Numerical evaluation of pollutant dispersion at a toll plaza based on system dynamics and Computational Fluid Dynamics models

The health of tollbooth workers is seriously threatened by long-term exposure to polluted air from vehicle exhausts. Using traffic data collected at a toll plaza, vehicle movements were simulated by a system dynamics model with different traffic volumes and toll collection procedures. This allowed the average travel time of vehicles to be calculated. A three-dimension Computational Fluid Dynamics (CFD) model was used with a k–ε turbulence model to simulate pollutant dispersion at the toll plaza for different traffic volumes and toll collection procedures. It was shown that pollutant concentration around tollbooths increases as traffic volume increases. Whether traffic volume is low or high (1500 vehicles/h or 2500 vehicles/h), pollutant concentration decreases if electronic toll collection (ETC) is adopted. In addition, pollutant concentration around tollbooths decreases as the proportion of ETC-equipped vehicles increases. However, if the proportion of ETC-equipped vehicles is very low and the traffic volume is not heavy, then pollutant concentration increases as the number of ETC lanes increases.

Research highlights
► Using traffic data collected at a toll plaza, a simulation model based on the system dynamics was established to investigate the effects of traffic volume, number and configuration of ETC lanes, and proportion of ETC-equipped vehicles on the average travel time for all vehicles passing through a toll plaza.
► Using the average travel time for all vehicles passing through a toll plaza, pollutant emission levels were calculated and several three-dimension CFD simulations of pollutant dispersion at the toll plaza were conducted using the commercial computer program FLUENT. The fields of velocity flow and pollutant concentration were simulated and the effects of traffic volume and toll collection procedures on pollutant dispersion were discussed.
► Pollutant concentration increases as traffic volume increases. When the mixed toll collection with ETC lanes is adopted, pollutant concentration is lower than when only STC is used. In addition, pollutant concentration decreases as the proportion of ETC-equipped vehicles rises. For the same proportion of ETC-equipped vehicles and when traffic volume is heavy, the advantage of ETC lanes is apparent and the pollutant concentration becomes lower than with STC.