[loi.Ic( Rl-ISFARCH W(ORKING PAPER 2036

# **Summary** findings

Ingram and Liu extend their earlier empirical work by exploring alternative specifications for the relationship between vehicle ownership, road length, and the ratio of vehicles to road length, on the one hand, and income, population, population density, and other variables, on the other.

For the constancy or variability of cross-section income elasticities for each of these variables, they find that:

* The income elasticity of vehicle ownership decreases slightly with income at the national level but is constant at the urban level.

* The income elasticity of road length is constant at the national level but increases with income at the urban level.

* The income elasticity of the vehicle to road ratio decreases with income at both the national and urban level and, at high income levels, becomes negative for urban roads and for national paved roads.

Comparisons of income elasticities from cross-section and time series data indicate that they are generally similar for vehicles, road length, and the velhicle to road ratio at the national level.

But at the urban level the time series income elasticitv of road length (0. 1) is mlich smaller thaln the crosssection elasticity (0.7), and the time series income elasticity of the vehicle to road ratio (0.9) is much larger than the cross-section elasticities (0. I for low income cities and -0.5 for high income cities).

This means that the vehicle to road ratio (a proxy for congestion) is increasing over time in cities, almost in step with per capita income - a trend with dire consequences for urban transport.

Although the urban results are somewhat alarming, the national results indicate that the vehicle to road ratio nationally (especially on paved roads) is relatively low and not rising rapidly. It also shows remarkable stability across country income levels.

This contrast between the national and urban results reinforces the view that urban decentralization is likely to remain the major mode of adjustment to urban congestion.

This paper - a joint product of the Research Advisory Staff and the Transport Division, Transport, Water, and Urban - Development Department is part of a research project on motorization and roads. Copies of the paper are available free from the World Bank, 1818 H Street NW, Washington, DC 20433. Please contact Jean Ponchamni, room MC4-383, telephone 202-473-1022, fax 202-522-0304, Internet address jponchamniCaworldbank.org. Policy Research Working Papers are also posted on the Web at http://www.worldbank.org/html/dec/Publications/Workpapers/home.htnl. The authors may be contacted at gingram(4worldbank.org or zliu@aworldbank.org. December 1 998. (34 pages) _The Policy Research Working Paper Series disseminates the findings of work in progress to encounrae the cxc'a bis,' ot ideas about development issues. An objective of the series is to get the findings ouit quickly, even if the preseniations are less than filly polished. The papers carry the namnes of the authors and should be cited accordinigly. The findings. interpretationis and conicliisioiis explessed in this paper are entirely those of the authors. They do not necessarily represenit the vieis' of the World Bank, its Executive l)irectos, or the coutntries they represent._ Produced **by** the Policy Research Disseminationi Center