Assessment of the marginal social cost due to congestion using the speed flow function

An integrated strategy was recently set out in Europe regarding the internalization of external costs from transport, i.e. the costs from the negative externalities to the society generated by the transport users. These externalities refer to impacts on the rest of transport users, such as delays due to congestion, accidents and scarcity of infrastructure, and the society, such as pollution, noise, energy dependency and spatial impacts, as well as to the global impact of greenhouse gas emissions on climate change. The external costs derive from expenditures for traffic control, health services, the loss of quality of life, global warming etc., and, added to the users' private costs, formulate the social cost from transport. The marginal social cost is used as a basis for the efficient pricing of transport services and infrastructure in the context of the internalization of external costs.The scope of the present paper is the description of a methodological approach for the assessment of the marginal social cost due to congestion along the urban road network. The first part involves an overview of available methodologies for the assessment of costs due to congestion followed by the description of the proposed approach, which takes advantage of the speed-flow functions of representative segments of the categorised urban road network. The main feature of the approach is that it allows for the estimation of the marginal social cost due to congestion using floating car data (FCD) as input. A pilot application in the city of Thessaloniki, Greece and a comparative analysis of the results in relation to the results of recent studies in Europe are presented in the next part. The paper is concluded with the discussion of the prospects and obstacles for the future implementation and enhancement of the methodological approach.