  One abstract method for the study of network transportation is proposed in
this paper. By interpolating the properties of the edges that constitute
network into the two leading parameters of the nodes, this method can abstract
the configuration of real-life transportation networks without losing the
influence of the distance and the capability of the physical facilities, which
are essential parts of the transportation networks. With this method we can
study network transportation from the local point of view and describe network
congestion in detail, especially the dispersing of congestion. After applying
this method, as an example, to the traffic problem in the process of city
expansion, simulation results show that: the intuitions that with the same rate
of particle generation and the same capacity and power, the smaller the network
is the harder for the network to become congested; and the network will never
be congested if the power of each node equals or is bigger than its capacity
are incorrect. And the distance from one crossroad to another and the width of
the roads can be designed properly, when designing a city, so as to enlarge the
tolerance size of the city in the process of city expansion. This method may
provide more appropriate guide for real-life traffic design of network
transportation.
