Challenge Functional Classification
WHEN TRADITIONAL NETWORKS OF BLOCKS were replaced by dendritic sprawl as the dominant technique for organizing streets in the latter half of the twentieth century (see Rule 36), a new concept was born: functional classification. Functional classification derives from the dendritic (branching) street design system, in which the hierarchy up from local through collector to arterial to highway is organized to correspond with the spectrum of trips from closest and slowest to farthest and fastest. Traffic volume also plays a role, with arterials generally expected to hold more traffic than collectors, which are expected to hold more traffic than locals. It makes sense to organize streets this way when the street pattern is dendritic, since it is easy to know which types of trips will make use of which class of street.