This section summarises the definitions of transport related objects and activities quantified in the Transport Statistics database and provides notes on uncertainties, ambiguities and alternative sources of data.
Each country has its own definition of transport related information, and these definitions vary from country to country. Wherever possible, a general definition is given that applies to most or all of the countries in the database, with notes of exceptions and differences for specific countries. In some cases an estimate is given of the uncertainty of data.
Some countries provide more data than others, so inevitably there are gaps in the information. Furthermore, information is not precise, and may well not be comparable between countries. This may be because of differences of definition, or differences of measurement processes, or because data is not available for every year. Even for apparently simple quantities such as surface area or population, different sources can give results that differ by a per cent or so. Population can vary by several per cent between sources, and can be revised from time to time by several per cent.
Definitions can cause difficulties, for example:
No figure in any database is precisely accurate; they are simply the best estimates that can be made. Many are not accurate to 1 or 2%; some are not accurate to 10%. In Britain, for example, the total vehicle km of traffic on motorways jumped about 10% as a result of the re-calibration of the model used to estimate traffic km. As such, the data in the Transport Statistics database should be regarded as the best available estimates that are believed to present a fair picture of the situation.
Where data are missing for a country within the Transport Statistics database, it usually means that the original data are not collected for that country.
Published Date: 13 April 2008