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. History 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 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