For the first 100 years of their operation, railroad tank cars were adapted to many different commodities. Like other cars on the rails, size and capacities remained relatively small. Beginning in the 1960s, as railroads adopted larger car footprints for other rolling stock, the idea of producing larger tank cars for bulk shipments presented new opportunities.
The engineering of larger “super tank cars” was by no means coincidental. Railroads were facing increased competition from new federally-funded pipelines and inter-coastal waterways for petroleum traffic. The older 10,000 to 13,000 gallon tank cars just couldn’t keep up.
The 1960s saw the construction of the largest tank cars in history. The major tank car builders and leasers, as well as the Pennsylvania Railroad, built experimental prototypes to test construction theories and entice shippers. Much like shopping for groceries in a wholesale outlet, shipping in bulk allowed railroads to offer reduced rates to large customers.
In 1963, Union Tank Car built the first prototype with a 50,000 gallon capacity. Aside from its large capacity, the car featured a new dual-diameter tank commonly called a whale-belly for its distinct shape and low center of gravity. The record goes to General American (GATX) with their 60,000 gallon (272,700 lb capacity) monster built in 1965. The experimental 97′ car was simply too big for many curves and its service life was short lived.
The Pennsylvania Railroad built two 36,000 gallon prototype cars in 1966. Nicknamed “Rail Whales” through an employee contest, there were one pressurized and one non-pressurized car. While much smaller than the other prototypes, these cars are clear predecessors to many of the more standardized 33,000 gallon cars which have since become common.
While these largest of designs were not repeated, over the next four years just over 800 additional super-sized tanks hit the rails. Most were built in small orders and specialized for a wide variety of commodities. Oil and chemical companies both used the cars with common routes including travel between Gulf of Mexico ports to refineries in the Mid-Atlantic. These cars used a variety of construction techniques including multiple trucks connected by span-bolsters – a practice normally associated with heavy-duty flat cars.
The era of big tank construction came to an end in 1970 when regulations limited the size of tank construction to a mere 34,500 gallons. In addition to the obvious safety concerns in the event of accidents, railroads found much more routine issues with wear on track, limited service routes due to clearances and a simple lack of customer demand for cars that large. The construction and overall operating costs of a pair of typical 23,000 gallon cars were not much greater than a single 46,ooo gallon car but offered much better utility. Existing cars of greater capacity were allowed to remain in service however and many did into the 1990s. About 1/4 of the total built were rebuilt into cars of lesser capacity.
Two of the prototype super tankers have been preserved in museums today. Pennsylvania 500001 can be seen at the Railroad Museum of Pennsylvania and GATX 96500 is on display at the Museum of Transportation in St. Louis. UTLX’s prototype had been preserved but was badly damaged by Hurricane Ike and scrapped in 2008. A small group of super tank cars still remain active and have just a few more years left until mandatory retirement.
Today the largest cars typically in service are 33,000 gallons – used mostly for liquefied petroleum gas and anhydrous ammonia. Of course there are many smaller varieties as well with different commodities and shippers requiring their own special needs.