Urban transport networks are sometimes open systems. They have distinct entry points (sources) and exit points (sinks). This nature conflicts with the core requirements of many network models, which assume a closed, strongly connected system where flow is conserved at every node. This chapter presents a rigorous method to resolve this conflict. We introduce the concept of an external balancing node. This abstract node represents the environment outside the defined system boundary. We show how to augment an open network with this node to create a larger, equivalent network. This new network is strongly connected and premagic (flow-balanced). It is therefore suitable for analysis with frameworks like the Ideal Flow Network (IFN) model. We establish the theoretical foundation for this transformation, provide formal proofs, and give numerical examples. We also demonstrate its use in practical urban traffic scenarios