An autorack, also known as an auto carrier (also car transporter outside the US), is a specialized piece of railroad rolling stock used to transport automobiles and light trucks. Autoracks are used to transport new vehicles from factories to automotive distributors, and to transport passengers' vehicles in car shuttles and motorail services, such as Amtrak's Auto Train route.

In the early 20th century, when automobiles were still new technology, their production levels were low enough that they could be shipped in sufficient quantities in boxcars. Two to four automobiles would usually fit into one boxcar. But as the automobile industry grew in size, railroads found that they needed to modify the boxcars for more efficient loading. Some modifications included longer boxcars, larger sliding double side doors located near one end of the boxcar, or doors located on the boxcar ends.

These modifications helped, but the demand for new automobiles outpaced the railroads' abilities to build and modify boxcars in which to ship them. In 1923, the Grand Trunk Western Railroad experimented with modifying a group of 61-foot-long (18.59 m) wood-frame flat cars to increase their capacity by adding collapsible frames to allow for double-deck operation. The concept was not perfected and therefore failed to gain acceptance. In the 1940s and 1950s, some railroads experimented with automobile-loading assemblies that would lift one or more automobiles above others within a boxcar. The success of these assemblies was limited due to their special use and specific size; it proved uneconomical to maintain a fleet of these assemblies that could only be loaded into boxcars from the ends of the cars.

By this time, in the United States, most circuses still traveled by rail. Circuses were major haulers of wheeled vehicles, carrying all of their vehicles on flat cars, usually behind their own passenger cars or in separate sections of their trains; basically, one train would haul the performers and employees while a second train would haul the vehicles and freight. The circus solution to loading vehicles was to use a string of flatcars. A temporary ramp was placed at the end of the flatcars and temporary bridge plates spanned the gaps between adjacent flatcars; the road vehicles were driven or towed up onto one car and then driven or towed down the train. This type of vehicle loading became known as "circus style" due to its frequent use by circuses.

In the 1950s, most railroads took the cue from circuses and started loading their own flatcars in this manner. But, loading even up to six automobiles onto one flat car left a large amount of space above the vehicles that was unused. The natural solution was to take the temporary assemblies that were used to stack and load vehicles within boxcars and permanently attach them to the flatcars. The assemblies, also called racks, created two levels on which automobiles could be loaded. To complete the flatcar, foldaway bridges were added to the ends of the flatcar decks to allow the vehicles to be driven the entire length of a train for loading. Such flatcars eliminated the need for specialized equipment to load and unload boxcar racks. All they needed now was a ramp at the right height.

In the mid-1950s, in Germany, Volkswagen Beetle production was increasing beyond the capacity of highway trucks (autocarriers). Volkswagen engineers worked with German railroads to design a railroad car that was basically an extra long version of a vehicle hauling trailer. The design they came up with was able to carry 10 vehicles on one car. VW's two-level flatcar design effectively became the first autorack, entering service circa 1954.

Also in 1954, Evans Products, a manufacturer of loading racks for carrying automobiles in conventional boxcars, developed a bi-level Auto-Loader superstructure with an elevating top deck capable of carrying six cars or light trucks on a typical flatcar. Two prototype units were constructed and mounted on conventional 53 ft (16 m) flat cars for field testing. NYC 500085 carried a semi-streamlined rack, while UP 5800 had a more utilitarian rack mounted. Neither design went into commercial production.

In 1956, Canadian National (CN) introduced an innovative group of bi-level auto carriers. These CN cars were similar to conventional boxcars, except they had a second floor and doors at both ends of the car instead of the usual side doors. They were huge by the standards of the time; the cars were 75 ft (22.86 m) long and could carry eight vehicles. These cars were a big success and helped lead to the development of today's enclosed auto racks.