wth on road capital stock, but it is also observed and used for measures of road use and vehicle ownership. The elasticity of vehicle stock with respect to income (e.g. GDP) is 0.75-1.25, with a mean estimate of 1.0; meanwhile the elasticity of annual per vehicle driving distance with respect to income is 0.05 to 1.60, with a mean estimate 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 of 0.2. Taken together, the figures imply an elasticity of distance travelled with respect to income is 0.65-1.25, with a median estimate of 1.2. 18 World GDP growth of 2.7-3.1% per annum is forecast by the World Bank over 2000-15. Here, the later period growth trend is continued for the entire period to 2030. World population growth of 0.8-1.2% per annum is forecast by the United Nations over 2000-30. The resulting World GDPpc growth rate is 1.8-2.1% per annum. A summary of the key economic growth assumptions are found in Annex 4.A3. Key drivers for vehicle ownership and road use Prior to estimating a model for paved road capital stock and new construction, a forecast for vehicle ownership and road use was made (see Annexes 4.A4 and 4.A5 for forecast details). The key variable is road vehicle ownership, which is clearly linked to GDPpc growth on a log-log basis. A key "threshold" of accelerating vehicle ownership occurs around USD 5 000 per capita GDP. This non-linearity is modeled through a simple step function, with a transition occurring between USD 5 000-10 000 GDPpc. Table 4.3 shows rapid growth in road vehicle ownership per 100 population (vhp) for Big 519 countries (principally China) - with a slow upward trend for the world as a whole. Table 4.3. Vehicle ownership forecast Region vehicles per 100 pop. vehicles per 100 pop. vehicles per 100 pop. vehicles per 100 pop. Industrialised Non-OECD Developing Big 5 Others World Rapid motorisation and growth in vehicle ownership in China (and other