Active mobility projects can potentially initiate paradigm shifts in population and urban planning decision-makers. This paper aims to conduct a social cost-benefit analysis of an active mobility project in a Colombian city. The increase of physical activity, reduction of CO2 emissions, and traffic crashes were measured in an area with suitable slopes to promote bicycles for commuting. A social cost-benefit ratio of 1.14 was found, with physical activity and road safety as the most important outcomes of the active mobility infrastructure. Furthermore, a big room for the increase and promotion of cycling as a mode of transport is addressed.