"In 1999 Gunderson (a subsidy of Greenbrier Inc.) began producing a revolutionary new car that is at the cutting edge of railroad technology. With the catchy name, Auto-Max, these cars are unmistakable and have been turning the heads of both railfans and model railroaders alike. The sheer mass of this two-unit articulated car has all the subtly of a rolling barn. At 20' 2" tall and 145' 4" long, this is one of the largest car on the rails today.
The real driving force behind the development of a car of such huge proportions is the popularity of Sport Utility Vehicles. Practically since the development of the rack on flatcar, "Autoracks" have come in two versions. The Bi-Level is intended for large trucks and vans while the Tri-Level is intended for sedans and other small vehicles. But most SUV's fit in the gray are between the cars and trucks. Before Auto-Max, SUV's were put in Bi-Levels and represented a lot of wasted clearance room. Because Auto-Max uses most of the railroad clearance diagram, it can actually load three levels of SUV's in one railroad car. In other words, the Auto-Max can cram in 22 SUV's while a standard Bi-Level can only hold a mere 10. Even Thrall's new articulated Bi-Level car can only handle 16 vehicles
For more information refer to the article and drawings on pages 126-130 of the November 1999 issue of Model Railroader Magazine."
http://www.trainweb.org/funnelfan/automax.htm