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:
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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