Traffic emission is one of the major problem facing the urban areas. Therefore, there is a need for monitoring air quality in urban centres. Monitoring air quality can be done by using actual measurements or air pollution models. This book presents the modification of general finite line source model developed by Venkatram and Horst to fit the traffic jam, topographical and weather conditions of Tanzania to predict the dispersion of lateral traffic emission. The model uses as its inputs emission rates from motor vehicles,wind speed and direction. Calculated and measured carbon monoxide and nitrogen oxides concentration at three locations from the roadside were compared.Statistical analysis were used to validate the model in which the percentage difference between measured and predicted concentrations were compared. Also the average index of agreement was used. All these statistical measurements showed that there is a correlation between predicted and measured gaseous pollutants emitted by vehicles.