Microscopic Model of Air Pollutant Concentrations: Comparison of Simulated Results with Measured and Macroscopic Estimates

Abstract

Road traffic is a major source of air pollution, and substantial effort is currently being devoted to the development of both technological and transport policy measures to reduce the impacts. It is well established that the emission of certain pollutants is closely related to both traffic speed and fluctuations in traffic speed. However, conventional transport emission models are largely based on average traffic conditions, and thus they cannot properly represent the effects of policy measures, such as automatic speed control or traffic calming, that directly affect the speed dynamics of the traffic stream. Given the prevalence of such policies, there has been considerable effort to develop improved emissions modeling capabilities. A new approach to the microscopic modeling of air pollution from road traffic is described. This approach can represent detailed speed fluctuations in the flow of traffic, and it is applied to a local network in Maidstone, Kent, in the United Kingdom. A stochastic microscopic traffic flow simulation model (VISSIM), an existing speed-based emission database (MODEM), and a Gaussian dispersion model are combined. Simulated results are compared with a macroscopic model of air pollutant concentrations (DMRB method) and roadside pollutant measurements. Results are encouraging and show a good comparison with the DMRB method and, with some exceptions, good comparisons with trends in measured pollutant concentrations. Statistical differences in the methods, however, suggest that either measurement error or other inaccuracies are present.