Transport-related air pollution is a problem of many large urban areas around the world. Its study and control constitute complicated issue, because many largely uncontrollable factors intervene between the available control policies and the harmful effects perceived by society. Traditionally, the amount of air pollutant emissions from motor vehicles (carbon monoxide, hydrocarbons, and oxides of nitrogen) is estimated from emission factors based on trip and vehicle kilometers travelled and appropriate measures of vehicle activity (including average vehicle speed). The kilometres travelled and average speeds are obtained from the output of the typical four-step travel demand model (trip generation, distribution, modal split, and traffic assignment). The emission factors used are based on data collected from road vehicles operators or from test procedures. A modeling framework has been developed to produce detailed emission inventories or large urban areas. Relationships were developed between the time spent in each vehicle operating mode (cruise, acceleration, deceleration, and queuing) and basic link characteristics based on simulations of selected real-world surface street networks and freeway sections using the VISSIM microscopic simulation model, supplemented by field data. These relationships were then incorporated into an Urban Transportation planning system type of four-step travel demand models. The integrated model was applied to a part of Alexandria road network to generate vehicle activity estimates and atmospheric concentrations of polluting gases (CO, VOC, NOX).
