both the rural route number and the box number, for example "RR 5, Box 10." With the creation of the 911 emergency system, it became necessary to discontinue the old rural route numbers in favor of house numbers and street names as used on city routes. This change enabled emergency services to more quickly locate a rural residence. Types of carriers The rural carrier work force is divided into the following categories of employees: Regular carriers (Designation Code 71) For administrative and reporting purposes, regular rural carriers who serve on an established rural route on the basis of triweekly, five, five-and-a-half, or six days in a service week, are considered full-time employees. Part-time flexible rural carriers (Designation Code 76) Part-time flexible rural carriers (PTFs) are those substitutes or rural carrier associates appointed following an assignment posting. These employees provide service on regular and auxiliary routes as directed by management. Substitutes, associates, and reliefs The following employees provide service on established regular and auxiliary rural routes in the absence of regular or auxiliary rural carriers. This service may be as leave replacement and/or covering vacant regular routes pending the selection of regular rural carriers, as an auxiliary assistant or as an auxiliary route carrier: Substitute rural carriers (Designation Code 72) appointed via Form 50 to serve full-time on a vacant regular route or in the absence of a regular carrier for more than 90 calendar days. Substitute rural carriers (Designation Code 73) are those employees hired prior to July 21, 1981, with an appointment without time limitation. Rural carrier associates (Designation Code 74) are appointed via Form 50 to serve full-time on a vacant route or in the absence of the regular carrier for more than 90 calendar days. Designation Code 75 are those employees hired between July 21, 1981 and November 12, 1986 without time limitation. Designation Code 78 are those employees hired from a register or reassigned from rural carrier relief or auxiliary carrier positions, on or after April 11, 1987, without time limitation. Designation Code 79 are appointed via Form 50 after being assigned to the auxiliary route for more than 90 calendar days. Auxiliary rural carriers (Designation Code 77) Persons hired prior to 1981 to serve an auxiliary rural route without time limitation. Assistant Rural Carriers (Designation Code 70-5) Assistant Rural Carriers (ARCs) were added to the 2016 contract. They primarily assist with package delivery on weekends