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To a large extent, travelling and mobility are means to an end; they are necessary to enable people to fulfil essential functions, i.e. living, working, gaining education, acquiring necessary supplies, and relaxing, in the most suitable places. The situation is similar for the production of goods and services: division of labour means that production and manufacturing can take place at different sites, which improves the efficiency of production. This causes travel demand, which is measured in different ways depending on the reasons for travel: Frequency of trip making. This metric is a basic indicator of the degree of mobility and concurrent degrees of economic development and lifestyles. In urban settings this figure ranges from 2.2 trips per day and person in developing countries (Padam and Singh 2001) to up to 4.0 trips in industrialized countries (Hu and Reuscher 2004; Sammer 2008). It is expected that in future the frequency of trip making will rise slightly, particularly in developing countries. Generally the frequency of trips is higher in cities than in rural areas because of higher degrees of specialization and division of labour and the higher number of attractive destinations with good accessibility, which are characteristic for urban areas. Distance travelled per day. On the one hand this metric reflects the modes of transport used and on the other hand the spatial structure and settlement density. The lower the settlement density and the more car-oriented an area, the longer the distances travelled per day. Globally these distances vary considerably, from 10 to 60 km per person per day in developing and industrialized countries. In rural areas of developed countries the average distance travelled per day is higher than in cities. In developing countries the opposite is true: in rural areas distances travelled are generally very low (significantly below 10 km per person) and are significantly higher in urban areas due to both higher urban incomes as well as better availability of urban infrastructures and transport options. There is a close positive correlation between the distance travelled per day and transport energy use. Travel time budget per day. This metric is an indication of the time spent travelling. For long periods this figure has been comparatively stable, with a slight tendency to increase; it is currently nearly up to 70 minutes per person/day and 90 minutes per mobile person/day in countries with high motorization and car orientation (Hu and Reuscher 2004; Joly 2004). Assuming that in the long run working hours will decrease due to continued productivity gains, one can expect this figure to increase somewhat in future. Traffic surveys help to determine the travel behaviour which is typical of various sections of the population and for different settings. Caution is however advised when comparing different mobility surveys due to differences in survey coverage and methods (e.g. does the survey include non-motorized modes?) and differences in sampled populations (commuters to work versus total population) and other methodological intricacies. Therefore, there remain serious data gaps for comparable and up-to-date mobility surveys across a wide range of settlements and with comprehensive geographical coverage. The section below summarizes the current state of knowledge with special emphasis on survey comparability rather than recentness of survey date. Despite important data limitations, nonetheless some robust generic patterns can be discerned.