A trip is a one-way journey between an origin and a destination. Origins and destinations are “trip ends”. In trip-based models, locations of trip ends are aggregated into traffic analysis zones (TAZs). A traffic analysis zone is usually represented on networks by a type of node called a “centroid”. A trip is distinguished from a “tour”, which is comprised of two or more trips, with the tour starting and ending at the same location. A trip interchange is an origin-destination pair. One of the properties of an origin-destination pair is the number of trips between them over a given period of time.