As the number and density of access points increases, safety is compromised and speed limits need to be lowered, reducing the traffic carrying capacity of the street or highway. Streets and highways are classified by function. This ranges from the sole purpose of carrying traffic to that of primarily providing access to property. If intersections do not have signals, through traffic flow is given preference to the principal arterial. Access is not provided to abutting property and access is only provided to other streets or highways at grade-separated interchanges.
Freeways are a design type of principal arterials.
A partially access controlled highway designed for high speed travel for the sole purpose of facilitating traffic flow with minimal obstruction from adequately spaced cross traffic. Expressways are a design type of principal arterials. A street or highway designed to both carry traffic and provide access to abutting property. Cross traffic is accommodated at at-grade intersections without signals for streets with low traffic levels. The primary purpose of the minor arterial is to serve moderate length neighborhood trips and to channel traffic from collectors and local streets to principal arterials or expressways.