Milk cars are a specialized type of railroad car

Railroad car

A railroad car or railway vehicle , also known as a bogie in Indian English, is a vehicle on a rail transport system that is used for the carrying of cargo or passengers. Cars can be coupled together into a train and hauled by one or more locomotives...

 intended to transport raw milk

Milk

Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

 from collection points near dairy

Dairy

A dairy is a business enterprise established for the harvesting of animal milk—mostly from cows or goats, but also from buffalo, sheep, horses or camels —for human consumption. A dairy is typically located on a dedicated dairy farm or section of a multi-purpose farm that is concerned...

 farms to a processing creamery

Creamery

In a dairy, the creamery is the location of cream processing. Cream is separated from whole milk; pasteurization is done to the skimmed milk and cream separately. Whole milk for sale has had some cream returned to the skimmed milk....

. Some milk cars were intended for loading with multiple cans of milk, while others were designed with a single tank for bulk loading.

Origins

Milk has long been a staple food of agricultural societies. Fresh milk sours quickly if kept warm. Railways were used as early as 1840 to rapidly transport fresh milk from farms to cities. Early milk transport was in covered, tin-plated steel cans containing about 10 gallons (40 liters). Passenger trains typically offered the fastest service, so milk cans might have first been loaded into baggage car

Baggage car

A baggage car or luggage van is a type of railway vehicle often forming part of the composition of passenger trains and used to carry passengers' checked baggage, as well as parcels . Being typically coupled at the front of the train behind the locomotive, this type of car is sometimes described...

s. A farmer would adjust his herd milking schedule to have the milk cans filled shortly before scheduled arrival of the train. When multiple farmers required shipment, a separate car might be carried by the train specifically for milk cans; and that car could be delivered directly to the creamery to minimize time required for intermediate handling of the milk cans with other baggage. Once the handling advantages of a separate car were recognized, milk cars were built with insulation

Thermal insulation

Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

 to reduce warming during transit and the milk cans might be packed in ice

Ice

Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

 during warm weather. A few milk cars were built or retrofitted with mechanical refrigeration

Refrigeration

Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...

 following World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

.

Tank cars for bulk loading

Increased availability of motor vehicle

Motor vehicle

A motor vehicle or road vehicle is a self-propelled wheeled vehicle that does not operate on rails, such as trains or trolleys. The vehicle propulsion is provided by an engine or motor, usually by an internal combustion engine, or an electric motor, or some combination of the two, such as hybrid...

s after World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 encouraged bulk transport of milk to minimize inefficient handling, washing and redistribution of milk cans. Milk tank car

Tank car

A tank car is a type of railroad rolling stock designed to transport liquid and gaseous commodities.-Timeline:...

s were first made of glass-lined steel, and later of stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

. These tanks were often enclosed for insulation within a car body resembling a boxcar

Boxcar

A boxcar is a railroad car that is enclosed and generally used to carry general freight. The boxcar, while not the simplest freight car design, is probably the most versatile, since it can carry most loads...

. These tank cars were usually filled with milk pre-cooled to 38° F (3° C) at a central collection point just prior to pickup by a milk train with a delivery schedule avoiding need for additional cooling during transit.

Peak use and decline

Large cities in the eastern United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 encouraged nearby rural areas to specialize in production of milk. Railroads connecting these rural areas to cities scheduled daily milk trains (sometimes called milk runs) to pick up loaded milk cars from collection points along their route. These trains sometimes carried a mail car

Railway post office

In the United States a railway post office, commonly abbreviated as RPO, was a railroad car that was normally operated in passenger service as a means to sort mail en route, in order to speed delivery. The RPO was staffed by highly trained Railway Mail Service postal clerks, and was off-limits to...

 and a passenger car. These were often the last scheduled passenger trains serving those rural areas. Rail transport of milk peaked in the 1930s; and most milk was traveling in highway trucks by 1960.