https://facts.usps.com/table-facts/Lists mail volume, routes, offices, employees, etc for the years 2015 through 2023.
No that "single piece" first class mail is defined as 1st class mail with postage stamps.
Also first class mail is limited to small envelopes 3.5 oz or less and large envelopes 13oz and under. All else is Package mail.
Package mail includes all so called 1st class packages (stopped as a classification in January 2025) all priority and other package services. Unclear where express and priority-express mail is included. From 2015, there has been a 57% increase in package mail.
Since 2015 there has been a increase from 155 million to 166.6 million delivery points. During the same period routes increased by 7567 to a total of 234,344. As five routes require a minimum of six additional carriers, over 9000 new carriers were needed to handle the 7567 new routes.
The most impressive change, directly due to technology in my opinion, is the fall from 919.5 million to 665.3 (28% decline) retail customer visits. Printing and paying for postage and mailing labels in the home or business has taken off.