Short bi-directional tunnels present a number of tunnel ventilation problems for both air quality control, in normal operations and smoke control in the event of a fire. The fact that they are seldom fitted with extraction fans causes uncertainty in pollution and smoke control outcomes. In the interests of simplicity and perceived technical risk, active control has been uncommon in tunnels. This paper presents an active control strategy based on the use of feedback control of jet fans to address these issues. Simulations of the control system’s response, based on current work on the Terrace Tunnel (Wellington, New Zealand) are presented to demonstrate the features and performance of the system. Because most newer tunnels are unidirectional for safety reasons, the work is relevant particularly to refurbishment of tunnels.