A postal carrier route is assigned to a group of addresses to assist the USPS with mail delivery. Each carrier_route_code contains tens to hundreds of ZIP4 codes.
Carrier routes are four-character strings. The first character is coded to describe the type of delivery:
R- a rural route where the mail is delivered in a vehicleC- a city delivery where the mail is delivered on foot by a postal employeeB- a PO Box delivery and cannot be mapped because multiple routes can overlap
These classifications hint at the density of occupants within the carrier_route_code.
All records assigned a carrier_route_code are considered deliverable. carrier_route_code can be used with saturation mailing and is recommended over ZIP Code for this purpose by the USPS.