s in infrastructure spending to GDP, and capital stocks to GDP have been close to "optimal", if somewhat sub-optimal). 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 3. While political factors may have resulted in some uneconomic projects proceeding, and some reorientation of priorities, the aggregate transport infrastructure profiles reflect economic principles (i.e. are cost-beneficial). 4. Generally, there has been chronic under-funding of transport (and other) infrastructure in most Big 5/developing countries, reflecting public finance availability (despite IFI and donor country lending/grants).30 These assumptions allow us to invoke the following lemma: that transport infrastructure requirements estimated on the basis of historical relationships between road capital stock and GDP will also be cost-beneficial - SO that the benefits of road infrastructure spending will exceed their costs. Therefore, the model forecasts of road transport infrastructure requirements (in terms of cost) - namely USD 220-290 billion per year over 2000-30 - also represent a conservative estimate of the expected benefits of such transport infrastructure investments. 31 A similar (but different) assumption may be made about rail transport infrastructure requirements (USD 49-58 billion per year), as much of this is driven by government policy to effect a deliberate modal shift (at the margin) from road to rail, to: a) achieve environmental/sustainability objectives and benefits; and b) to manage rising congestion and postpone future road infrastructure needs. Therefore, the benefits from rail transport infrastructure requirements will involve a lesser degree of economic benefit (in terms of productivity/GDP growth), and a greater degree of environmental/social benefit (likely not reflected in productivity/GDP growth, as currently measured). Productivity/utilisation of transport infrastructure A combined