Simulation of airflow and pollution levels caused by severe traffic jam in a road tunnel

Computer simulations were carried out to study airflow patterns and pollution levels due to emissions from vehicles for the westbound Melbourne City Link tunnel under severely congested traffic jam conditions. The time averaged equations for velocity, pressure, temperature and mass fraction of emissions were solved using CFD software FLUENT 6.0. The maximum mass fractions of O2, CO2 and CO were found to be 0.16, 0.14 and 0.002, respectively. These high levels of pollutants were detected despite the fact that roof-mounted fans pushed exhaust fumes out the exit and sucked fresh air in from the inlet of the tunnel. During another condition of power failure, when the fans were not in operation, the flow inside the tunnel was mainly driven by buoyancy and the concentration levels of O2, CO2 and CO were then found to be 0.05, 0.18 and 0.0028, respectively. Theses emissions from the vehicles for both cases posed a threat to human health. To avoid this dangerous situation a multi-pronged approach is needed that includes having alternative sources of power for the fans, ensuring faster evacuation of passengers and drivers, as well as switching-off engines during prolonged traffic standstill.