### ! Transport Systems, Networks, Regional Systems, Node and Link Maps

The elemental transport system is the movement of people and/or goods between two points in space and time. The movement is a Line Haul . The end points are Terminals. The line haul is the simplest conceptual model of a transport system. Note that when transportation happens there is relocation in time as well as in space.

LINE and TERMINAL terminology persists even when the system consists of many inter- connected lines, junctions and terminals. Such a system is best described as a network of nodes and links. The nodes and links form a network map.

Mathematically the network can be described as a directed graph.

A transport system is the operation of vehicles and terminals, on a network.

If the nodes are numbered in a convenient way the links or connections of the network can be described in a matrix of 'origins' and 'destinations ', i.e. and OD matrix. There are other descriptions used such as designated routes which interconnect a series of nodes or stations. These routes have been called lines. Lines however sometimes refer to networks.

The conventions used on this continent are:

• NODE: a place where one or more links intersect.
• LINK: a line connecting two nodes.
• ZONE: an area where activity takes place.
• CENTROID: a node at the activity centre of a zone. Centroids are connected to a network by one or more links.
• TERMINAL: a node on a network where traffic (goods - people), an vehicles make a change. They are usually located near centroids. For transshipment or other purposes they may be at a junction or convenient node.

The lengths of the links can be made proportional to the impedance to flow, i.e. distance, or time, or cost, or they can portray actual roadway. Links can be one or two way. If there are some one way links then all links are considered one way. If all the links are two-way then the network is symmetrical and only one direction is required.

Control of the operation of a line haul and/or network may be based on departure or arrival location in space or time. The primary reason for the transport activity will be an increase in utility of the cargo transported, but much of how and when it happens will depend on the objectives of the movements.

E.g. a child will start from home to school and follow a certain route by some mode. What happens will be based on a set of choices that should achieve the goal of getting to the school, and on time. As the song from My Fair Lady states 'Get me to the Church on TIME'

Understanding the objectives of the transport movement determines the control variables.  They will reveal how the important decisions should be approached.

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End to date 060207, ams

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