A Reassessment of the Characterisation of Congestion on an Urban Road Network — Some Theoretical Suggestions and Illustrative Experiments

1.6 Conclusions In this paper we have developed an alternative approach for analysing the phenomenon of congestion within an urban road network. The framework differs from the traditional approach in that it separates out the speed and the density components in the flow variable and uses these to define the ‘price’ and ‘quantitity’ levels of travel demand and supply on a particular link. Having separated out the price and quantity components in demand and supply, we set out a theoretical model to represent the individual demand behaviour for travel activity across a link, based on the concept of a household production function, using a (congested) public infrastructure good (road capacity). The theoretical approach differs from previous contributions where congestion is usually analysed as an externality rather than in terms of household production using a congested public good. Even though the concept of externality and public goods are closely related, the analysis based on the former concept allows us to see more clearly the role of public infrastructure pricing and investment decisions than mere externality analysis. The proposed approach lays down the basic foundations for extending the analysis into a more complex road network structure, drawing on economic equilibrium analysis (analogous to the concept of general equilibrium in conventional economic analysis). We have illustrated the applicability and feasibility of the approach for a simple network of two parallel links.