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Road traffic is a dominant source of urban air pollution. Therefore, it is necessary to quantify emission levels as accurately as possible. In this paper, an overview of methods to describe the emission behavior of road transport is presented. The various methods are emission computation methods based on real driving behavior; methods based on road stretch analysis to facilitate emission inventory development; and mileage-related emission balances. Each computational method has its own range of application. Example computations are presented to reveal the major areas of application for each method and to show how small changes in input parameters affect the results of the calculations. It is also shown that considerable errors of interpretation can arise when simple methods are applied to more complex problem areas. It is not easy to say which method is most accurate, but the more precise the description of the driving behavior and fleet composition, the more reliable the emission estimate will be.The main focus of this paper is emission models. While the origin and quality of traffic data is not discussed, it should be remembered that data such as number of vehicles and number of miles traveled are at least as important as the emission calculation model used.

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