Railway post office

In the United States a railway post office, commonly abbreviated as RPO, was a railroad car that was normally operated in passenger service as a means to sort mail en route, in order to speed delivery. The RPO was staffed by highly trained Railway Mail Service postal clerks, and was off-limits to the passengers on the train.

Many American railroads (the Atchison, Topeka and Santa Fe Railway being just one) earned substantial revenues through contracts with the Post Office to carry mail aboard high-speed passenger trains. In fact, a number of companies maintained passenger routes where the financial losses from moving people were more than offset by transporting the mail.