United States Postal Service - Sorting and Delivery Process

Sorting and Delivery Process

Processing of standard sized envelopes and cards is highly automated, including reading of handwritten addresses. Mail from individual customers and public postboxes is collected by mail carriers into plastic tubs. The tubs are taken to a Processing and Distribution Center (P&DC). There are approximately 275 such centers across the United States, which sort mail for a given region (typically a radius of around 200 miles) and connect with the national network for interregional mail.

At the P&DC, mail is emptied into hampers which are then automatically dumped into a Dual Pass Rough Cull System (DPRCS). As mail travels through the DPRCS, large items, such as packages and mail bundles, are removed from the stream. As the remaining mail enters the first machine for processing standard mail, the Advanced Facer-Canceler System (AFCS), pieces that passed through the DPRCS but do not conform to physical dimensions for processing in the AFCS (i.e. large envelopes or overstuffed standard envelopes) are automatically diverted from the stream. Mail removed from the DPRCS and AFCS is manually processed or sent to parcel sorting machines.

In contrast to the previous system, which merely canceled and postmarked the upper right corner of the envelope, thereby missing any stamps which were inappropriately placed, the Advanced Facer-Canceler System locates indicia (stamp or metered postage mark), regardless of the orientation of the mail as it enters the machine, and cancels it by applying a postmark. Detection of indicia enables the AFCS to determine the orientation of each mailpiece and sort it accordingly, rotating pieces as necessary so all mail is sorted right-side up and faced in the same direction in each output bin.

Mail is output by the machine into three categories: mail already affixed with a bar code and addressed (such as business reply envelopes and cards), mail with machine printed (typed) addresses, and mail with handwritten addresses. Additionally, machines with a recent Optical Character Recognition (OCR) upgrade have the capability to read the address information, including handwritten, and sort the mail based on local or outgoing ZIP codes.

Mail with typed addresses goes to a Multiline Optical Character Reader (MLOCR) which reads the ZIP Code and address information and prints the appropriate bar code onto the envelope. Mail (actually the scanned image of the mail) with handwritten addresses (and machine-printed ones that are not easily recognized) goes to the Remote Bar Coding System. It also corrects spelling errors and, where there is an error, omission, or conflict in the written address, identifies the most likely correct address.

When it has decided on a correct address, it prints the appropriate bar code onto the envelopes, similarly to the MLOCR system. RBCS also has facilities in place, called Remote Encoding Centers, that have humans look at images of mail pieces and enter the address data. The address data is associated with the image via an ID Tag, a fluorescent barcode printed by mail processing equipment on the back of mail pieces.

If a customer has filed a change of address card and his or her mail is detected in the mailstream with the old address, the mailpiece is sent to a machine that automatically connects to a Computerized Forwarding System database to determine the new address. If this address is found, the machine will paste a label over the former address with the current address. The mail is returned to the mailstream to forward to the new location.

Mail with addresses that cannot be resolved by the automated system are separated for human intervention. If a local postal worker can read the address, he or she manually sorts it out according to the ZIP code on the article. If the address cannot be read, mail is either returned to the sender (first-class mail with a valid return address) or is sent to the Mail Recovery Center in Atlanta, Georgia (formerly known as Dead Letter Offices, originated by Benjamin Franklin in the 1770s) where it receives more intense scrutiny, including being opened to determine if any of the contents are a clue. If no valid address can be determined, the items are held for 90 days in case of inquiry by the customer; and if they are not claimed then they are either destroyed or auctioned off at the monthly Postal Service Unclaimed Parcel auction to raise money for the service.

Once the mail is bar coded, it is automatically sorted by a Delivery Bar Code System that reads the bar code and determines the destination of the mailpiece to postal stations.

Regional mail is trucked to the appropriate local post office or kept in the building for carrier routes served directly from the P&DC. Out-of-region mail is trucked to the airport and then flown, usually as baggage on commercial airlines, to the airport nearest the destination station. At the destination P&DC, mail is once again read by a DBCS which sorts the items into their local destinations, including grouping them by individual mail carrier.

At the carrier route level, 95% of letters arrive pre-sorted; the remaining mail must be sorted by hand. The Post Office is working to increase the percentage of automatically sorted mail, including a pilot program to sort "flats".