From the record
“The Abraham Lincoln, also known as Denver and Rio Grande Western Railroad Business Car No. 101, is the oldest operable passenger car in the United States allowed to run on tracks operated by Amtrak. It is listed on the National Register of Historic Places.”
Wikipedia article Abraham Lincoln (Pullman car), CC BY-SA 4.0.
One of 13 National Register listings published here for Adams County · listed in 1988 · category: Object.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service