On a traffic control problem

A traffic network can be modeled by a digraph, while the traffic sensor location problem can be studied by using a minimum edge control set which is defined as follows. Let G=(V, E) be a digraph. A subset F of the edge set E is called an edge control set of G if every flow of G is completely determined by F. An edge control set F is said to be minimum if |F| is the least cardinality among all edge control sets of G. In this paper an algorithm for constructing a minimum edge control set of any digraph is established.