The ZIP Code made it possible to distribute all mail by numbers with machines holding the routing associated for each address.
This was a far cry from the knowledge that was necessary before when mobile unit distribution clerks were expected to know the routing for several thousand post offices in their assignment.
This development gave the railroads, knowing they were going to lose the mail revenue, an excuse to get out of the unprofitable passenger train business, something that they had wanted to do for years.
Within about four years there was only one round trip of RPO service left on practically all the trunk lines, and their value was minimal.
It stated that RPO cars on 162 passenger trains in the nation would be phased out of service by the end of the year, affecting 2,224 postal workers.
On a part of this same line, between Philadelphia and Washington, the first recorded "route agent" had been assigned to accompany the mail, 140 years earlier.