A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

What do U.S. Postal Service bar codes mean?

May 10, 1991

Dear Cecil:

After doing my monthly bills I happened to notice all the envelopes provided by my creditors had two sets of bar codes printed on them. The ones at the top were all the same except for a "business reply" envelope, which was slightly different. The ones at the bottom were all different — maybe ZIP codes. What's the deal? If we are picking up the postage, what do the companies get out of it? If it's to ease mail sorting and keep the price of postage down, I guess it hasn't worked.

Cecil replies:

Where is our faith in progress, Mark? Bar-code sorting costs one-fifth as much as older mechanical sorting ($3 versus $15 per thousand pieces as of 1991), and less than one-eleventh as much as hand sorting ($35 per thousand). Eventually the U.S. Postal Service plans to use bar codes on virtually all mail, resulting in a savings of $5 billion per year. In light of this it may seem strange to you that mail rates are going up, but that's because you don't understand the intricacies of postal economics. Join the crowd.

Business reply mail and "courtesy reply" mail (a company sends you a pre-addressed envelope but you have to put the stamp on it) usually have two kinds of marks on them. There's the bar code on the bottom, which is nothing more than the nine-digit ZIP code in machine-readable form, and the "facing identification mark" (FIM), which is five or six vertical lines at the top. The FIM tells the first sorting machine the mail goes through, the "facer canceler," to shunt the letter aside for special handling.

There are three different FIMs — one for business reply mail pre-bar coded by the mailer (this earns the cheapest postage rate); one for non-pre-bar coded BRM (meaning the post office has to put the codes on after accepting the mail for delivery), and one for courtesy reply mail. Businesses pre-code courtesy reply envelopes, which are usually used for bill payments, so the mail will get to them faster and they can deposit the checks sooner. They may earn only a few cents' extra interest per item, but multiply that by a few million checks per year and we're talking serious money.

Chances are you're seeing bar codes on an increasingly large fraction of the mail you receive. The bar codes are put on by the PO using optical character recognition (OCR) equipment. This reads the typewritten address, looks up the proper nine-digit ZIPcode (if missing) in the PO's vast address database, and prints it in bar code form on the envelope. All subsequent sorting is done by relatively inexpensive bar code readers.

In 1993 the postal service began offering discounts to mass mailers to induce them to pre-bar code all their big mailings. The goal was to have 40 percent of all mail pre-bar coded by the mailer, 40 percent coded by the postal service with OCR machines, and the remaining 20 percent — hand-addressed envelopes and the like — bar-coded by clerks viewing the envelope on video.

Awesome, no? You ain't heard nothin' yet. The USPS is also implementing 11-digit ZIP codes. In theory every addressable location in the nation could have its own private ZIP code, although I gather the day when ZIP codes get as specific as phone numbers is still a ways off.  (One problem: In New York, people illegally subletting rent-controlled apartments don't want individual mailbox ZIPs lest the landlord find out — mail often goes into a common bin in the lobby.)  Don't worry, 11-digit ZIPs, known as Advanced Bar Codes or ABCs, are strictly for the use of mass mailers and the postal service — the only hint you and I will have of their existence is that the strip of bar coding on our mail will have gotten longer. Seems pretty complicated, I know, but if you're the postal service and you're competing with fax machines, cellular phones, and Federal Express, you need every technological edge you can get.

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