The Keystone was a set of eight lightweight streamlined cars built by the Budd Company in 1956 for the Pennsylvania Railroad.

The set comprised seven coaches seating a total of 574 passengers and a single head end power (HEP) generator car.

This lowered the cars' center of gravity, allowing the train to safely take curves at higher speeds.

[2] The split-level design, with short stairways between levels, proved unpopular with passengers, causing bottlenecks during loading and unloading.

[3] The Pennsylvania introduced the cars in 1956, with the set making two daily round-trips between New York City and Washington, D.C.