Interstate (classification for planning and federal map) – The Interstate system consists of all presently designated routes of the interstate system. This is the highest level of arterial roadway and includes the highest levels of access control.
Expressway (classification for planning map only) – Expressways permit through traffic flow through urban areas and between major regional activity centers. Expressways are similar to an interstate with grade separated intersections, but can include some at-grade intersections at cross streets and may or may not be divided. Expressways are intended to provide higher levels of mobility rather than local property access. Expressways may have partial control of access with small amounts of direct land access.
Principal Arterials (classification for planning and federal map) – Principal arterials serve the major regional centers of activity of a metropolitan area, the higher traffic volume corridors, and the longer trips while carrying a higher proportion of the total urban areas travel on a minimum of roadway mileage. Principal arterials carry the major portion of trips entering and leaving the urban area, as well as the majority of through movements. To preserve the long term functionality of such roadways, they should have limited access with less access control than an expressway, but more than a minor arterial.
Minor Arterials (classification for planning and federal map) – Minor arterials interconnect with and augment the principal arterial system and provide service to trips of shorter length at a lower level of travel mobility than principal arterials. Minor arterials also distribute travel to geographic areas smaller than those identified with the higher systems. This classification includes all arterials not included in a higher classification and places more emphasis on land access than principal arterials. Such roadways should still have limited access with less access control than a principal arterial, but more than a collector.
Collectors (classification for federal map only) are roads providing traffic circulation within residential, commercial and industrial areas. Collectors carry trips to and from arterials. Single-family homes are normally discouraged from having driveways onto collectors. Urban collector standards are generally two to three traffic lanes with sidewalks.
