D TRANSPORT, WATER AND ELECTRICITY - ISBN 92-64-02398-4 © OECD 2006 4. KEY FACTORS DRIVING THE FUTURE DEMAND FOR SURFACE TRANSPORT INFRASTRUCTURE 0.64 (Big 5 countries); and 0.76 (developing countries). 23 Not surprisingly, the adjustment factors had little impact for high-income countries, but significantly higher PRCS impact for Big 5 and developing countries. There is no logical inconsistency between the ex ante and ex post elasticities. The ex ante Fay-Yepes elasticities represent what was actually experienced over the past three decades, during which there is every reason to believe that there was substantial underinvestment in road capital stock among developing countries. This is the thesis (supported by empirical evidence) from Canning-Pedroni. The convergence adjustment for developing countries is here normative, and represents what needs to occur in order to provide one of the necessary preconditions for rapid economic growth for the Big 5 countries, and for some of the faster-growing developing countries. Risk factors for road new construction The results above are based on economic drivers and assumptions, and do not reflect "wish lists" based on engineering needs. However, as already noted, there are many factors that might prevent (if desirable) or render unnecessary (i.e. make undesirable) the forecast levels of new construction on roads. These include: Conscious government policy to constrain/reduce public expenditures - particularly focused on road new construction (but separate from "sustainability" concerns which are addressed next): Up to (perhaps) 20% of the road new construction (i.e. USD 40-60 billion/ year) could be diverted with some attendant (but possible bearable) consequences in terms of deteriorating overall road infrastructure quality (i.e. as experienced during the 1980-90s) and higher road congestion (especially in urban areas). 24 Conscious government policy to shift transport infrastructure spending and use away from road-vehicles toward rail (including high-speed rail): Up to (