With steadily decreasing vehicle emissions, questions of fire and smoke control are of increasing interest and are starting to be the determining factor in the design of the ventilation equipment. The principal methods to study fire and smoke control in the past were full size experiments, small scale tests and computer simulations. En general the problem is treated stationary. The present study concentrates on unsteady flow behaviour due to the traffic change caused by a fire in the tunnel. Realistic traffic behaviour and the influence of a certain smoke production rate at the location of the fire are included. Starting from a stationary solution, this unsteady traffic creates a time-variable pressure difference acting on the tunnel air, which leads to a change in the axial velocity. After a certain time, fire and smoke control mechanisms such as artificial ventilation and traffic control may become active. For a short highway tunnel with longitudinal ventilation, the time dependent axial now velocity in the tunnel is investigated for different traffic, fire and ventilation scenarios. The influence of ventilation and traffic control on smoke propagation is shown. Questions on how and when to interact ideally with the ventilation system are treated. A discussion of the applicability and a qualitative comparison of these theoretical investigations with real fire cases are given.