 requirements between net additions to the value of the rail-track capital stock and replacements of depreciating rail-track capital stock. These rail infrastructure investment levels require a relatively constant (to present) rate of spending (as a % of GDP) - and the ratio of the rail-track capital stock-to-GDP is relatively stable over time. There is considerable scope for deliberate government policy to influence modal use - and shift more road use to rail - through the diversion of up to 10% of road new construction (i.e. USD 20-30 billion/year) to rail (in addition to the levels of investment already forecast). These would have some attendant (but possible bearable) consequences in terms of deteriorating overall road infrastructure quality and rising road congestion. Whether vehicle ownership and road traffic use will remain as "constrained" as forecast here - and whether rail traffic will grow as fast as "hoped" - remain to be seen. Despite what public finance authorities may hope for, there is no "sustainability" fiscal dividend involved, SO that public finance and transport authorities will be spending more on road infrastructure in the future. The shift is in terms of moderating the future increase in road infrastructure spending, not in its elimination. 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 The biggest challenge will be 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). Serious discussion is required by public finance/transport authorities and the public over an appropriate "price" for access to public capital, and how such revenue remains within the land transport sector (and is allocated between road and rail). Somewhat perversely, the countries with the