Deluxe Innovations Gunderson Twinstack 5 unit articulated car. TTX Yellow.

Of all the intermodal designs that have been offered to the railroads, the Gunderson Twinstack is the most colorful and unique of the lot. Purchased by more owners than any other, the Twinstacks joined the Thrall Lo-Pac 2000 as the cars that made intermodal containerism work. This car is an evolution of the design developed by Southern Pacific and ACF to carry 10 40' containers across the United States "land bridge" for Sealand Corporation in the early eighties. The articulated design concept was developed to 1) save length, 2) save weight to minimize fuel consumption, and 3) decrease slack runout to minimize damage to the cargo. Obviously the concept is very successful, as it is the fastest growing segment of rail transit today.
1985 was a pivotal year for Gunderson and the Bulkhead-style stack car. The success of the ACF/SP experiment lead to the production of a 1984 prototype for the Twinstack, and 1985 full scale production. First deliveries were made to Greenbrier Leasing and the NYSW for Sealand service. Over the course of the next three years, 876 cars were built with a total of 4,370 wells. In 1988, Gunderson switched to the Maxistack design, and the bulkhead era came to a close.
Many railroads owned cars themselves, but the majority were owned by Trailer Train Corp. and assigned to service on a particular railroad. Southern Pacific, Burlington Northern, and Santa Fe all had Trailer Train Yellow carsets with their logo and slogan and TT reporting marks. These cars are currently running with the original paint scheme, a modified TT paint scheme or a full TTX repaint. You will also find the original Sealand/NYSW cars running today with CSXT reporting marks. Many of the Southern Pacific, Santa Fe, and Burlington Northern cars are still running in their original colors.
The Twinstack has proven to be a very durable car. No cars have been reported "retired" due to fatigue, although some have been wrecked. The bulkhead equipment seems to have more torsional rigidity than some other designs, so should last well into the future.