The coaches were of a unique, split-level design, with the center portion of each car having a floor level two feet below that of standard coaches. This lowered the cars' center of gravity, allowing the train to safely take curves at higher speeds. The coaches were also built to a stressed-skin "Tubular" design, with the shell of the car providing all of the cars structural strength, without the normal heavy steel underframe. This resulted in cars weighing only 60% of what standard cars would weigh.
The split-level design, with short stairways between levels, proved unpopular with passengers, causing bottlenecks during loading and unloading.
The Pennsylvania introduced the cars in 1956, with the set making two daily round-trips between New York City and Washington, D.C.. These services were named Morning Keystone, Midday Keystone, Evening Keystone, and Midnight Keystone. In addition to the tubular coaches all four trains operated with conventional equipment such as dining cars and parlor cars. The Midnight Keystone, which departed New York at 11:10 PM, carried sleeping cars.
The train set was retired from service in 1968 and stored in Altoona, Pennsylvania.Amtrak took possession of the equipment but sold it to the South East Michigan Transportation Authority (SEMTA) in May 1976 for $80,000.
^Simon, Elbert; Warner, David C. (2011). Amtrak by the numbers: a comprehensive passenger car and motive power roster, 1971-2011. Kansas City, MO: White River Productions. p. 153. ISBN978-1-932804-12-9. OCLC837623640.