USPOD
RPO and HPO
General Schemes

Issued by the Post Office, clerks used this 'General Scheme' as their official reference for dispatching mail via Railway Post Office (RPO), Highway Post Office (HPO), Star Routes (SR), or Mail Messengers (MM) to destination post offices. These publications have three parts; ALPHABETICAL LIST OF POST OFFICES, DISPATCHES TO POST OFFICES, and SEPARATIONS LIST. They also contains an index of all post offices within a state including the class of the PO. Additionally they also includes the distribution lists for post offices grouped by counties by listing the Post office name and the supplying mail routes. There is also a guide for post offices and other mobile units making up dispatches to RPOs and HPOs.
These Guides instructed post offices and other mobile units in the making up the dispatches to RPOs and HPOs by indicating how to separate mail into ordered pouches. The receiving RPO and HPO would work the pouches in that order described in these Schemes so that mail for post offices along each part of the run was sorted in time for dispatch.
Note that these Schemes were in effect for several years so and-written or pasted-in corrections were used to keep the distributions correct.