The principal arterial system serves the major centers of activity of a metropolitan area, the highest traffic volume corridors, and the longest trips. It carries a high proportion of the total travel on a minimum of street mileage.

The principal arterial system carries the major portion of trips entering and leaving the City, as well as the majority of through trips desiring to bypass the Central City. This system often carries intra-urban as well as intercity buses. The principal arterial system includes the following types of streets: (1) interstates, (2) other freeways and expressways, and (3) other principal arterials (with no control of access).

For principal arterials, the concept of service to abutting land is subordinate to the provision of travel. Any direct access to land is purely incidental to the primary functional responsibility to traffic movement.

The minor arterial street system interconnects with and augments the principal arterial system and provides services to trips of moderate length at a somewhat lower level of mobility than principal arterials. This system contains facilities that place more emphasis on access than does the principal arterial system. These facilities may carry local bus routes and provide intra-community continuity but ideally should not penetrate neighborhoods.

Collectors.

The collector system may penetrate residential neighborhoods collecting trips from the local system and channeling them onto the arterials. The collector system also distributes trips from the arterial system back into neighborhoods. A smaller number of through trips may also be carried on the collector system. The collector system provides for both land access and local traffic movements within residential neighborhoods and commercial and industrial areas.

Local streets.

The local system primarily provides access to land. It offers the lowest level of mobility, and through traffic is usually deliberately discouraged.