This paper offers an overview of methods which may realistically be used, depending on the specific needs and accuracy required, to describe the emission behaviour of road transport. These include emission computation methods based on real driving behaviour, methods based on road type classification to facilitate emission inventory development, and mileage- or kilometrage related emission balances. No single computational method suffices to meet all such requirements. Example computations are presented to reveal the major areas of application for each method and to show how small changes in input parameters effect the results of the calculations. It is also shown that considerable errors of interpretation can arise when simple methods are applied in the more complex problem areas.