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D5 Annex WP 3: DATABASE METHODOLOGY AND DATABASE USER MANUAL – FREIGHT TRANSPORT DEMAND constructed databases; because of the estimates that have to be made the reliability of the data decreases with the increase of the level of detail. It therefore can be concluded that a reliable transport chain database with a high level of detail can only become available if these data are collected by forms like has been attempted in the MYSTIC project and is being tested in some national pilot exercises (France, Netherlands, Sweden) of which no final results have been obtained yet. In any other case the level of detail has to be reduced to come to a suitable reliability level. Restrictions on the Ideal Database The issue to be discussed is what the ideal transport chain information to be collected must consist. In this chapter the problems to collect the data will be ignored but the focus will only be on possibilities and problems of construction and handling (usage) of such a database. An ideal situation of the database to be constructed will be shown. The ideal transport database has the following general restrictions: · Technical restrictions · Understandability · Policy requirements There still are some technical restrictions. If the database becomes large it becomes more complex and time consuming to perform manipulations and extractions. If the record structure becomes very complex it will take even more effort and time to develop the necessary software. Besides this technical side of having a large and complex database we also have the side of interpretation of the results from this database. If one wants to know the movements between an origin and destination it will be very important to know whether one wants to know the movements of the commodities or the vehicles. The difficulty lies in the fact that now also the movements between transhipment points should be taken into account, making it more complex to make the right restrictions on the database. When having made an extraction from the database for a certain origin and destination, what can be seen? Are these the end points of the vehicle/vessel trip? Does it mean that the commodities transported have actually been switched between modes? Are these endpoints also the origin and destination of the commodities or for which part of the total flow does this hold? Much information should be provided to be able to make the right interpretation of the figures obtained from the database. Also aggregated information, which one is used to, like for instance a modal split figure, becomes more complex. How do we define the modalsplit for a country knowing the transport chain structure of the database? To be able to provide a modalsplit one needs to make assumptions. These assumptions have to be provided together with the figures to be able to make the right interpretations. 152 Document2 27 May 2004
D5 Annex WP 3: DATABASE METHODOLOGY AND DATABASE USER MANUAL – FREIGHT TRANSPORT DEMAND In case different methods are applied based on the different available data sources that can vary significantly among the different countries also some diffusion of interpretations can occur. On some elements of the database and for some geographical areas more estimation will be necessary than for others. It is important that these differences can easily be traced back from the results shown from the database to be able to make the right interpretation. These situations where assumptions have to be made to be able to generate the database and information from this database, and where data can not be shown without the necessary information on these assumptions, we could capture under the ‘understandability’ restriction. This restrictions requires that the database and the surrounding system is structured in such a way that information needed for the interpretation of the information extracted can be easily be made available. In the first place the transport chain freight database should be a simplification of reality in order to be able to understand how and where transport takes place. This means that many variables that could be observed have to be left out. Since each analysis of a problem requires another level of detail of the database. The policy requirement restriction which are in this case the TEN policies, determine which data should be included and which not. This is described in section 4.3. In the next paragraphs realistic possibilities for the format of the transport chain database will be described. The ideal Transport Chain To get a better view of which variables should be included in the transport chain database, an example is presented in figure D.1. Document2 27 May 2004 153
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