Transport is a considerable source of pollution in cities. The social impacts of transport activities result from emissions of pollutants, greenhouse gases, and noise, as well as traffic accidents. Not every urban investment that reduces such ‘external’ effects of transport will be found acceptable by the public. In order to assess and communicate the social impacts of investments, it is necessary to calculate external costs appropriately. This article discusses issues with estimating the social costs and benefits of transport-related investments in cities. The article also provides a classification of social benefits from urban transport investments and proposes a general methodology for estimating such benefits. Due to the versatility of urban investments, there can be no single, universal method. The article proposes methods for analysing social costs and benefits on the basis of two sample urban investments.