  Conventionally, methods to solve macroscopic node model are discussed in
algorithm or in algebraic point of view. In this paper, the geometric
interpretation is discussed, focusing on an example in Flotterod and Rohde
(2011). Via observing these diagrams, it is easy to see that deriving
holding-free solution (HFS) is not just an ordinary optimisation problem, but
rather a Pareto frontier-finding problem.
