The high concentration of people in train stations during rush hour poses a significant risk to passenger comfort and safety. Recent technological advancements in real-time crowd counting and pedestrian microsimulations have made it feasible to create responsive gateways for managing passenger flow to prevent overcrowding situations. This paper proposes a simulation-based cost–benefit analysis, utilising the real options methodology commonly employed to assess flexible infrastructure, to estimate the costs and benefits associated with implementing responsive gateways at the London Bridge station, UK, while considering uncertainties in passenger flow and the interests of various stakeholders. Results from the demonstrative example indicate that responsive gateways offer a better service than static ones mainly due to the expected reduction in the risks related to safety, travel time and comfort, which compensates for a higher cost of installation and maintenance. Further research is envisioned to enhance the modelling of passenger flow uncertainties and expand the objective function to encompass additional externalities. The simulation-based cost–benefit analysis proposed in this paper can be extended to a broader range of intelligent transportation systems, considering uncertainties and their diverse impacts on society. Thus, this paper presents a tool that contributes to a more transparent and objective investment decision making process, particularly concerning the development of smart cities.