es, urban sprawl has a major impact on trends in personal/commuter passenger traffic; an increasing proportion is based on multi-purpose travel chains. Another major segment of passenger transport is "leisure/tourism" which takes place over medium to long distances and which is heavily influenced by GDPPC lifestyle factors such as increased leisure time; more frequent but often shorter trips; and diversification of leisure (e.g. visiting friends and relatives, cultural, educational). Passenger traffic (e.g. traveler mobility) is influenced strongly by: 42 Car ownership - where rates have increased much more quickly than income levels and population age structure suggested (e.g. multiple car ownership). Population ageing - where this is slowing the increase in short-haul (local) transport. Family structures - where increasing single-parent families are reducing vehicle occupancy levels and group travel sizes. Factors operating to mediate between GDP growth and passenger transport growth are: Rising vehicle ownership rates, especially with national GDPPC rising through the USD 5 000 "inflection point" (where vehicle ownership accelerates). Urban spatial distribution (density US. sprawl), which support (or limit) the efficiency/viability of rapid public transit as an alternative to private vehicle use. INFRASTRUCTURE TO 2030: TELECOM, LAND TRANSPORT, WATER AND ELECTRICITY - ISBN 92-64-02398-4 - © OECD 2006 4. KEY FACTORS DRIVING THE FUTURE DEMAND FOR SURFACE TRANSPORT INFRASTRUCTURE Social factors (e.g. ageing population, family structure, migration patterns), which support (or limit) the private vehicle trip use (relative to time-choice, and local US. non-local accessibility to family/activities/etc.). The first factor is dominant in some Big 5/developing countries and will result in higher passenger-transport intensity (i.e. faster than national GDP growth), and be supported by the third factor (e.g. younger population, greater international/regional migration). For many industrialised countries (where vehicle own