These roadways serve major centers of metropolitan areas, provide a high degree of mobility, and can also provide mobility through rural areas. Unlike their access-controlled counterparts, these roadways can serve abutting land uses directly. Forms of access for other principal arterial roadways include driveways to specific parcels and at-grade intersections with other roadways. For the most part, roadways that fall into the top three functional classification categories (interstate, other freeways and expressways, and other principal arterials) provide similar service in both urban and rural areas. The primary difference is that multiple arterial routes usually serve a particular urban area, radiating out from the urban center to serve the surrounding region. In contrast, an expanse of a rural area of equal size would be served by a single arterial.

Minor arterials provide service for trips of moderate length, serve geographic areas that are smaller than their higher-arterial counterparts, and offer connectivity to the higher-arterial system. In an urban context, they interconnect and augment the higher-arterial system, provide intra-community continuity, and may carry local bus routes. In rural settings, minor arterials should be identified and spaced at intervals that are consistent with population density so that all developed areas are within a reasonable distance of a higher-level Arterial. In addition, minor arterials in rural areas are typically designed to provide relatively high overall travel speeds, with minimum interference to through movement. The spacing of minor-arterial streets typically may vary from 1/8- to 1/2-mile in the central business district and between 2 and 3 miles in the suburban fringes. Normally, the spacing should not exceed 1 mile in fully developed areas.

Collectors serve a critical role in the roadway network by gathering traffic from local roads and funneling it into the arterial network. Within the context of functional classification, collectors are broken down into two categories: major collectors and minor collectors. Until recently, this division was considered only in the rural environment. Currently, all collectors, regardless of whether they are within a rural area or an urban area, may be sub-stratified into major and minor categories. The determination regarding whether a given collector is a major or minor collector is frequently one of the biggest challenges in functionally classifying a roadway network. In the rural environment, collectors generally serve primarily intra-county travel (rather than statewide) and constitute those routes on which, independent of traffic volume, predominant travel distances are shorter than on arterial routes. Consequently, more moderate speeds may be posted. The distinctions between major collectors and minor collectors are often subtle. In general, major-collector routes are longer in length, have lower connecting-driveway densities, have higher speed limits, are spaced at greater intervals, have higher annual average traffic volumes, and may have more travel lanes than their minor-collector counterparts. Careful consideration should be given to these factors when assigning a major or minor collector designation. In rural areas, annual average daily traffic and spacing may be the most significant designation factors. Since major collectors offer more mobility and minor collectors offer more access, it is beneficial to reexamine these two fundamental concepts of functional classification. Overall, the total mileage of major collectors is typically lower than the total mileage of minor collectors, while the total collector mileage is typically one-third of the local roadway network.