This article describes a knowledge-based application in the domain of road traffic management that we have developed following a knowledge modelling approach and the notion of problem-solving method. The article presents first a domain-independent model for a real-time decision support as a structured collection of problem solving methods. Then, it is described how this general model is used to develop an operational version for the domain of traffic management. For this purpose, a particular knowledge modelling tool, called Knowledge Structure Manager (KSM) was applied. Finally, the article shows an application developed for a traffic network of the city of Madrid and it is compared with a second application developed for a different traffic area of the city of Barcelona.