A postal carrier route is a group of addresses that receive the same USPS code to aid in efficient mail delivery. Postal carrier route codes are 9 digits: 5 numbers for the ZIP Code, one letter for the carrier route type, and 3 numbers for the carrier route code&emdsh;for example, "92019C005" or "84604R009." A carrier route is generally associated with where a particular mail carrier delivers.
There are approximately 600,000 unique carrier routes in the United States. Approximately half of these are assigned to post-office boxes, leaving approximately 300,000 that represent "boundaries," or delivery areas. These numbers change from month to month. There are about 40,000 valid ZIP Codes in the US, meaning there's an average of 15 carrier routes per ZIP Code.
A saturation mailing is any mailing campaign that mails to at least 90% of the residential addresses within a postal carrier route. Many mailers wrongly think that a saturation mailing must be conducted by ZIP code but the actual definitions from the USPS for the maximum saturation discount uses the carrier route as the defining region.
All major direct mail campaigns run their address files through an address standardization process known as CASS™. Even non-saturation mailings should be CASS-Certified™ prior to mailing to ensure the maximum delivery. CASS™ checks the addresses against a USPS file of deliverable addresses, and corrects any typos in your address file, appends the ZIP+4 and carrier route codes (along with some other codes not relevant to this documentation). You should always run the list against our CASS™ process before doing your mailing. With SmartyStreets, you can use our web-based CASS™ software to quickly, efficiently, and cost-effectively prepare your mailing list with carrier routes.
You can quickly and easily group addresses together with the carrier route information. This allows you to better target specific areas or parts of a ZIP Code. Because constant changes are made to carrier route data, it's important that your address lists have the latest, most valid information.