean containers ("sea sheds," used mostly by the military services) which cannot be moved by rail.
The intermodal revolution is generally traced back to experiments by Malcolm McLean (then of the McLean trucking company and later SeaLand) in 1956. The first experiments involved loading some 35 foot highway trailers onto a vessel (the "Ideal X") rather than unloading the contents of the trailer and loading these on the vessel by traditional cargo sling methods.
McLean's experiment quickly showed that there was no need to take the wheels along and that more efficient stowage and handling methods were available if only the box part of the trailer was hauled aboard ship.
This led to the separate container and chassis units-and to the standards for container size and handling hardware that are still in use today.
The most common container sizes used in international commerce are 20 ft, , 28 ft, 40 ft, and 48 ft. Other sizes are 10 ft (used primarily in Europe and by the military services), 24 ft, 44 ft, 45 ft, 46 ft, 53 ft--and probably others I have not yet heard of. As of 2007, the most common containers used in international commerce were 20 and 40 ft, with some 48 ft units.
(Why some of the odd sizes? They are multiples of the cargo pallets on which most goods are loaded into containers. There are also trailer length restrictions in many areas.)
The typical container height is 8 ft 6 inches. So-called high-cube containers are 9 ft 6 in. Some containers of less than 8 ft height are also used for triple-stack shipment of automobiles. (These containers can be triple-stacked on rail cars or double stacked on highway chassis. There are also half-height containers of about four feet for some special-purpose applications.) For information on the relatively new COLTainer® coal containers, see the Recent Developments section at the end.
The standard width of containers used in international commerce is 8 ft (96 inches).
So-called domestic containers, used only for land transport (rail or road) are 53 ft long and 102 inches wide--six inches wider than standard ISO containers. These domestic containers are built to lighter standards, as they are not designed to be exposed to the elements atop a ship at sea. For more about 102-inch wide containers, see the following section.
Please note that these are nominal exterior dimensions. Interior dimensions and particularly door dimensions are smaller. In other words, you would not be able to get an 8x8x8 foot object through the door of a normal ISO container. This is what flat racks (see below) are for.
A movement is underway in Europe for a new container width of 102 inches (8.5 feet); these containers would be classified as belonging to ISO standard 02.
The reason that the European shippers want this dimension is that it would allow two of the standard European pallets to be placed in containers side by side. (Existing containers are based on North American pallet dimensions.)
While the new dimensions would still meet clearances for road and rail transport, the standards are being strongly opposed by international ocean lines, because they have huge investments in current equipment and many have new ships under construction which are completely optimized for current container sizes.
Because containers have useful lives of 15 years or more, these organizations are reluctant to go to any new standard.
Though ships could be reconfigured to carry the wider containers in some deck or hold positions, this would reduce flexibility in loading cargo, because other positions would have to be retained for existing container equipment.
Many transportation organizations are instead pushing for European shippers to go to a different pallet size.
So far there has been no major implementation of the ISO 02 standard. However, APL introduced its own 102-inch wide ocean containers in late 2007. See the update at the end of this document.
Like highway trailers, containers come in many variations. The configurations include simple boxes with end door only and no insulation; insulated; insulated and equipped with temperature regulating equipment (heating/cooling). Temperature control equipment can be internally or externally mounted and use either on-board or external energy sources.
Some special-purpose containers have side as well as end doors. It is also possible for containers to have top doors/hatches, though I have never seen one of these or encountered them in lists of equipment. Some containers have adjustable vents for air circulation, but without any mechanical heating/cooling equipment.
Two special variations are the tank container and the flat rack.
Tank containers consist of a cylindrical tank mounted within a rectangular steel framework with the same dimensions (usually 20 or 28 ft) as other containers. These tanks are intended for use for either liquids or bulk materials. (Because of the weight of liquids and most bulk cargoes, larger sizes are not used for tank containers.)
Flat racks are open-sided platforms, usually with end bulkheads, with the same footprint as basic containers. A collapsible flat rack is one where the end bulkheads can be folded down when the flat rack is stored or shipped empty. Flat racks are used for heavy machinery and are typically carried below decks on ocean legs of their movement.
Containers that are described as 20 ft are normally actually 19 ft 11 in. This simplifies getting two 20 ft containers into the same space as a 40 ft container. (There are similar variations in the actual sizes of many other types of containers. The quoted sizes are "nominal" sizes.)
The framework of containers is normally steel. The exterior sheathing may be either steel or aluminum. Interior sheathing may consist of plywood or composite materials. In 1995 testing began for containers made of space-age composites. Though more expensive than metal-sheathed containers, the composite-sided containers are lighter and are expected to have a longer useful life than metal containers.
Swap bodies, extremely popular in intermodal service in Europe and some other parts of the world, have many of the characteristics of intermodal containers but are not true ISO containers. Swap bodies are in effect half-containers, with that strong bottom that allows them to be transferred from road to rail mode, but only a minimal upper body. In fact, they may be entirely open on top. They have bottom fittings which allow them to be locked onto either a road chassis or a railcar.
With their minimal upper structure, swap bodies cannot be stacked. They can also only be bottom-lifted, using extendable arms on the spreaders of container handling equipment.
Swap bodies should not be confused with flat racks, described in the previous section. Flat racks normally have strong end sections, which allow them to be top-lifted and to be stacked with other containers. Swap bodies have no such end structures.
Often, swap bodies have only a minimal upper metal structure used to support a canvas tarp covering.
000838 Canvas-topped swap-body being lifted by container handler. 000884 Fully-enclosed swap body being lifted.
Both of the above photos were made at intermodal facilities of the Austrian Federal Railways (Österreichische Bundesbahnen or ÖBB) in Austria. Note the extendable arms of the spreader used to bottom-lifted the swap-bodies.Click on the images to view larger versions with more detailed captions.
As a general rule, high density/heavy goods are normally loaded in shorter containers. Low density goods (examples: paper towels, plastics, etc.) are normally loaded in the larger containers. So, when both are loaded, a smaller container will normally weigh more than a larger container.
Some small (20-28 ft) containers are specially rated for extra heavy loadings, having specially reinforced floors and frames. These, however, present problems on inland moves by highway because they may exceed local trailer weight limits when loaded to capacity.
Containers used in interchange among common carriers carry a registration number that identifies the owner and the specific unit. This registration number consists of four letters, the last of which is always "U"--denoting a container--and six numeric digits. A seventh digit is normally used as a CRC check digit.
The alphabetic part of the registration number is compatible with the AAR rolling stock registration. In other words, you would not find a four-character AAR code for a railcar ending in U.
The Official Intermodal Equipment Register contains data on containers owned by the major international ocean carriers, leasing companies, and North American Railroads. (Some of these containers are only approved for land use.)
A downloadable list of reporting marks that includes container identifications is available from the Cyberspace World Railroad and Webville & Hypertext Railroad Web sites which also contains a wide range of other railroad-related data. If you download this very large file to your own computer, you can load it into a word processor and use the word processor's search capability to locate a particular reporting mark.
Containers typically also carry a four digit container type number or code, which should not be confused with the registration number described above.
The type number simply shows that the container fits into a general category, such as 40 ft dry container. There may still be variations in interior fittings and other details.
Links to site with details of container codes |
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This site also contains a downloadable program for decoding container codes. Type in the code and the program tells you the container type. |
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Containers have fittings on top and bottom which assist in their handling and which enable them to be stacked-as much as eight high in terminals and on some ships.
These fittings consist primarily of oval-shaped holes at the lift points. For transport or storage, containers are stacked and connected to each other with IBCs-inter-box connectors. These are pieces of hardware which fit into the oval holes of the container above and below and which are then turned to lock the two together.
Container handling equipment-see a following section on-uses the same fittings.
Some containers can also be handled by oversized forklifts. However, this is generally discouraged because this is more likely to result in damage to the container.
Movement of containers falls into the following areas:
A section is devoted to each of these immediately following.
Highway movement of containers takes place on chassis. (This word is the same whether used in the singular or plural.)
A chassis is a framework equipped with wheels, which, when loaded with a container, results in something very similar to a normal highway trailer.
Chassis are often adjustable--via a telescoping (sliding) center beam which can be locked in multiple positions. So, one type of chassis may be used for both 20 and 28 ft containers; another may be used for any containers between 40 and 48 ft. Adjustable chassis are often called "sliders" by people in the intermodal business.
Chassis have reporting marks that end in Z, just as intermodal trailers that are approved for intermodal loading.
Domestic container (BN Americas) on chassis in Washington State. (Photo by Ernest H. Robl; transparency file no. 940584)
In some cases, containers may make part of their rail movement already loaded on a chassis, just like an intermodal trailer. This may be due to the type of handling facilities available at the loading or unloading point of the rail leg, the availability of chassis at that location, or other factors.
Intermodal operations often move chassis between one terminal and another within a flat rack (see description under container types above). A flat rack can hold up to four collapsed chassis.
[Back to top of Movement of Containers section] [Back to top of document]
Containers of the types described above can be moved by rail by virtually all standard-gauge and broad-gauge systems in the world. Some narrow-gauge (less than 4 ft 8.5 in) lines can also handle containers.
Railcars used for this type of service include both purpose-built cars designed to handle only containers or multi-purpose cars which can also carry highway trailers or other equipment.
Because of differences in loading gauges and operating practices, the equipment used to move containers in North America and Europe is quite different.
Only some North American routes have sufficient clearances to handle stacked containers-one on top of another-in well cars. These cars are called well cars because the center into which the bottom container(s) fit(s) is below the top of the wheels.
Some routes can handle two standard (8 ft 6 in) containers on top of each other; other routes can handle two high cube containers (9 ft 6 in) containers. Routes which meet AAR plate H specifications allow for loaded cars with a maximum height of 20 ft 2 in above the top of the rail.
When different-sized containers are double-stacked on railcars, the smaller container usually goes on the bottom-typically just fitting the well area, while the larger (but lighter) container on top has some overhang.
When a 40/45/48 ft container is combined with two 20 ft containers, the 20s always go on the bottom for two reasons:
The big containers (40/45/48/53/56 ft) have connecting points 40 ft apart (20 ft from the center of the container); you could only connect one end of each of the 20 ft containers. On the other hand, with the two 20s in the well, the well itself keeps the 20s from shifting from side to side. And, both ends of the larger container can be securely connected and supported-one on each end of one of the 20s.
Various combination of the 40 ft or longer containers can be stacked on top of each other in any order as all of these have the connecting points 40 ft apart and can therefore be locked together. The size of the well is obviously a factor, but two other factors are also likely to be considered:
A "Land Bridge" train is one that carries through containers between North American east and west coast ports. For example, an ocean carrier may move container traffic between Asia and Europe in three legs-(1) Container ship Asia to U.S. west coast port; (2) land bridge train to east coast; (3) container ship from east coast to Europe-rather than face vessel size restrictions of the Panama Canal. Modern super container ships do not fit through the canal.
[Back to top of Movement of Containers section] [Back to top of document]
Containers are loaded and unloaded from a medium-sized container ship in the port of Rotterdam, in the Netherlands in Europe. A fuel barge is alongside in the foreground. (Photo by Ernest H. Robl; transparency file no. 930450)
The use of large container ships capable of carrying large numbers of containers and being loaded and unloaded quickly at special container ports has drastically changed the movement of ocean cargo over a relatively short time.
Though most container traffic is on the super container ships between major ports, even most smaller vessels now have provisions for carrying some containers on deck.
On the larger container vessels, the containers you see above deck are only part of the load. A large number of containers are also carried below deck. The container cranes used in major ports to quickly load and unload containers are also capable of lifting off the deck plates of these ships for access to containers below decks.
When stacked on ships, containers are not only locked together with IBCs but also braced with heavy cables, usually in an X-pattern.
Nevertheless, it is not unheard of for a container ship to lose one or more containers overboard in a very severe storm.
Not all container ships are equipped to carry all sizes of containers. Super container ships are typically capable of carrying at least 48/45/40/20 ft containers. Smaller container ships, particularly ones which also carry non-containerized cargo, sometimes may only be able to handle the more common 40 and 20 ft units.
Container capacities of ships are given in TEUs or FEUs. These stand for twenty-foot equivalent units and forty-foot equivalent units. In other words, the TEU number is the total number of 20 ft containers of the standard height the ship is theoretically capable of carrying, though not all parts of the ship may actually be set up for holding 20 ft containers.
Due to so-called vessel-sharing agreements, where carriers pool equipment on a given route, you may find containers of one carrier aboard the vessel of another. Also, in cases where no single carrier serves the entire route of a container's travel, a container may also be interchanged from one ocean carrier to another.
Containers are also often carried inland on barges on navigable rivers.
[Back to top of Movement of Containers section] [Back to top of document]
One of the clever aspects of the container standards is that the required lift and connection fittings allow containers to be handled by both very sophisticated container handling equipment and by very simple equipment. In essence, as long as you have a crane capable of lifting the weight of the loaded container, you can handle the container. In this case, cables with hooks are attached to the four top lift points, coming together at the main hook of the crane. Usually one or more lines are attached to the lower connection points to keep the container from twisting and to manually maneuver it into place at its new location.
This technique is still used at smaller third-world ports where labor is more readily available than complex equipment or when ship-board cranes of smaller vessels have to be used to load and unload containers at smaller ports.
Some mid-range container ships have their own loading and unloading equipment that functions similar to dock-side container cranes. These ships have lifting equipment that runs on overhead rails that extend far enough out over the sides of the ship to be able to lift the containers on and off the dock. This type of equipment is expensive to maintain, however, because, being located atop the ship, the equipment is exposed to the elements while the ship is at sea.
So, most ship to shore transfer of containers involving large container ships and large ports is done with large land-based container cranes.
These cranes lock onto the containers with a piece called a spreader. The reason it's called that is that it can adjust to different lift-point spreads.
These cranes allow very precise placement of containers and can usually also verify the actual weight of each container as it is being lifted (via equipment in the spreader-with this data being sent back through one of the control cables attached to the spreader).
Containers are normally not transferred directly from a ship to a railcar, though there are some exceptions. The reason for this is that the most logical sequence for unloading a container ship (which has to remain in balance!) may not match with the most logical sequence for loading a double-stack train. Additionally, containers from one ship may go on different trains to different destinations.
Similarly, trains reaching a port may carry containers destined for different locations-which are served by different ships, or which, at the very least, need to be loaded on a ship in a very specific sequence.
So, there is usually a rail intermodal terminal close to the actual dock, with transfers being made on a road chassis. Containers may be stored in transit on the chassis or stacked several-high.
The equipment at a port-adjacent intermodal rail facility is much the same as at inland intermodal facilities where containers and trailers are moved on and off intermodal trains. The equipment falls into two general categories-straddle cranes which span one or more tracks and paved areas for chassis placement and side-loaders. Straddle cranes may operate on fixed rails or with large rubber tires.
A Union Pacific side-loader lifts a container from a TTX flatcar at the small intermodal facility at UP's headquarters city of Omaha, Neb. The loader has locked onto the corners of this 40-foot container with its spreader. (Photo by Ernest H. Robl; transparency file no.: 900452)
Smaller intermodal facilities often have only side-loaders because straddle cranes are very expensive and require a lot of operating space. Side loaders resemble oversized fork-lifts, but are normally equipped with spreaders, so that the containers are actually picked up by their top lift points. They have telescoping columns so that they can stack containers three or four high for intermediate storage.
000882 Kalmar reachstacker container cranes awaiting work assignments, showing their spreader assemblies.. 000895 Kalmar reachstacker maneuvering with P&O container after having lifted it from a chassis.
Both of the above photos were made at intermodal facilities of the Austrian Federal Railways (Österreichische Bundesbahnen or ÖBB) in Austria.Click on the images to view larger versions with more detailed captions.
[Back to top of Movement of Containers section] [Back to top of document]
Like railcars, containers may be interchanged among carriers of the same mode or of different modes. (In this context, interchange simply means that the container goes from the custody of one carrier to the custody of another carrier at a specified location.) There are rules that govern the interchange of containers, just as is the case for railcars.
Containers may be interchanged with or without the railcar (or chassis) that it arrives on. For example, a container bound from Long Beach, Calif., for Cleveland, Ohio, may arrive in Chicago on railroad A, be unloaded onto a chassis and be moved by drayage (truck-haul) to the intermodal facility of railroad B, where it is loaded onto another railcar for the final move. This is simpler than trying to pull apart of the consist of a dedicated intermodal train, which consists of multiple linked platforms.
Containers may also make different legs of an ocean move on the vessels of different carriers. For example, a container moving from Europe to an island in the West Indies (Caribbean) may move from Europe to Jacksonville, Fla., on the vessel of a major carrier. It may then make the final leg on a smaller vessel belonging to a different carrier.
| In North America, interchange of intermodal equipment is governed by the Uniform Intermodal Interchange and Facilities Access Agreement (UIIA). This agreement is administered by the Intermodal Association of North America (IANA). IANA has a site at which a copy of this document is accessible in PDF format for downloading and printing. To go to the download page, click here. This contract covers liabilities and other issues for participating organizations. |
[Back to top of Movement of Containers section] [Back to top of document]
The intermodal scene continues to change as new concepts are tried out and as regulations which sometimes limit types of equipment are revised. This section highlights noteworthy developments related to intermodal containers. Currently, there are the following subsections:
This section does not pretend to be an all-inclusive news report on intermodal developments.
An unusual intermodal operation exists in U.S. state of Alabama, where coal is supplied to a power plant by a combination of rail and highway moves. Rather than transloading the coal, the coal is loaded into special open-top intermodal containers (with an end dump-gate) which are transferred between railcars and highway trucks equipped with hydraulic end dumping equipment. The rail movement is provided by Norfolk Southern.
The containers are called COLTainers®, but could also be used for other types of aggregates.
This operation was described in the January, 1997, issue of the magazine Railfan and Railroad.
A previous link to COLTainer information on the NS Web site which had been provided at this location has been deleted because NS removed the applicable information from its Web site.
Containers are carried on single-level railcars. They could, however, be stacked for empty shipment or empty storage because they have standard intermodal container fittings.
In late 1996, the German Railways (Deutsche Bahn or DB) announced a demonstration version of what amounts to diesel multiple unit trains for containers.
(Note: The DB pages linked to in the preceding paragraph contain information on DB's freight operations in German only. The site does not currently contain specific information about the project described in this section.)
This concept, called the CargoSprinter, consisted of multiple platforms, the end ones of each group are powered by a small diesel motor but which also can carry up to two 20 ft containers. The intermediate platforms are unpowered. The end platforms have a control cab, in addition to the cargo space.
Several of these trains could be linked together and run in MU configuration with a single operator.
These trains were designed to provide rapid service by rail between smaller container terminals and to provide competition for highway trucks.
This equipment was described and illustrated in the January, 1997, issue of Railway Age (p. 76).
This concept ultimately proved unsuccessful, not for technical but for economic reasons. Because it was produced in small numbers, the specialized equipment was expensive to maintain as all the container flats in the train had to have multiple-unit (MU) control cables. At the same time, because of capacity limitations of the fixed consist, the equipment could only be used on a few routes.
The DB decided to abandon use of this equipment in 2004. But, it was concerned that it might be used by a competing rail entity, so most of the remaining CargoSprinter equipment was sold to the Austrian Federal Railways for use in maintenance of way activities. The self-propelled trains will carry a range of maintenance of way equipment in a modular configuration that can be lifted on and off the former container flats.
In November of 2007, APL (formerly American President Lines) a major player in the international intermodal business and owner and operator of a large fleet of container ships, began trans-Pacific service with 53-foot ocean containers.
Like the so-called domestic containers used in North America for many years, these containers are also 102 inches wide--six inches wider than ISO containers.
Like the 53-foot domestic containers, the 53-foot ocean containers are designed to carry bulky but low-density goods (low weight per cubic foot). Examples of this type of cargo include paper towels and stuffed toys. The new APL containers are built stronger, however, to help them hold up to the stresses of repeated ocean voyages. Therefore, they have a higher tare weight than domestic containers. They can also be stacked higher than domestic containers.
Initially, these new ocean containers are being used only by APL, as they do not comply with any international standard. However, it is quite likely that these containers will also be adopted by other ocean carriers, particularly those which have vessel-sharing agreements with APL. APL reported high demand for the new service, once it was announced to customers.
The use of the new larger ocean containers should not require any major changes at ports or inland terminals, as equipment capable of handling 53-foot domestic containers should also be able to handle the slightly heavier ocean containers. Similarly, these containers should also fit onto railcars and chassis capable of carrying 53-foot domestic containers. With low-density cargo, the slightly heavier ocean containers should still comply with highway weight limits when the containers are moved by chassis.
Why the larger containers? Increased efficiency. If more cargo--at least by volume--is carried in fewer containers, this requires fewer lifts at ports and inland terminals. Ships can be loaded or unloaded faster, with less dwell time in ports. Ships only earn money when they are moving cargo, not when they are sitting in ports.
Actually, some 53-foot containers have always moved by ship, but this was usually a one-time empty journey in a protected position on the ship. Why? Because most of the domestic containers used in North America are actually manufactured in Asia, and moving them by ship is the only practical way to get them to North America.
Now available from Ernest H. Robl, a handy book that includes the information on this page and much more:
By Ernest H. Robl
For additional information, including an extensive description, the table of contents, and sample content, click on the title above.
Published November, 2002. 180 pages; more than four dozen illustrations.
Comments, corrections, and additions are welcome. I do, however, want to keep this to a manageable length.
A wide range of transportation information that didn't quite fit into this page has been included in my intermodal book. See the section above.
Two major trade associations involved in promoting intermodal traffic are
North America |
Europe |
Another site that may be of interest is that of Sea Box Inc., a company that custom-builds and adapts containers for special-purpose applications.
In addition to being a freelance photographer/writer specializing in transportation, I once worked for a company involved in producing software for the transportation and logistics industries. At that time, this company, Encompass, was jointly owned by a major airline holding company (AMR, parent of American Airlines) and a major railroad/intermodal carrier (CSX). None of the above information reflects or pretends to be any official information of either Encompass or its owning partners.
All information is offered for general background and is subject to change. It is therefore provided without warranty or guarantee of any kind.
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