d countries) will impact future transportation infrastructure requirements. While the model does not explicitly deal with such factors, they are embedded in the base-year data and in the underlying growth rate assumptions (from World Bank and UN sources). It is assumed that the bulk of demographic changes are captured in the model through GDP and population growth (which are considerably lower in industrialised countries with low population growth and population ageing), and through the "convergence" adjustment relating transport infrastructure stock (as a percentage of GDP) towards industrialised levels. Population ageing has been observed in many industrialised countries since the 1980s, SO the trends observed (and incorporated in this model) - a) slowing growth in vehicle ownership rates; b) little/no growth in annual vkm per vehicle; and c) declining rate of road capital stock (as a percentage of GDP) - are felt to adequately capture the future impact of demographic change on road/rail transport use and infrastructure requirements. INFRASTRUCTURE TO 2030: TELECOM, LAND TRANSPORT, WATER AND ELECTRICITY - ISBN 92-64-02398-4 © OECD 2006 KEY FACTORS DRIVING THE FUTURE DEMAND FOR SURFACE TRANSPORT INFRASTRUCTURE Public capital constraint - limit for surface transport A major factor impacting whether transport infrastructure requirements are met is the public willingness to pay for increased land transport mobility - either through general taxation (as mediated by public finance authorities), specific taxation (where this exists) or user-charges (including in support of private participation, i.e. PPP). Road users (direct and "indirect") are a lot like taxpayers in general - SO the finance issue should be, what is most publicly palatable to fund required transport infrastructure? Unfortunately (for land transport authorities), the concept that there should be a "price" for public capital access and that such revenue should remain within the land transport sector appears to be rejected (or overridden) by other publi