Cost Benefit Analysis to assess urban mobility plans. Consumers’ surplus calculation and integration with transport models

Transport mobility plans, especially at the urban scale, are commonly produced by administrations. However, the decisions involved are often taken on a qualitative basis or, at best, by setting some indicators and verifying how much a plan or a scenario reaches the politically decided targets (e.g. “increasing by 10% the use of bike”). However, given that decisions on plans involve relevant public investments and may also determine radical changes in users’ costs, a more quantitative and comprehensive approach to the evaluation is needed. Cost Benefit Analysis is the tool commonly used to assess public expenditure, but its application to mobility plans introduces further practical and theoretical complexity. The aim of the paper is to discuss how CBA can be used to assess complex and multi-modal mobility plans (involving for example both infrastructural investments and lighter sustainable mobility policies). Firstly we will discuss which are the complexities involved by plan assessments vs. infrastructure assessments. Secondly, we will revise the available approaches, namely the Generalised Costs comparison approach, the Rule of Half and the logsum functions for the perfect integration between CBA and transport models. Thirdly, we will comment the main advantages and problems of the last approach, namely, the logsum, clarifying why it is the most suitable for the assessment of plans made of a broad range of policies and actions. Finally, we will outline an ongoing application for the assessment of the SUMP (Sustainable Urban Mobility Plan) of Milan’s municipality.