The modern open-top hopper cars are a bit more sophisticated than what they might look! While these railroad freight cars today almost always haul coal or varying forms of aggregates, such as ballasting (a term which refers to the crushed rock used under the railroad tracks that acts as support and cushioning), coal, or iron ore they have a number of different drop-bottoms to empty their cargo. You may then be asking, “What in the heck is the difference between gondolas and hoppers?” The drop-bottoms are basically what separate the two car types. Whereas gondolas can look just like hoppers, right down to their size, length, commodity, and even a basic form of drop-bottoms as well (which discharges material straight down), the difference that separates them, is that hoppers contain some type of angled or sloped drop-bottom chutes or hatches, which use the force of gravity to quickly unload their cargo without having to tilt or turn the car upside down in any way.
The hopper car can trace its roots all the back to the very beginning of the railroad industry itself, being used as early as the late 1820s by the Delaware & Hudson Canal Company to move coal, which hasn’t changed too much over the last three centuries! Back then, however, the cars were not known as hoppers but jimmies, although they did carry all of the basic features that differentiate the car from its companions of today. Over the years, as with all railroad freight cars, the hopper became larger and stronger (moving from wood and wood-steel construction to all-steel construction) able to haul heavier and heavier loads (which allowed for better efficiencies and thus, better ROI). For instance, during the United States Railroad Association’s reign during World War I, as with the 40-foot boxcar the hopper became standardized with the 55-ton version.
As the hopper became larger so did the number of drop-bottom chutes it carried; from two, to three, and now today most carry four chutes (more chutes allow for faster unloading times). Similarly, what has allowed the increased number of chutes on a hopper is mostly the result of its increase in size from 50 tons to today’s 100-ton capacity, which is the size most commonly used by the railroads today. Today’s hopper car has come a long way, even from the USRA 55-ton standardized car of the early 20th century. Not only are the current cars carrying 100-tons but also many now have rotary couplings to literally spin the car 360 degrees while still attached to the train to empty its cargo.
Other variations include covered hoppers, which carry bulk products such as grain, lime, cement, and sand that must be protected from the weather while in transit. Interestingly, the history of this car can be traced back to the earliest days of the industry as well and roughly ten years after the open hopper first went into service. The first covered hopper design is said to have been used in the 1830s to haul, as mentioned above, grain and prevent its exposure from the elements. The car had open hatches on the roof as well as on the bottom for loading and removal. Surprisingly, though, as Mike Schafer notes in his book "Freight Train Cars" railroads were slow to use the covered hopper. They found that the redundancy offered by the ubiquitous boxcar, which could handle everything from cars to paper, could do the job just as well.
Widespread use of the covered hopper did not begin until after World War II and particularly in the 1960s and 1970s. Today, aside from the products already mentioned the car carries flour, plastic pellets, potash (fertilizer), fishmeal, and soybeans. Ore jennies are yet another type and these little cars get their size for a reason. They are built specifically for hauling taconite pellets (iron ore) which are much more dense (i.e. heavier) than most other types of bulk materials like coal and stone, which gives the car their small, but effective size (these cars are predominantly found in the northwest Great Lake region, such as Minnesota and Michigan where large concentrations of iron ore continues to be mined).
The history of the jenny can likely be traced to around the mid-1800s although as Mr. Schafer mentions in his book its widespread use did not begin until towards the end of that century when iron became commonly produced. Soon after the production of much stronger steel continued the need for the product. In most ways the ore jenny is simply a miniature hopper, which could be found in service on most of the large upper Midwest railroads at the time including the Milwaukee Road, Chicago & North Western, Bessemer & Lake Erie, Missabe Road, Soo Line/Duluth, South Shore & Atlantic, Lake Superior & Ishpeming, and Escanaba & Lake Superior. As the years go by the hopper car will undoubtedly become larger and more sophisticated. However, regardless of the changes it will go through, the car will be just as recognizable 50 years from now as it was 50 years ago, a platform capable of discharging a product quickly through bottom, angled chutes.
For more reading about hopper cars consider the book, Freight Train Cars, from Mike Schafer, one of the leading authors covering all corners of the railroad industry (from its history to present day operations). The book gives an excellent general history and overview on all of the common freight car types and if you are interested in learning more about them, or you are simply looking to better understanding their history and development you should very much enjoy Mr. Schafer’s book. If you're interested in perhaps purchasing this book please visit the link below which will take you to ordering information through Amazon.com, the trusted online shopping network.