The influence of the piston effect in subway tunnels depends on a train speed, the geometry of a tunnel and a train, the types of air
flow caused by mechanical ventilation and other variable characteristics. Tables and graphs of changes in air flows generated by
the effect of the piston are presented depending on the speed of a train and the degree of fill rate of a tunnel. It is noted that the
piston effect is characterized by two phases. At the first stage, the piston effect and the processes of changing physical fields are
non-stationary whereas at the second stage, the processes become stable. The speed of the circulation flow created by the piston
effect, in accordance with the fill factor of a tunnel, is characterised by a linear relationship; the degree of its growth is directly
proportional to the speed of a train. Based on the results from the present paper it is possible to calculate the velocity and
consumption of an air flow in an underground space. The maximum value of air flow carried out by the piston effect does not exceed
90-100 m3/s. It corresponds to the stationary phase of motion, when the tunnel filling factor α = 0.35 and train speed is in the range
of 40-45 km/h. Based on the obtained numerical simulation results, technological parameters for metro ventilation systems can be
calculated more accurately.