The "RD" designation is followed by a number, which indicates the specific rural route that serves that particular address. For example, an address might be listed as "123 Main Street, RD 1, Springville, CA 95977". In this case, "RD 1" indicates that the address is located on the first rural route in the Springville area.
It's important to note that RD addresses are often used in conjunction with traditional street addresses. This is because the RD number only identifies the rural route, while the street address provides the exact location of the property along that route.
Some countries use different notations for rural addresses, such as "RR" (Rural Route) in Canada, or "CR" (County Road) in the United Kingdom.