Alternatives to a 9-Digit ZIP Code
OTA also examined whether there are viable alternatives to the 9-digit ZIP or ZIP+4 code.
OTA concluded that there are alternative codes. and, indeed, some are used today by other countries. For example, both Canada and Britain use alphanumeric zip codes, that is, a combination of letters and numbers. Other code schemes have been suggested, for example, using individual telephone numbers as zip codes. Telephone numbers would permit sorting down to the level of each individual street address.
In 1976, USPS considered a wide range of alternative ZIP schemes, including scrapping the 5-digit ZIP, using an alphanumeric code, and adding a check digit (e.g., a tenth digit to the 9-digit code). USPS ruled out any change in the basic 5-digit ZIP, since almost all mail (about 94 percent as of 1976) used a ZIP code. A change in the 5-digit code was judged by USPS to be unfair and excessively burdensome to mailers. This left the alternative of adding 3, 4 or 5 digits to the existing 5-digit codes. USPS elected to add 4 digits. Three was ruled out since this would have required an alpha or alphanumeric add-on. Five was likewise ruled out, since the additional digit, while helping to detect code errors and preventing letters from sorting to the wrong destination, would have increased mailing list information and maintenance cost. (The USPS barcode does contain a correction character.)
At the March 5 OTA workshop, several participants expressed the view that the current 9-digit ZIP was not the best code, but that it was too late to make any major changes. The 5-digit ZIP is almost universally accepted and used (98 percent usage) and the 9-digit ZIP directory is now completed. ZIP+4 codes are being distributed to and beginning to be used by large business mailers.