In 1955, the Nebraska Legislature mandated a new system under which the Department of Roads operated. This legislation included a section stating that any incorporated town of 100 people or more would be served by the Nebraska highway system. In 1969, the requirement was expanded to require a connection to the nearest state highway. These routes, when first implemented in the 1960's, were given regular all-number designations. The designations were based on the mainline road that it "spurred" off. For example, NE-620 was a spur off US-20. If the mainline road was already a 3-digit number, then the spur was given a 4-digit number. For example, NE-2183 was a spur off US-183. By the mid 1970's, a new numbering system was implemented. The secondary highway system routes are referred to as "Spur" and "Link" routes. The spur routes start at a state highway, and usually end a few miles later at a town. The link routes are short connectors between two numbered routes. These routes are numbered in the format "S##X" or "L##X". In each case, the "##" refers to the designation of the county, and the "X" is a letter (A-Z) for that route.