used letter suffixes on several state highways, including "A", "B". "C", "N" (for north) and "S" (for south). A, B and C suffixes were used for spurs of a nearby route, the N and S were legs of IL 113 on either side of the Kankakee River. Illinois has also used special routes, such as "Business", "Alternate", "City", "Bypass" and "Truck" on state-numbered highways. Only a pair of truck routes as well as a batch of Business Routes remain in Illinois, all other special state highways have been renumbered or the markers removed. Primary routes Inventory routes Illinois uses unique "inventory number" signage on rural roads that are owned or maintained by IDOT but may or may not be part of the US or Illinois highway systems. These number signs are white squares, with a green divided circle. The county name is within the dividing line, the mileage from the county line is in the lower half and the inventory or route number in the upper. Number series vary between IDOT Districts, in some areas the number used on otherwise unnumbered routes are a derivative of the former number (i.e.: "913" used on a section of former IL 13) or a sequential number unrelated to the original or former number (such as the 8900 series numbers used in the Galesburg–Macomb area). On many US and Illinois Routes the posted number is used, with or without a preceding descriptor. These signs are not intended for navigation as route numbers are but rather as guides for IDOT crews and contractors and to identify specific intersections, culverts or other features. See also References External links http://www.n9jig.com/ Illinois Highways Page] State routes