Intermodal equipment

Flatcars and well cars; containers and trailers
For twenty years after its introduction in 1961, the 89-foot flatcar was the workhorse of the intermodal freight-car fleet. Carrying two standard 40-foot trailers or their container equivalents, the 89-foot car was admirably suited to the railroads' needs - that is, until the state and federal governments began increasing the maximumn length of trailers permitted on the highways. As trailers and containers have grown longer and wider, railroads, car owners, and carbuilders serving the intermodal market have had to scramble to keep up, accounting for the various types of equipment seen today.

But before we look at the various types of intermodal cars found on railroads today, let's examine what they're hauling: the trailers and containers.

The boxcar's successor

About 1.4 million trailers and containers are listed in the Uniform Machine Language Equipment Register maintained by the Association of American Railroads. This is a computerized repository of data on equipment used in rail service. Many additional trailers and containers are used by motor and ocean carriers but not listed in UMLER. By one estimate, over 8.3 million containers are operating worldwide, and many turn up on railroad cars. The number of intermodal units greatly exceeds the 1.2 million or so cars listed in UMLER.

Railroads control a relatively small portion of the intermodal trailer and container fleet. Only about 33,000 trailers and 33,000 containers bear the reporting marks of Class 1 and regional carriers. Short lines manage another 11,000 trailers, primarily to earn per diem payments from the larger lines. Leasing companies such as Transamerican and XTRA supply another 53,000 trailers and containers for rail use.


Traditionally, trailers built for rail service had to be constructed to sturdier specifications than highway trailers. Heavier construction was necessary to contain load shifts due to slack action or impacts with other cars in switching operations - forces not normally experienced in highway service. Railroad trailers also needed lifting pads to survive mechanized loading. Of course, these trailers weighed more than highway trailers, thus reducing the amount of payload they could carry, and they cost more, too.

But that's no longer true. Over the past 10 years, most railroads began operating dedicated intermodal trains using mostly articulated equipment, which reduced slack and switching. Because their operating environment has become friendlier, new railroad trailers are not built much differently from their highway cousins. Highway trailers, meanwhile, have become common loads on railroad cars.

Trailers differ mainly in length and width, and both dimensions are influenced by a mass of federal and state laws that regulate vehicle size and weight.

The growth of the typical piggyback trailer from 35 feet in length during the 1950s to 40 feet in the 1960s and '70s, to 45 feet in the 1980s tracked the steady liberalization of state restrictions on truck size. In 1983 the federal government told states they could not outlaw the operation of single trailers shorter than 48 feet, or two-trailer combinations shorter than 56 feet (28 feet per trailer). Subsequently, all the states passed laws allowing operation of single trailers up to 53 feet long, and 12 states permit 57-foot trailers. The 1983 federal law also increased the minimum restriction on trailer width from 96 to 102 inches.

Common trailer lengths today are 28, 45, 48, 53, and 57 feet. The 28-foot units have a single axle and are favored by United Parcel Service and less-than-truckload carriers, which hook them together in three-unit combinations for highway operation where state law allows.

Most railroad-controlled trailers are 45 feet long; two 45-footers are the largest pair that can be loaded on the standard 89-foot intermodal flatcar. Truckload carriers like J. B. Hunt and Schneider National provide most of the trailers that exceed 48 feet in length. Most trailers built since 1982 are 102 inches wide, while interior height ranges up to 110 inches.

Trailers with level floors and no heaters or refrigerators (known as "dry vans") predominate. "Reefer" units have diesel-powered heating and cooling units for temperature-sensitive cargo. "Flatbed" trailers, like flatcars, haul loads that do not need protection from the weather. A few "drop frame" trailers with small wheels and low floors in back of the kingpin (where the trailer joins a tractor or is secured to a railroad car) and "open top" trailers that run covered with tarps complete the fleet.


Piggyback began with trailers because the basic trailer design had become accepted in the marketplace and "circus loading" of trailers required minimal investment in terminals. In the 1950s, though, trucker Malcolm McLean developed the concept of the intermodal container: a steel box that could be moved from ship to rail to truck without unloading.

While the container concept was briefly embraced by a few railroads during the 1960s, it did not take off until the railroads installed mechanized loaders in their major terminals and closed their circus ramps in the 1980s. The double-stack well cars that entered service about the same time greatly improved the economics of container transportation by rail. Today the railroads move more containers than trailers, and container traffic is growing at a faster rate.

There are two types of containers: international and domestic. Containers built for international service must conform to design and length standards established by the International Standards Organization. This enables ocean carriers to stack them together on ships, or railroads to load them on flatcars, regardless of ownership or country of origin.

International containers are either 20, 40, or 45 feet long, The shorter 20-foot boxes generally will carry heavy-loading commodities, such as machinery or fasteners (nuts, bolts, screws, washers), in deference to crane capacities and highway load limits, while lighter goods travel in the more-common 40-foot boxes.

Containers in domestic use function like trailers without wheels. They come in the same lengths as trailers: 28, 45, 48, or 53 feet. Dry van containers are the most common, but open-top, flatbed, reefer, and tank varieties can be seen as well.

Loading containers on stack cars is harder than it looks. Not only must the length of each box be considered, but also its configuration and weight and the carrying capacity of the railroad cars, which can vary. A pair of 20-foot containers, for example, may weigh enough to load one well to its capacity, while the next well may be under capacity with a 53-foot container of down coats on top of a 48-foot container of toys.

Twenty-foot containers cannot be loaded over a 40-foot or longer container because the longer boxes do not have fittings in the middle of the roof for the interbox connectors that hold stacked containers together. But newer intermodal cars, like TTX's 56-foot single-well cars, are designed to handle four 28-foot domestic containers, stacked two on two.

Chassis, or special flatbed trailers, are used to ferry containers between rail terminals and customers or, in many cases ocean carriers. These come in lengths that correspond either to 20-foot or 40-foot and longer boxes, and many can adjust to take containers of different lengths.

One of the most difficult tasks in intermodal transportation is distributing chassis to ensure there are enough at each terminal to handle the available business, but not too many. Occasionally a railroad may ship a chassis loaded with a container like a trailer, but the widespread acceptance of double-stack equipment has made such moves increasingly rare.

Railroads haul intermodal equipment in two types of cars: flatcars and well cars.


Many 89-foot flatcars (or "pigs," for their role in piggyback service) are still in service, but most of the survivors have been modified to tote two 45-foot trailers - or have been reequipped as two- or three-level to carry auto racks.

Some railroads, including Chicago & North Western, Santa Fe, and Norfolk Southern, converted excess 50-foot boxcars and 100-ton bulkhead flatcars to handle 45-foot and 48-foot trailers during the early 1980s, but these efforts resulted in cars that were heavier, and thus less efficient, than half of an 89-foot flatcar.

Lightweight cars carrying one of the longer trailers on European-style single-axle trucks were tried too; examples of both types of cars remain in regular use.

More recently, pairs of 89-foot flatcars have been joined together with drawbars to handle three of these long trailers, with the middle one loaded over the drawbar; some 1200 pairs are roaming the rails.

But to satisfy customer demand for better ride quality, as well as the railroads' desire to reduce maintenance costs and tare weight (thus fuel consumption), the industry turned to articulated designs to haul most of the new highway equipment.

Articulated intermodal cars - that is, cars with separate load-bearing units resting on common trucks - were initially developed by the Santa Fe in the late 1970s. By eliminating several sets of trucks and couplers, and reducing the carbody to a steel center sill with hitches and wheel supports, the "spine car" design both saved weight and reduced slack action, providing a smoother ride.

Contemporary spine cars have units capable of handling trailers or containers up to 53 feet long, most commonly in a five-platform configuration.

Well cars

Double-stack cars, or well cars, for container shipments were introduced by the Southern Pacific also in the late 1970's. However, the rest of the industry was slow to embrace the double-stack concept, which often required expensive programs to eliminate clearance restrictions, and did so only after American President Lines developed a network of stack trains spanning the continent, beginning in 1984.

These double-stack cars combine the ride-enhancing qualities of articulation with the efficiency inherent in transporting containers two-high. They permit railroads to carry containers, which historically generated low yields, in profitable quantities without costly siding extensions.

Early double-stack well cars employed bulkheads to secure the top row of containers, but substantially all cars built since the mid-1980s rely on interbox connectors to hold the containers in place, just as on ships.

At first wells were uniformly sized for 40-foot containers, but subsequently, cars with wells for 45- and 48-foot containers were developed. Engineers are currently working on a design for a 53-foot double-stack car to fit within the present clearance diagram, but many existing cars can handle 53-foot containers on top of shorter boxes inside the wells.

Single-well and drawbar-connected multiple-well cars have been developed to transport heavy containers; they provide more wheels to distribute the extra weight.

The demarcation between single-stack spine and double-stack well cars is blurred by the "all-purpose" well car first delivered to NS. To increase flexibility, these cars are equipped with hitches and can carry either a single trailer, a pair of 28-foot "pup" trailers carried back-to-back, or stacked containers in each well. Because of the preference of many over-the-road truckers for 28-foot trailers, more new car designs to accommodate this equipment efficiently are on the way.

Other types of indermodal equipment

Triple Crown Services, a motor carrier subsidiary of Norfolk Southern, is the principal advocate of RoadRailer intermodal equipment, which dispenses with cars altogether to reduce terminal costs. Amtrak, Burlington Northern Santa Fe, and Canadian National also provide intermodal transportation with RoadRailers.

Canadian Pacific uses the "Iron Highway," a double-ended trainset that splits in the middle to permit circus-style unloading of trailers at low-volume points without expensive terminal investments.
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